Our handling of user namespaces is more complex than it needs to be. This simplifies the handling by identifying and entering (or creating) the correct userns earlier, so that later code doesn't need to deal with it any more. Along the way we make a number of other cleanups to handling of userns and setting our user and group. This is based on my earlier test command dispatch and performance test cleanup series. Changes since v2: * Correction to man page to match behaviour change in 10/10 * Minor changes to spacing and wording of comments Changes since v1: * Fixed overenthusiastic pruning of #includes when moving the self-isolation code which broke compile on some distro versions David Gibson (10): Don't store UID & GID persistently in the context structure Split checking for root from dropping root privilege Consolidate determination of UID/GID to run as Safer handling if we can't open /proc/self/uid_map Move self-isolation code into a separate file Consolidate validation of pasta namespace options Clean up and rename conf_ns_open() Correctly handle --netns-only in pasta_start_ns() Handle userns isolation and dropping root at the same time Allow --userns when pasta spawns a command Makefile | 8 +- conf.c | 236 ++++++++++++++++++++++++++-------------------------- isolation.c | 210 ++++++++++++++++++++++++++++++++++++++++++++++ isolation.h | 15 ++++ passt.1 | 7 +- passt.c | 116 +------------------------- passt.h | 9 -- pasta.c | 91 ++++++++++++-------- pasta.h | 1 + util.c | 83 ------------------ util.h | 2 - 11 files changed, 412 insertions(+), 366 deletions(-) create mode 100644 isolation.c create mode 100644 isolation.h -- 2.37.3
c->uid and c->gid are first set in conf(), and last used in check_root()
itself called from conf(). Therefore these don't need to be fields in the
long lived context structure and can instead be locals in conf().
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
conf.c | 8 +++++---
passt.h | 5 -----
util.c | 12 ++++++------
util.h | 2 +-
4 files changed, 12 insertions(+), 15 deletions(-)
diff --git a/conf.c b/conf.c
index 2edb4ae..0fe5266 100644
--- a/conf.c
+++ b/conf.c
@@ -1086,6 +1086,8 @@ void conf(struct ctx *c, int argc, char **argv)
uint32_t *dns4 = c->ip4.dns;
int name, ret, mask, b, i;
unsigned int ifi = 0;
+ uid_t uid = 0;
+ gid_t gid = 0;
if (c->mode == MODE_PASTA)
c->no_dhcp_dns = c->no_dhcp_dns_search = 1;
@@ -1208,12 +1210,12 @@ void conf(struct ctx *c, int argc, char **argv)
c->trace = c->debug = c->foreground = 1;
break;
case 12:
- if (c->uid || c->gid) {
+ if (uid || gid) {
err("Multiple --runas options given");
usage(argv[0]);
}
- if (conf_runas(optarg, &c->uid, &c->gid)) {
+ if (conf_runas(optarg, &uid, &gid)) {
err("Invalid --runas option: %s", optarg);
usage(argv[0]);
}
@@ -1497,7 +1499,7 @@ void conf(struct ctx *c, int argc, char **argv)
}
} while (name != -1);
- check_root(c);
+ check_root(&uid, &gid);
if (c->mode == MODE_PASTA) {
if (*netns && optind != argc) {
diff --git a/passt.h b/passt.h
index 347e7c1..3035430 100644
--- a/passt.h
+++ b/passt.h
@@ -144,8 +144,6 @@ struct ip6_ctx {
* @sock_path: Path for UNIX domain socket
* @pcap: Path for packet capture file
* @pid_file: Path to PID file, empty string if not configured
- * @uid: UID we should drop to, if started as root
- * @gid: GID we should drop to, if started as root
* @pasta_netns_fd: File descriptor for network namespace in pasta mode
* @pasta_userns_fd: Descriptor for user namespace to join, -1 once joined
* @netns_only: In pasta mode, don't join or create a user namespace
@@ -198,9 +196,6 @@ struct ctx {
char pcap[PATH_MAX];
char pid_file[PATH_MAX];
- uid_t uid;
- uid_t gid;
-
int pasta_netns_fd;
int pasta_userns_fd;
int netns_only;
diff --git a/util.c b/util.c
index 7e10deb..b2ccb3d 100644
--- a/util.c
+++ b/util.c
@@ -485,7 +485,7 @@ void drop_caps(void)
/**
* check_root() - Check if root in init ns, exit if we can't drop to user
*/
-void check_root(struct ctx *c)
+void check_root(uid_t *uid, gid_t *gid)
{
const char root_uid_map[] = " 0 0 4294967295";
struct passwd *pw;
@@ -506,7 +506,7 @@ void check_root(struct ctx *c)
close(fd);
- if (!c->uid) {
+ if (!*uid) {
fprintf(stderr, "Don't run as root. Changing to nobody...\n");
#ifndef GLIBC_NO_STATIC_NSS
pw = getpwnam("nobody");
@@ -515,17 +515,17 @@ void check_root(struct ctx *c)
exit(EXIT_FAILURE);
}
- c->uid = pw->pw_uid;
- c->gid = pw->pw_gid;
+ *uid = pw->pw_uid;
+ *gid = pw->pw_gid;
#else
(void)pw;
/* Common value for 'nobody', not really specified */
- c->uid = c->gid = 65534;
+ *uid = *gid = 65534;
#endif
}
- if (!setgroups(0, NULL) && !setgid(c->gid) && !setuid(c->uid))
+ if (!setgroups(0, NULL) && !setgid(*gid) && !setuid(*uid))
return;
fprintf(stderr, "Can't change user/group, exiting");
diff --git a/util.h b/util.h
index 8297bec..58312fb 100644
--- a/util.h
+++ b/util.h
@@ -234,7 +234,7 @@ char *line_read(char *buf, size_t len, int fd);
void procfs_scan_listen(struct ctx *c, uint8_t proto, int ip_version, int ns,
uint8_t *map, uint8_t *exclude);
void drop_caps(void);
-void check_root(struct ctx *c);
+void check_root(uid_t *uid, gid_t *gid);
int ns_enter(const struct ctx *c);
void write_pidfile(int fd, pid_t pid);
int __daemon(int pidfile_fd, int devnull_fd);
--
2.37.3
check_root() both checks to see if we are root (in the init namespace),
and if we are drops to an unprivileged user. To make future cleanups
simpler, split the checking for root (now in check_root()) from the actual
dropping of privilege (now in drop_root()).
Note that this does slightly alter semantics. Previously we would only
setuid() if we were originally root (in the init namespace). Now we will
always setuid() and setgid(), though it won't actually change anything if
we weren't privileged to begin with. This also means that we will now
always attempt to switch to the user specified with --runas, even if we
aren't (init namespace) root to begin with. Obviously this will fail with
an error if we weren't privileged to start with. --help and the man page
are updated accordingly.
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
conf.c | 5 +++--
passt.1 | 5 +++--
util.c | 29 ++++++++++++++++++++++++++---
util.h | 1 +
4 files changed, 33 insertions(+), 7 deletions(-)
diff --git a/conf.c b/conf.c
index 0fe5266..545f61d 100644
--- a/conf.c
+++ b/conf.c
@@ -747,8 +747,8 @@ static void usage(const char *name)
info( " default: run in background if started from a TTY");
info( " -e, --stderr Log to stderr too");
info( " default: log to system logger only if started from a TTY");
- info( " --runas UID|UID:GID Use given UID, GID if started as root");
- info( " UID and GID can be numeric, or login and group names");
+ info( " --runas UID|UID:GID Run as given UID, GID, which can be");
+ info( " numeric, or login and group names");
info( " default: drop to user \"nobody\"");
info( " -h, --help Display this help message and exit");
@@ -1500,6 +1500,7 @@ void conf(struct ctx *c, int argc, char **argv)
} while (name != -1);
check_root(&uid, &gid);
+ drop_root(uid, gid);
if (c->mode == MODE_PASTA) {
if (*netns && optind != argc) {
diff --git a/passt.1 b/passt.1
index 61f0e4c..88cc879 100644
--- a/passt.1
+++ b/passt.1
@@ -104,9 +104,10 @@ terminal, and to both system logger and standard error otherwise.
.TP
.BR \-\-runas " " \fIUID\fR|\fIUID:GID\fR|\fILOGIN\fR|\fILOGIN:GROUP\fR
-If started as root, change to given UID and corresponding group if UID is given,
+Attempt to change to given UID and corresponding group if UID is given,
or to given UID and given GID if both are given. Alternatively, login name, or
-login name and group name can be passed.
+login name and group name can be passed. This requires privileges (either
+initial effective UID 0 or CAP_SETUID capability) to work.
Default is to change to user \fInobody\fR if started as root.
.TP
diff --git a/util.c b/util.c
index b2ccb3d..eb25c37 100644
--- a/util.c
+++ b/util.c
@@ -492,7 +492,13 @@ void check_root(uid_t *uid, gid_t *gid)
char buf[BUFSIZ];
int fd;
- if (getuid() && geteuid())
+ if (!*uid)
+ *uid = geteuid();
+
+ if (!*gid)
+ *gid = getegid();
+
+ if (*uid)
return;
if ((fd = open("/proc/self/uid_map", O_RDONLY | O_CLOEXEC)) < 0)
@@ -524,11 +530,28 @@ void check_root(uid_t *uid, gid_t *gid)
*uid = *gid = 65534;
#endif
}
+}
+
+/**
+ * drop_root() - Switch to given UID and GID
+ * @uid: User ID to switch to
+ * @gid: Group ID to switch to
+ */
+void drop_root(uid_t uid, gid_t gid)
+{
+ if (setgroups(0, NULL)) {
+ /* If we don't start with CAP_SETGID, this will EPERM */
+ if (errno != EPERM) {
+ err("Can't drop supplementary groups: %s",
+ strerror(errno));
+ exit(EXIT_FAILURE);
+ }
+ }
- if (!setgroups(0, NULL) && !setgid(*gid) && !setuid(*uid))
+ if (!setgid(gid) && !setuid(uid))
return;
- fprintf(stderr, "Can't change user/group, exiting");
+ err("Can't change user/group, exiting");
exit(EXIT_FAILURE);
}
diff --git a/util.h b/util.h
index 58312fb..e2f686b 100644
--- a/util.h
+++ b/util.h
@@ -235,6 +235,7 @@ void procfs_scan_listen(struct ctx *c, uint8_t proto, int ip_version,
int ns,
uint8_t *map, uint8_t *exclude);
void drop_caps(void);
void check_root(uid_t *uid, gid_t *gid);
+void drop_root(uid_t uid, gid_t gid);
int ns_enter(const struct ctx *c);
void write_pidfile(int fd, pid_t pid);
int __daemon(int pidfile_fd, int devnull_fd);
--
2.37.3
Currently the logic to work out what UID and GID we will run as is spread
across conf(). If --runas is specified it's handled in conf_runas(),
otherwise it's handled by check_root(), which depends on initialization of
the uid and gid variables by either conf() itself or conf_runas().
Make this clearer by putting all the UID and GID logic into a single
conf_ugid() function.
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
conf.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++------
util.c | 50 ------------------------------------
util.h | 1 -
3 files changed, 73 insertions(+), 59 deletions(-)
diff --git a/conf.c b/conf.c
index 545f61d..a97e055 100644
--- a/conf.c
+++ b/conf.c
@@ -1021,6 +1021,70 @@ static int conf_runas(const char *opt, unsigned int *uid, unsigned
int *gid)
#endif /* !GLIBC_NO_STATIC_NSS */
}
+/**
+ * conf_ugid() - Determine UID and GID to run as
+ * @runas: --runas option, may be NULL
+ * @uid: User ID, set on success
+ * @gid: Group ID, set on success
+ *
+ * Return: 0 on success, negative error code on failure
+ */
+static int conf_ugid(const char *runas, uid_t *uid, gid_t *gid)
+{
+ const char root_uid_map[] = " 0 0 4294967295";
+ struct passwd *pw;
+ char buf[BUFSIZ];
+ int ret;
+ int fd;
+
+ /* If user has specified --runas, that takes precedence... */
+ if (runas) {
+ ret = conf_runas(runas, uid, gid);
+ if (ret)
+ err("Invalid --runas option: %s", runas);
+ return ret;
+ }
+
+ /* ...otherwise default to current user and group... */
+ *uid = geteuid();
+ *gid = getegid();
+
+ /* ...as long as it's not root... */
+ if (*uid)
+ return 0;
+
+ /* ...or at least not root in the init namespace... */
+ if ((fd = open("/proc/self/uid_map", O_RDONLY | O_CLOEXEC)) < 0)
+ return 0;
+
+ if (read(fd, buf, BUFSIZ) != sizeof(root_uid_map) ||
+ strncmp(buf, root_uid_map, sizeof(root_uid_map) - 1)) {
+ close(fd);
+ return 0;
+ }
+
+ close(fd);
+
+ /* ...otherwise use nobody:nobody */
+ warn("Don't run as root. Changing to nobody...");
+#ifndef GLIBC_NO_STATIC_NSS
+ pw = getpwnam("nobody");
+ if (!pw) {
+ perror("getpwnam");
+ exit(EXIT_FAILURE);
+ }
+
+ *uid = pw->pw_uid;
+ *gid = pw->pw_gid;
+#else
+ (void)pw;
+
+ /* Common value for 'nobody', not really specified */
+ *uid = *gid = 65534;
+#endif
+ return 0;
+}
+
/**
* conf() - Process command-line arguments and set configuration
* @c: Execution context
@@ -1085,9 +1149,10 @@ void conf(struct ctx *c, int argc, char **argv)
struct fqdn *dnss = c->dns_search;
uint32_t *dns4 = c->ip4.dns;
int name, ret, mask, b, i;
+ const char *runas = NULL;
unsigned int ifi = 0;
- uid_t uid = 0;
- gid_t gid = 0;
+ uid_t uid;
+ gid_t gid;
if (c->mode == MODE_PASTA)
c->no_dhcp_dns = c->no_dhcp_dns_search = 1;
@@ -1210,15 +1275,12 @@ void conf(struct ctx *c, int argc, char **argv)
c->trace = c->debug = c->foreground = 1;
break;
case 12:
- if (uid || gid) {
+ if (runas) {
err("Multiple --runas options given");
usage(argv[0]);
}
- if (conf_runas(optarg, &uid, &gid)) {
- err("Invalid --runas option: %s", optarg);
- usage(argv[0]);
- }
+ runas = optarg;
break;
case 'd':
if (c->debug) {
@@ -1499,7 +1561,10 @@ void conf(struct ctx *c, int argc, char **argv)
}
} while (name != -1);
- check_root(&uid, &gid);
+ ret = conf_ugid(runas, &uid, &gid);
+ if (ret)
+ usage(argv[0]);
+
drop_root(uid, gid);
if (c->mode == MODE_PASTA) {
diff --git a/util.c b/util.c
index eb25c37..ce88aee 100644
--- a/util.c
+++ b/util.c
@@ -482,56 +482,6 @@ void drop_caps(void)
}
}
-/**
- * check_root() - Check if root in init ns, exit if we can't drop to user
- */
-void check_root(uid_t *uid, gid_t *gid)
-{
- const char root_uid_map[] = " 0 0 4294967295";
- struct passwd *pw;
- char buf[BUFSIZ];
- int fd;
-
- if (!*uid)
- *uid = geteuid();
-
- if (!*gid)
- *gid = getegid();
-
- if (*uid)
- return;
-
- if ((fd = open("/proc/self/uid_map", O_RDONLY | O_CLOEXEC)) < 0)
- return;
-
- if (read(fd, buf, BUFSIZ) != sizeof(root_uid_map) ||
- strncmp(buf, root_uid_map, sizeof(root_uid_map) - 1)) {
- close(fd);
- return;
- }
-
- close(fd);
-
- if (!*uid) {
- fprintf(stderr, "Don't run as root. Changing to nobody...\n");
-#ifndef GLIBC_NO_STATIC_NSS
- pw = getpwnam("nobody");
- if (!pw) {
- perror("getpwnam");
- exit(EXIT_FAILURE);
- }
-
- *uid = pw->pw_uid;
- *gid = pw->pw_gid;
-#else
- (void)pw;
-
- /* Common value for 'nobody', not really specified */
- *uid = *gid = 65534;
-#endif
- }
-}
-
/**
* drop_root() - Switch to given UID and GID
* @uid: User ID to switch to
diff --git a/util.h b/util.h
index e2f686b..9626cb5 100644
--- a/util.h
+++ b/util.h
@@ -234,7 +234,6 @@ char *line_read(char *buf, size_t len, int fd);
void procfs_scan_listen(struct ctx *c, uint8_t proto, int ip_version, int ns,
uint8_t *map, uint8_t *exclude);
void drop_caps(void);
-void check_root(uid_t *uid, gid_t *gid);
void drop_root(uid_t uid, gid_t gid);
int ns_enter(const struct ctx *c);
void write_pidfile(int fd, pid_t pid);
--
2.37.3
passt is allowed to run as "root" (UID 0) in a user namespace, but notas
real root in the init namespace. We read /proc/self/uid_map to determine
if we're in the init namespace or not.
If we're unable to open /proc/self/uid_map we assume we're ok and
continue running as UID 0. This seems unwise. The only instances I
can think of where uid_map won't be available are if the host kernel
doesn't support namespaces, or /proc is not mounted. In neither case
is it safe to assume we're "not really" root and continue (although in
practice we'd likely fail for other reasons pretty soon anyway).
Therefore, fail with an error in this case, instead of carrying on.
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
conf.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/conf.c b/conf.c
index a97e055..b669f5d 100644
--- a/conf.c
+++ b/conf.c
@@ -1054,8 +1054,12 @@ static int conf_ugid(const char *runas, uid_t *uid, gid_t *gid)
return 0;
/* ...or at least not root in the init namespace... */
- if ((fd = open("/proc/self/uid_map", O_RDONLY | O_CLOEXEC)) < 0)
- return 0;
+ if ((fd = open("/proc/self/uid_map", O_RDONLY | O_CLOEXEC)) < 0) {
+ ret = -errno;
+ err("Can't determine if we're in init namespace: %s",
+ strerror(-ret));
+ return ret;
+ }
if (read(fd, buf, BUFSIZ) != sizeof(root_uid_map) ||
strncmp(buf, root_uid_map, sizeof(root_uid_map) - 1)) {
--
2.37.3
passt/pasta contains a number of routines designed to isolate passt from
the rest of the system for security. These are spread through util.c and
passt.c. Move them together into a new isolation.c file.
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
Makefile | 8 +--
conf.c | 1 +
isolation.c | 167 ++++++++++++++++++++++++++++++++++++++++++++++++++++
isolation.h | 15 +++++
passt.c | 113 +----------------------------------
pasta.c | 1 +
util.c | 51 ----------------
util.h | 2 -
8 files changed, 189 insertions(+), 169 deletions(-)
create mode 100644 isolation.c
create mode 100644 isolation.h
diff --git a/Makefile b/Makefile
index 644a541..af3d1ff 100644
--- a/Makefile
+++ b/Makefile
@@ -32,16 +32,16 @@ CFLAGS += -DRLIMIT_STACK_VAL=$(RLIMIT_STACK_VAL)
CFLAGS += -DARCH=\"$(TARGET_ARCH)\"
PASST_SRCS = arch.c arp.c checksum.c conf.c dhcp.c dhcpv6.c icmp.c igmp.c \
- lineread.c mld.c ndp.c netlink.c packet.c passt.c pasta.c pcap.c \
- siphash.c tap.c tcp.c tcp_splice.c udp.c util.c
+ isolation.c lineread.c mld.c ndp.c netlink.c packet.c passt.c pasta.c \
+ pcap.c siphash.c tap.c tcp.c tcp_splice.c udp.c util.c
QRAP_SRCS = qrap.c
SRCS = $(PASST_SRCS) $(QRAP_SRCS)
MANPAGES = passt.1 pasta.1 qrap.1
PASST_HEADERS = arch.h arp.h checksum.h conf.h dhcp.h dhcpv6.h icmp.h \
- lineread.h ndp.h netlink.h packet.h passt.h pasta.h pcap.h \
- siphash.h tap.h tcp.h tcp_splice.h udp.h util.h
+ isolation.h lineread.h ndp.h netlink.h packet.h passt.h pasta.h \
+ pcap.h siphash.h tap.h tcp.h tcp_splice.h udp.h util.h
HEADERS = $(PASST_HEADERS)
# On gcc 11.2, with -O2 and -flto, tcp_hash() and siphash_20b(), if inlined,
diff --git a/conf.c b/conf.c
index b669f5d..d9e7472 100644
--- a/conf.c
+++ b/conf.c
@@ -40,6 +40,7 @@
#include "tcp.h"
#include "pasta.h"
#include "lineread.h"
+#include "isolation.h"
/**
* get_bound_ports() - Get maps of ports with bound sockets
diff --git a/isolation.c b/isolation.c
new file mode 100644
index 0000000..41ca888
--- /dev/null
+++ b/isolation.c
@@ -0,0 +1,167 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+/* PASST - Plug A Simple Socket Transport
+ * for qemu/UNIX domain socket mode
+ *
+ * PASTA - Pack A Subtle Tap Abstraction
+ * for network namespace/tap device mode
+ *
+ * isolation.c - Self isolation helpers
+ *
+ * Copyright Red Hat
+ * Author: Stefano Brivio <sbrivio(a)redhat.com>
+ * Author: David Gibson <david(a)gibson.dropbear.id.au>
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <grp.h>
+#include <inttypes.h>
+#include <limits.h>
+#include <pwd.h>
+#include <sched.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+#include <sys/mount.h>
+#include <sys/prctl.h>
+#include <sys/socket.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <netinet/in.h>
+#include <netinet/if_ether.h>
+
+#include <linux/audit.h>
+#include <linux/capability.h>
+#include <linux/filter.h>
+#include <linux/seccomp.h>
+
+#include "util.h"
+#include "seccomp.h"
+#include "passt.h"
+#include "isolation.h"
+
+/**
+ * drop_caps() - Drop capabilities we might have except for CAP_NET_BIND_SERVICE
+ */
+void drop_caps(void)
+{
+ int i;
+
+ for (i = 0; i < 64; i++) {
+ if (i == CAP_NET_BIND_SERVICE)
+ continue;
+
+ prctl(PR_CAPBSET_DROP, i, 0, 0, 0);
+ }
+}
+
+/**
+ * drop_root() - Switch to given UID and GID
+ * @uid: User ID to switch to
+ * @gid: Group ID to switch to
+ */
+void drop_root(uid_t uid, gid_t gid)
+{
+ if (setgroups(0, NULL)) {
+ /* If we don't start with CAP_SETGID, this will EPERM */
+ if (errno != EPERM) {
+ err("Can't drop supplementary groups: %s",
+ strerror(errno));
+ exit(EXIT_FAILURE);
+ }
+ }
+
+ if (!setgid(gid) && !setuid(uid))
+ return;
+
+ err("Can't change user/group, exiting");
+ exit(EXIT_FAILURE);
+}
+
+/**
+ * sandbox() - Unshare IPC, mount, PID, UTS, and user namespaces, "unmount"
root
+ *
+ * Return: negative error code on failure, zero on success
+ */
+int sandbox(struct ctx *c)
+{
+ int flags = CLONE_NEWIPC | CLONE_NEWNS | CLONE_NEWUTS;
+
+ if (!c->netns_only) {
+ if (c->pasta_userns_fd == -1)
+ flags |= CLONE_NEWUSER;
+ else
+ setns(c->pasta_userns_fd, CLONE_NEWUSER);
+ }
+
+ c->pasta_userns_fd = -1;
+
+ /* If we run in foreground, we have no chance to actually move to a new
+ * PID namespace. For passt, use CLONE_NEWPID anyway, in case somebody
+ * ever gets around seccomp profiles -- there's no harm in passing it.
+ */
+ if (!c->foreground || c->mode == MODE_PASST)
+ flags |= CLONE_NEWPID;
+
+ if (unshare(flags)) {
+ perror("unshare");
+ return -errno;
+ }
+
+ if (mount("", "/", "", MS_UNBINDABLE | MS_REC, NULL)) {
+ perror("mount /");
+ return -errno;
+ }
+
+ if (mount("", TMPDIR, "tmpfs",
+ MS_NODEV | MS_NOEXEC | MS_NOSUID | MS_RDONLY,
+ "nr_inodes=2,nr_blocks=0")) {
+ perror("mount tmpfs");
+ return -errno;
+ }
+
+ if (chdir(TMPDIR)) {
+ perror("chdir");
+ return -errno;
+ }
+
+ if (syscall(SYS_pivot_root, ".", ".")) {
+ perror("pivot_root");
+ return -errno;
+ }
+
+ if (umount2(".", MNT_DETACH | UMOUNT_NOFOLLOW)) {
+ perror("umount2");
+ return -errno;
+ }
+
+ drop_caps(); /* Relative to the new user namespace this time. */
+
+ return 0;
+}
+
+/**
+ * seccomp() - Set up seccomp filters depending on mode, won't return on failure
+ * @c: Execution context
+ */
+void seccomp(const struct ctx *c)
+{
+ struct sock_fprog prog;
+
+ if (c->mode == MODE_PASST) {
+ prog.len = (unsigned short)ARRAY_SIZE(filter_passt);
+ prog.filter = filter_passt;
+ } else {
+ prog.len = (unsigned short)ARRAY_SIZE(filter_pasta);
+ prog.filter = filter_pasta;
+ }
+
+ if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) ||
+ prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) {
+ perror("prctl");
+ exit(EXIT_FAILURE);
+ }
+}
diff --git a/isolation.h b/isolation.h
new file mode 100644
index 0000000..2540a35
--- /dev/null
+++ b/isolation.h
@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: AGPL-3.0-or-later
+ * Copyright Red Hat
+ * Author: Stefano Brivio <sbrivio(a)redhat.com>
+ * Author: David Gibson <david(a)gibson.dropbear.id.au>
+ */
+
+#ifndef ISOLATION_H
+#define ISOLATION_H
+
+void drop_caps(void);
+void drop_root(uid_t uid, gid_t gid);
+int sandbox(struct ctx *c);
+void seccomp(const struct ctx *c);
+
+#endif /* ISOLATION_H */
diff --git a/passt.c b/passt.c
index bbf53d9..2a8314c 100644
--- a/passt.c
+++ b/passt.c
@@ -19,51 +19,25 @@
* created in a separate network namespace).
*/
-#include <sched.h>
-#include <stdio.h>
#include <sys/epoll.h>
-#include <sys/socket.h>
-#include <sys/types.h>
-#include <sys/stat.h>
-#include <dirent.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/resource.h>
-#include <sys/uio.h>
-#include <sys/syscall.h>
-#include <sys/wait.h>
-#include <sys/mount.h>
-#include <netinet/ip.h>
-#include <net/ethernet.h>
-#include <libgen.h>
#include <stdlib.h>
#include <unistd.h>
-#include <net/if.h>
#include <netdb.h>
#include <string.h>
#include <errno.h>
#include <time.h>
#include <syslog.h>
-#include <sys/stat.h>
#include <sys/prctl.h>
-#include <stddef.h>
-#include <netinet/udp.h>
-#include <netinet/tcp.h>
#include <netinet/if_ether.h>
-#include <linux/seccomp.h>
-#include <linux/audit.h>
-#include <linux/filter.h>
-#include <linux/icmpv6.h>
-
#include "util.h"
-#include "seccomp.h"
#include "passt.h"
#include "dhcp.h"
#include "dhcpv6.h"
-#include "icmp.h"
-#include "tcp.h"
-#include "udp.h"
+#include "isolation.h"
#include "pcap.h"
#include "tap.h"
#include "conf.h"
@@ -166,91 +140,6 @@ void proto_update_l2_buf(const unsigned char *eth_d, const unsigned
char *eth_s,
udp_update_l2_buf(eth_d, eth_s, ip_da);
}
-/**
- * seccomp() - Set up seccomp filters depending on mode, won't return on failure
- * @c: Execution context
- */
-static void seccomp(const struct ctx *c)
-{
- struct sock_fprog prog;
-
- if (c->mode == MODE_PASST) {
- prog.len = (unsigned short)ARRAY_SIZE(filter_passt);
- prog.filter = filter_passt;
- } else {
- prog.len = (unsigned short)ARRAY_SIZE(filter_pasta);
- prog.filter = filter_pasta;
- }
-
- if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0) ||
- prctl(PR_SET_SECCOMP, SECCOMP_MODE_FILTER, &prog)) {
- perror("prctl");
- exit(EXIT_FAILURE);
- }
-}
-
-/**
- * sandbox() - Unshare IPC, mount, PID, UTS, and user namespaces, "unmount"
root
- *
- * Return: negative error code on failure, zero on success
- */
-static int sandbox(struct ctx *c)
-{
- int flags = CLONE_NEWIPC | CLONE_NEWNS | CLONE_NEWUTS;
-
- if (!c->netns_only) {
- if (c->pasta_userns_fd == -1)
- flags |= CLONE_NEWUSER;
- else
- setns(c->pasta_userns_fd, CLONE_NEWUSER);
- }
-
- c->pasta_userns_fd = -1;
-
- /* If we run in foreground, we have no chance to actually move to a new
- * PID namespace. For passt, use CLONE_NEWPID anyway, in case somebody
- * ever gets around seccomp profiles -- there's no harm in passing it.
- */
- if (!c->foreground || c->mode == MODE_PASST)
- flags |= CLONE_NEWPID;
-
- if (unshare(flags)) {
- perror("unshare");
- return -errno;
- }
-
- if (mount("", "/", "", MS_UNBINDABLE | MS_REC, NULL)) {
- perror("mount /");
- return -errno;
- }
-
- if (mount("", TMPDIR, "tmpfs",
- MS_NODEV | MS_NOEXEC | MS_NOSUID | MS_RDONLY,
- "nr_inodes=2,nr_blocks=0")) {
- perror("mount tmpfs");
- return -errno;
- }
-
- if (chdir(TMPDIR)) {
- perror("chdir");
- return -errno;
- }
-
- if (syscall(SYS_pivot_root, ".", ".")) {
- perror("pivot_root");
- return -errno;
- }
-
- if (umount2(".", MNT_DETACH | UMOUNT_NOFOLLOW)) {
- perror("umount2");
- return -errno;
- }
-
- drop_caps(); /* Relative to the new user namespace this time. */
-
- return 0;
-}
-
/**
* exit_handler() - Signal handler for SIGQUIT and SIGTERM
* @unused: Unused, handler deals with SIGQUIT and SIGTERM only
diff --git a/pasta.c b/pasta.c
index a844af2..0bdb655 100644
--- a/pasta.c
+++ b/pasta.c
@@ -40,6 +40,7 @@
#include "util.h"
#include "passt.h"
+#include "isolation.h"
#include "netlink.h"
/* PID of child, in case we created a namespace */
diff --git a/util.c b/util.c
index ce88aee..f709838 100644
--- a/util.c
+++ b/util.c
@@ -13,30 +13,17 @@
*/
#include <sched.h>
-#include <stdio.h>
-#include <stdint.h>
-#include <stddef.h>
#include <stdlib.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <net/ethernet.h>
-#include <net/if.h>
-#include <netinet/tcp.h>
-#include <netinet/udp.h>
#include <sys/epoll.h>
-#include <sys/prctl.h>
-#include <sys/types.h>
-#include <sys/stat.h>
#include <fcntl.h>
#include <syslog.h>
#include <stdarg.h>
#include <string.h>
#include <time.h>
#include <errno.h>
-#include <pwd.h>
-#include <grp.h>
-
-#include <linux/capability.h>
#include "util.h"
#include "passt.h"
@@ -467,44 +454,6 @@ void procfs_scan_listen(struct ctx *c, uint8_t proto, int ip_version,
int ns,
}
}
-/**
- * drop_caps() - Drop capabilities we might have except for CAP_NET_BIND_SERVICE
- */
-void drop_caps(void)
-{
- int i;
-
- for (i = 0; i < 64; i++) {
- if (i == CAP_NET_BIND_SERVICE)
- continue;
-
- prctl(PR_CAPBSET_DROP, i, 0, 0, 0);
- }
-}
-
-/**
- * drop_root() - Switch to given UID and GID
- * @uid: User ID to switch to
- * @gid: Group ID to switch to
- */
-void drop_root(uid_t uid, gid_t gid)
-{
- if (setgroups(0, NULL)) {
- /* If we don't start with CAP_SETGID, this will EPERM */
- if (errno != EPERM) {
- err("Can't drop supplementary groups: %s",
- strerror(errno));
- exit(EXIT_FAILURE);
- }
- }
-
- if (!setgid(gid) && !setuid(uid))
- return;
-
- err("Can't change user/group, exiting");
- exit(EXIT_FAILURE);
-}
-
/**
* ns_enter() - Enter configured user (unless already joined) and network ns
* @c: Execution context
diff --git a/util.h b/util.h
index 9626cb5..1003303 100644
--- a/util.h
+++ b/util.h
@@ -233,8 +233,6 @@ int bitmap_isset(const uint8_t *map, int bit);
char *line_read(char *buf, size_t len, int fd);
void procfs_scan_listen(struct ctx *c, uint8_t proto, int ip_version, int ns,
uint8_t *map, uint8_t *exclude);
-void drop_caps(void);
-void drop_root(uid_t uid, gid_t gid);
int ns_enter(const struct ctx *c);
void write_pidfile(int fd, pid_t pid);
int __daemon(int pidfile_fd, int devnull_fd);
--
2.37.3
There are a number of different ways to specify namespaces for pasta to
use. Some combinations are valid and some are not. Currently validation
for these is spread across several places: conf_ns_pid() validates PID
options specifically. Near its callsite in conf() several other checks
are made. Some additional checks are made in conf_ns_open() and finally
theres a check just before the call to pasta_start_ns().
This is quite hard to follow. Make it easier by putting all the validation
logic together in a new conf_pasta_ns() function, which subsumes
conf_ns_pid(). This reveals that some of the checks were redundant with
each other, so remove those.
For good measure, rename conf_netns() to conf_netns_opt() to make it
clearer its handling just the --netns option specifically, not overall
configuration of the netns.
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
conf.c | 83 +++++++++++++++++++++++++++++-----------------------------
1 file changed, 42 insertions(+), 41 deletions(-)
diff --git a/conf.c b/conf.c
index d9e7472..d1afea9 100644
--- a/conf.c
+++ b/conf.c
@@ -491,13 +491,13 @@ out:
}
/**
- * conf_netns() - Parse --netns option
+ * conf_netns_opt() - Parse --netns option
* @netns: buffer of size PATH_MAX, updated with netns path
* @arg: --netns argument
*
* Return: 0 on success, negative error code otherwise
*/
-static int conf_netns(char *netns, const char *arg)
+static int conf_netns_opt(char *netns, const char *arg)
{
int ret;
@@ -518,40 +518,59 @@ static int conf_netns(char *netns, const char *arg)
}
/**
- * conf_ns_pid() - Parse non-option argument as a PID
+ * conf_pasta_ns() - Validate all pasta namespace options
+ * @netns_only: Don't use userns, may be updated
* @userns: buffer of size PATH_MAX, initially contains --userns
* argument (may be empty), updated with userns path
* @netns: buffer of size PATH_MAX, initial contains --netns
* argument (may be empty), updated with netns path
- * @arg: PID of network namespace
+ * @optind: Index of first non-option argument
+ * @argc: Number of arguments
+ * @argv: Command line arguments
*
* Return: 0 on success, negative error code otherwise
*/
-static int conf_ns_pid(char *userns, char *netns, const char *arg)
+static int conf_pasta_ns(int *netns_only, char *userns, char *netns,
+ int optind, int argc, char *argv[])
{
- char *endptr;
- long pidval;
+ if (*netns_only && *userns) {
+ err("Both --userns and --netns-only given");
+ return -EINVAL;
+ }
- if (*netns) {
- err("Both --netns and PID given");
+ if (*netns && optind != argc) {
+ err("Both --netns and PID or command given");
return -EINVAL;
}
- pidval = strtol(arg, &endptr, 10);
- if (!*endptr) {
- /* Looks like a pid */
- if (pidval < 0 || pidval > INT_MAX) {
- err("Invalid PID %s", arg);
- return -EINVAL;
+ if (optind + 1 == argc) {
+ char *endptr;
+ long pidval;
+
+ pidval = strtol(argv[optind], &endptr, 10);
+ if (!*endptr) {
+ /* Looks like a pid */
+ if (pidval < 0 || pidval > INT_MAX) {
+ err("Invalid PID %s", argv[optind]);
+ return -EINVAL;
+ }
+
+ snprintf(netns, PATH_MAX, "/proc/%ld/ns/net", pidval);
+ if (!*userns)
+ snprintf(userns, PATH_MAX, "/proc/%ld/ns/user",
+ pidval);
}
+ }
- snprintf(netns, PATH_MAX, "/proc/%ld/ns/net", pidval);
- if (!*userns)
- snprintf(userns, PATH_MAX, "/proc/%ld/ns/user", pidval);
- return 0;
+ if (*userns && !*netns) {
+ err("--userns requires --netns or PID");
+ return -EINVAL;
}
- /* Not a PID, later code will treat as a command */
+ /* Attaching to a netns/PID, with no userns given */
+ if (*netns && !*userns)
+ *netns_only = 1;
+
return 0;
}
@@ -585,11 +604,6 @@ static int conf_ns_open(struct ctx *c, const char *userns, const char
*netns)
{
int ufd = -1, nfd = -1;
- if (c->netns_only && *userns) {
- err("Both --userns and --netns-only given");
- return -EINVAL;
- }
-
nfd = open(netns, O_RDONLY | O_CLOEXEC);
if (nfd < 0) {
err("Couldn't open network namespace %s", netns);
@@ -607,7 +621,6 @@ static int conf_ns_open(struct ctx *c, const char *userns, const char
*netns)
c->pasta_netns_fd = nfd;
c->pasta_userns_fd = ufd;
- c->netns_only = !*userns;
NS_CALL(conf_ns_check, c);
@@ -1194,7 +1207,7 @@ void conf(struct ctx *c, int argc, char **argv)
usage(argv[0]);
}
- ret = conf_netns(netns, optarg);
+ ret = conf_netns_opt(netns, optarg);
if (ret < 0)
usage(argv[0]);
break;
@@ -1573,17 +1586,9 @@ void conf(struct ctx *c, int argc, char **argv)
drop_root(uid, gid);
if (c->mode == MODE_PASTA) {
- if (*netns && optind != argc) {
- err("Both --netns and PID or command given");
- usage(argv[0]);
- } else if (optind + 1 == argc) {
- ret = conf_ns_pid(userns, netns, argv[optind]);
- if (ret < 0)
- usage(argv[0]);
- } else if (*userns && !*netns && optind == argc) {
- err("--userns requires --netns or PID");
+ if (conf_pasta_ns(&c->netns_only, userns, netns,
+ optind, argc, argv) < 0)
usage(argv[0]);
- }
} else if (optind != argc) {
usage(argv[0]);
}
@@ -1597,10 +1602,6 @@ void conf(struct ctx *c, int argc, char **argv)
if (ret < 0)
usage(argv[0]);
} else {
- if (*userns) {
- err("Both --userns and command given");
- usage(argv[0]);
- }
pasta_start_ns(c, argc - optind, argv + optind);
}
}
--
2.37.3
conf_ns_open() opens file descriptors for the namespaces pasta needs, but
it doesnt really have anything to do with configuration any more. For
better clarity, move it to pasta.c and rename it pasta_open_ns(). This
makes the symmetry between it and pasta_start_ns() more clear, since these
represent the two basic ways that pasta can operate, either attaching to
an existing namespace/process or spawning a new one.
Since its no longer validating options, the errors it could return
shouldn't cause a usage message. Just exit directly with an error instead.
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
conf.c | 72 +--------------------------------------------------------
pasta.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++
pasta.h | 1 +
3 files changed, 68 insertions(+), 71 deletions(-)
diff --git a/conf.c b/conf.c
index d1afea9..8477a6e 100644
--- a/conf.c
+++ b/conf.c
@@ -20,7 +20,6 @@
#include <sched.h>
#include <sys/types.h>
#include <sys/stat.h>
-#include <libgen.h>
#include <limits.h>
#include <grp.h>
#include <pwd.h>
@@ -574,73 +573,6 @@ static int conf_pasta_ns(int *netns_only, char *userns, char *netns,
return 0;
}
-/**
- * conf_ns_check() - Check if we can enter configured namespaces
- * @arg: Execution context
- *
- * Return: 0
- */
-static int conf_ns_check(void *arg)
-{
- struct ctx *c = (struct ctx *)arg;
-
- if ((!c->netns_only && setns(c->pasta_userns_fd, CLONE_NEWUSER)) ||
- setns(c->pasta_netns_fd, CLONE_NEWNET))
- c->pasta_userns_fd = c->pasta_netns_fd = -1;
-
- return 0;
-
-}
-
-/**
- * conf_ns_open() - Open network, user namespaces descriptors from configuration
- * @c: Execution context
- * @userns: --userns argument, can be an empty string
- * @netns: network namespace path
- *
- * Return: 0 on success, negative error code otherwise
- */
-static int conf_ns_open(struct ctx *c, const char *userns, const char *netns)
-{
- int ufd = -1, nfd = -1;
-
- nfd = open(netns, O_RDONLY | O_CLOEXEC);
- if (nfd < 0) {
- err("Couldn't open network namespace %s", netns);
- return -ENOENT;
- }
-
- if (!c->netns_only && *userns) {
- ufd = open(userns, O_RDONLY | O_CLOEXEC);
- if (ufd < 0) {
- close(nfd);
- err("Couldn't open user namespace %s", userns);
- return -ENOENT;
- }
- }
-
- c->pasta_netns_fd = nfd;
- c->pasta_userns_fd = ufd;
-
- NS_CALL(conf_ns_check, c);
-
- if (c->pasta_netns_fd < 0) {
- err("Couldn't switch to pasta namespaces");
- return -ENOENT;
- }
-
- if (!c->no_netns_quit) {
- char buf[PATH_MAX];
-
- strncpy(buf, netns, PATH_MAX);
- strncpy(c->netns_base, basename(buf), PATH_MAX - 1);
- strncpy(buf, netns, PATH_MAX);
- strncpy(c->netns_dir, dirname(buf), PATH_MAX - 1);
- }
-
- return 0;
-}
-
/**
* conf_ip4() - Verify or detect IPv4 support, get relevant addresses
* @ifi: Host interface to attempt (0 to determine one)
@@ -1598,9 +1530,7 @@ void conf(struct ctx *c, int argc, char **argv)
if (c->mode == MODE_PASTA) {
if (*netns) {
- ret = conf_ns_open(c, userns, netns);
- if (ret < 0)
- usage(argv[0]);
+ pasta_open_ns(c, userns, netns);
} else {
pasta_start_ns(c, argc - optind, argv + optind);
}
diff --git a/pasta.c b/pasta.c
index 0bdb655..0fd45e4 100644
--- a/pasta.c
+++ b/pasta.c
@@ -20,6 +20,7 @@
#include <stdio.h>
#include <string.h>
#include <errno.h>
+#include <libgen.h>
#include <limits.h>
#include <stdlib.h>
#include <stdint.h>
@@ -101,6 +102,71 @@ netns:
return 0;
}
+/**
+ * ns_check() - Check if we can enter configured namespaces
+ * @arg: Execution context
+ *
+ * Return: 0
+ */
+static int ns_check(void *arg)
+{
+ struct ctx *c = (struct ctx *)arg;
+
+ if ((!c->netns_only && setns(c->pasta_userns_fd, CLONE_NEWUSER)) ||
+ setns(c->pasta_netns_fd, CLONE_NEWNET))
+ c->pasta_userns_fd = c->pasta_netns_fd = -1;
+
+ return 0;
+
+}
+
+/**
+ * pasta_open_ns() - Open network, user namespaces descriptors
+ * @c: Execution context
+ * @userns: --userns argument, can be an empty string
+ * @netns: network namespace path
+ *
+ * Return: 0 on success, negative error code otherwise
+ */
+void pasta_open_ns(struct ctx *c, const char *userns, const char *netns)
+{
+ int ufd = -1, nfd = -1;
+
+ nfd = open(netns, O_RDONLY | O_CLOEXEC);
+ if (nfd < 0) {
+ err("Couldn't open network namespace %s", netns);
+ exit(EXIT_FAILURE);
+ }
+
+ if (!c->netns_only && *userns) {
+ ufd = open(userns, O_RDONLY | O_CLOEXEC);
+ if (ufd < 0) {
+ close(nfd);
+ err("Couldn't open user namespace %s", userns);
+ exit(EXIT_FAILURE);
+ }
+ }
+
+ c->pasta_netns_fd = nfd;
+ c->pasta_userns_fd = ufd;
+
+ NS_CALL(ns_check, c);
+
+ if (c->pasta_netns_fd < 0) {
+ err("Couldn't switch to pasta namespaces");
+ exit(EXIT_FAILURE);
+ }
+
+ if (!c->no_netns_quit) {
+ char buf[PATH_MAX] = { 0 };
+
+ strncpy(buf, netns, PATH_MAX - 1);
+ strncpy(c->netns_base, basename(buf), PATH_MAX - 1);
+ strncpy(buf, netns, PATH_MAX - 1);
+ strncpy(c->netns_dir, dirname(buf), PATH_MAX - 1);
+ }
+}
+
/**
* struct pasta_setup_ns_arg - Argument for pasta_setup_ns()
* @c: Execution context
diff --git a/pasta.h b/pasta.h
index 19b2e54..a1937b2 100644
--- a/pasta.h
+++ b/pasta.h
@@ -6,6 +6,7 @@
#ifndef PASTA_H
#define PASTA_H
+void pasta_open_ns(struct ctx *c, const char *userns, const char *netns);
void pasta_start_ns(struct ctx *c, int argc, char *argv[]);
void pasta_ns_conf(struct ctx *c);
void pasta_child_handler(int signal);
--
2.37.3
--netns-only is supposed to make pasta use only a network namespace, not a user namespace. However, pasta_start_ns() has this backwards, and if --netns-only is specified it creates a user namespace but *not* a network namespace. Correct this. Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au> --- pasta.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/pasta.c b/pasta.c index 0fd45e4..7eac8e9 100644 --- a/pasta.c +++ b/pasta.c @@ -244,8 +244,8 @@ void pasta_start_ns(struct ctx *c, int argc, char *argv[]) pasta_child_pid = clone(pasta_setup_ns, ns_fn_stack + sizeof(ns_fn_stack) / 2, - (c->netns_only ? 0 : CLONE_NEWNET) | - CLONE_NEWIPC | CLONE_NEWPID | CLONE_NEWUSER | + (c->netns_only ? 0 : CLONE_NEWUSER) | + CLONE_NEWIPC | CLONE_NEWPID | CLONE_NEWNET | CLONE_NEWUTS, (void *)&arg); -- 2.37.3
passt/pasta can interact with user namespaces in a number of ways:
1) With --netns-only we'll remain in our original user namespace
2) With --userns or a PID option to pasta we'll join either the given
user namespace or that of the PID
3) When pasta spawns a shell or command we'll start a new user namespace
for the command and then join it
4) With passt we'll create a new user namespace when we sandbox()
ourself
However (3) and (4) turn out to have essentially the same effect. In both
cases we create one new user namespace. The spawned command starts there,
and passt/pasta itself will live there from sandbox() onwards.
Because of this, we can simplify user namespace handling by moving the
userns handling earlier, to the same point we drop root in the original
namespace. Extend the drop_user() function to isolate_user() which does
both.
After switching UID and GID in the original userns, isolate_user() will
either join or create the userns we require. When we spawn a command with
pasta_start_ns()/pasta_setup_ns() we no longer need to create a userns,
because we're already made one. sandbox() likewise no longer needs to
create (or join) an userns because we're already in the one we need.
We no longer need c->pasta_userns_fd, since the fd is only used locally
in isolate_user(). Likewise we can replace c->netns_only with a local
in conf(), since it's not used outside there.
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
conf.c | 11 ++++----
isolation.c | 77 +++++++++++++++++++++++++++++++++++++++++------------
isolation.h | 2 +-
passt.c | 3 ++-
passt.h | 4 ---
pasta.c | 56 +++++---------------------------------
pasta.h | 2 +-
util.c | 5 ----
8 files changed, 77 insertions(+), 83 deletions(-)
diff --git a/conf.c b/conf.c
index 8477a6e..7f32859 100644
--- a/conf.c
+++ b/conf.c
@@ -1043,6 +1043,7 @@ static int conf_ugid(const char *runas, uid_t *uid, gid_t *gid)
*/
void conf(struct ctx *c, int argc, char **argv)
{
+ int netns_only = 0;
struct option options[] = {
{"debug", no_argument, NULL, 'd' },
{"quiet", no_argument, NULL, 'q' },
@@ -1077,7 +1078,7 @@ void conf(struct ctx *c, int argc, char **argv)
{"udp-ns", required_argument, NULL, 'U' },
{"userns", required_argument, NULL, 2 },
{"netns", required_argument, NULL, 3 },
- {"netns-only", no_argument, &c->netns_only, 1 },
+ {"netns-only", no_argument, &netns_only, 1 },
{"config-net", no_argument, &c->pasta_conf_ns, 1 },
{"ns-mac-addr", required_argument, NULL, 4 },
{"dhcp-dns", no_argument, NULL, 5 },
@@ -1515,22 +1516,22 @@ void conf(struct ctx *c, int argc, char **argv)
if (ret)
usage(argv[0]);
- drop_root(uid, gid);
-
if (c->mode == MODE_PASTA) {
- if (conf_pasta_ns(&c->netns_only, userns, netns,
+ if (conf_pasta_ns(&netns_only, userns, netns,
optind, argc, argv) < 0)
usage(argv[0]);
} else if (optind != argc) {
usage(argv[0]);
}
+ isolate_user(uid, gid, !netns_only, userns);
+
if (c->pasta_conf_ns)
c->no_ra = 1;
if (c->mode == MODE_PASTA) {
if (*netns) {
- pasta_open_ns(c, userns, netns);
+ pasta_open_ns(c, netns);
} else {
pasta_start_ns(c, argc - optind, argv + optind);
}
diff --git a/isolation.c b/isolation.c
index 41ca888..124dea4 100644
--- a/isolation.c
+++ b/isolation.c
@@ -20,6 +20,7 @@
#include <limits.h>
#include <pwd.h>
#include <sched.h>
+#include <stdbool.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
@@ -59,14 +60,19 @@ void drop_caps(void)
}
/**
- * drop_root() - Switch to given UID and GID
- * @uid: User ID to switch to
- * @gid: Group ID to switch to
+ * isolate_user() - Switch to final UID/GID and move into userns
+ * @uid: User ID to run as (in original userns)
+ * @gid: Group ID to run as (in original userns)
+ * @use_userns: Whether to join or create a userns
+ * @userns: userns path to enter, may be empty
*/
-void drop_root(uid_t uid, gid_t gid)
+void isolate_user(uid_t uid, gid_t gid, bool use_userns, const char *userns)
{
+ char nsmap[BUFSIZ];
+
+ /* First set our UID & GID in the original namespace */
if (setgroups(0, NULL)) {
- /* If we don't start with CAP_SETGID, this will EPERM */
+ /* If we don't have CAP_SETGID, this will EPERM */
if (errno != EPERM) {
err("Can't drop supplementary groups: %s",
strerror(errno));
@@ -74,11 +80,57 @@ void drop_root(uid_t uid, gid_t gid)
}
}
- if (!setgid(gid) && !setuid(uid))
+ if (setgid(gid) != 0) {
+ err("Can't set GID to %u: %s", gid, strerror(errno));
+ exit(EXIT_FAILURE);
+ }
+
+ if (setuid(uid) != 0) {
+ err("Can't set UID to %u: %s", uid, strerror(errno));
+ exit(EXIT_FAILURE);
+ }
+
+ /* If we're told not to use a userns, nothing more to do */
+ if (!use_userns)
+ return;
+
+ /* Otherwise, if given a userns, join it */
+ if (*userns) {
+ int ufd;
+
+ ufd = open(userns, O_RDONLY | O_CLOEXEC);
+ if (ufd < 0) {
+ err("Couldn't open user namespace %s: %s",
+ userns, strerror(errno));
+ exit(EXIT_FAILURE);
+ }
+
+ if (setns(ufd, CLONE_NEWUSER) != 0) {
+ err("Couldn't enter user namespace %s: %s",
+ userns, strerror(errno));
+ exit(EXIT_FAILURE);
+ }
+
+ close(ufd);
+
return;
+ }
- err("Can't change user/group, exiting");
- exit(EXIT_FAILURE);
+ /* Otherwise, create our own userns */
+ if (unshare(CLONE_NEWUSER) != 0) {
+ err("Couldn't create user namespace: %s", strerror(errno));
+ exit(EXIT_FAILURE);
+ }
+
+ /* Configure user and group mappings */
+ snprintf(nsmap, BUFSIZ, "0 %u 1", uid);
+ FWRITE("/proc/self/uid_map", nsmap, "Cannot set uid_map in
namespace");
+
+ FWRITE("/proc/self/setgroups", "deny",
+ "Cannot write to setgroups in namespace");
+
+ snprintf(nsmap, BUFSIZ, "0 %u 1", gid);
+ FWRITE("/proc/self/gid_map", nsmap, "Cannot set gid_map in
namespace");
}
/**
@@ -90,15 +142,6 @@ int sandbox(struct ctx *c)
{
int flags = CLONE_NEWIPC | CLONE_NEWNS | CLONE_NEWUTS;
- if (!c->netns_only) {
- if (c->pasta_userns_fd == -1)
- flags |= CLONE_NEWUSER;
- else
- setns(c->pasta_userns_fd, CLONE_NEWUSER);
- }
-
- c->pasta_userns_fd = -1;
-
/* If we run in foreground, we have no chance to actually move to a new
* PID namespace. For passt, use CLONE_NEWPID anyway, in case somebody
* ever gets around seccomp profiles -- there's no harm in passing it.
diff --git a/isolation.h b/isolation.h
index 2540a35..2c73df7 100644
--- a/isolation.h
+++ b/isolation.h
@@ -8,7 +8,7 @@
#define ISOLATION_H
void drop_caps(void);
-void drop_root(uid_t uid, gid_t gid);
+void isolate_user(uid_t uid, gid_t gid, bool use_userns, const char *userns);
int sandbox(struct ctx *c);
void seccomp(const struct ctx *c);
diff --git a/passt.c b/passt.c
index 2a8314c..f0ed897 100644
--- a/passt.c
+++ b/passt.c
@@ -23,6 +23,7 @@
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/resource.h>
+#include <stdbool.h>
#include <stdlib.h>
#include <unistd.h>
#include <netdb.h>
@@ -185,7 +186,7 @@ int main(int argc, char **argv)
drop_caps();
- c.pasta_userns_fd = c.pasta_netns_fd = c.fd_tap = c.fd_tap_listen = -1;
+ c.pasta_netns_fd = c.fd_tap = c.fd_tap_listen = -1;
sigemptyset(&sa.sa_mask);
sa.sa_flags = 0;
diff --git a/passt.h b/passt.h
index 3035430..8c8d710 100644
--- a/passt.h
+++ b/passt.h
@@ -145,8 +145,6 @@ struct ip6_ctx {
* @pcap: Path for packet capture file
* @pid_file: Path to PID file, empty string if not configured
* @pasta_netns_fd: File descriptor for network namespace in pasta mode
- * @pasta_userns_fd: Descriptor for user namespace to join, -1 once joined
- * @netns_only: In pasta mode, don't join or create a user namespace
* @no_netns_quit: In pasta mode, don't exit if fs-bound namespace is gone
* @netns_base: Base name for fs-bound namespace, if any, in pasta mode
* @netns_dir: Directory of fs-bound namespace, if any, in pasta mode
@@ -197,8 +195,6 @@ struct ctx {
char pid_file[PATH_MAX];
int pasta_netns_fd;
- int pasta_userns_fd;
- int netns_only;
int no_netns_quit;
char netns_base[PATH_MAX];
diff --git a/pasta.c b/pasta.c
index 7eac8e9..e233762 100644
--- a/pasta.c
+++ b/pasta.c
@@ -23,6 +23,7 @@
#include <libgen.h>
#include <limits.h>
#include <stdlib.h>
+#include <stdbool.h>
#include <stdint.h>
#include <unistd.h>
#include <syslog.h>
@@ -83,16 +84,6 @@ static int pasta_wait_for_ns(void *arg)
int flags = O_RDONLY | O_CLOEXEC;
char ns[PATH_MAX];
- if (c->netns_only)
- goto netns;
-
- snprintf(ns, PATH_MAX, "/proc/%i/ns/user", pasta_child_pid);
- do
- while ((c->pasta_userns_fd = open(ns, flags)) < 0);
- while (setns(c->pasta_userns_fd, CLONE_NEWUSER) &&
- !close(c->pasta_userns_fd));
-
-netns:
snprintf(ns, PATH_MAX, "/proc/%i/ns/net", pasta_child_pid);
do
while ((c->pasta_netns_fd = open(ns, flags)) < 0);
@@ -112,25 +103,23 @@ static int ns_check(void *arg)
{
struct ctx *c = (struct ctx *)arg;
- if ((!c->netns_only && setns(c->pasta_userns_fd, CLONE_NEWUSER)) ||
- setns(c->pasta_netns_fd, CLONE_NEWNET))
- c->pasta_userns_fd = c->pasta_netns_fd = -1;
+ if (setns(c->pasta_netns_fd, CLONE_NEWNET))
+ c->pasta_netns_fd = -1;
return 0;
}
/**
- * pasta_open_ns() - Open network, user namespaces descriptors
+ * pasta_open_ns() - Open network namespace descriptors
* @c: Execution context
- * @userns: --userns argument, can be an empty string
* @netns: network namespace path
*
* Return: 0 on success, negative error code otherwise
*/
-void pasta_open_ns(struct ctx *c, const char *userns, const char *netns)
+void pasta_open_ns(struct ctx *c, const char *netns)
{
- int ufd = -1, nfd = -1;
+ int nfd = -1;
nfd = open(netns, O_RDONLY | O_CLOEXEC);
if (nfd < 0) {
@@ -138,17 +127,7 @@ void pasta_open_ns(struct ctx *c, const char *userns, const char
*netns)
exit(EXIT_FAILURE);
}
- if (!c->netns_only && *userns) {
- ufd = open(userns, O_RDONLY | O_CLOEXEC);
- if (ufd < 0) {
- close(nfd);
- err("Couldn't open user namespace %s", userns);
- exit(EXIT_FAILURE);
- }
- }
-
c->pasta_netns_fd = nfd;
- c->pasta_userns_fd = ufd;
NS_CALL(ns_check, c);
@@ -169,12 +148,9 @@ void pasta_open_ns(struct ctx *c, const char *userns, const char
*netns)
/**
* struct pasta_setup_ns_arg - Argument for pasta_setup_ns()
- * @c: Execution context
- * @euid: Effective UID of caller
+ * @argv: Command and arguments to run
*/
struct pasta_setup_ns_arg {
- struct ctx *c;
- int euid;
char **argv;
};
@@ -188,21 +164,6 @@ static int pasta_setup_ns(void *arg)
{
struct pasta_setup_ns_arg *a = (struct pasta_setup_ns_arg *)arg;
- if (!a->c->netns_only) {
- char buf[BUFSIZ];
-
- snprintf(buf, BUFSIZ, "%i %i %i", 0, a->euid, 1);
-
- FWRITE("/proc/self/uid_map", buf,
- "Cannot set uid_map in namespace");
-
- FWRITE("/proc/self/setgroups", "deny",
- "Cannot write to setgroups in namespace");
-
- FWRITE("/proc/self/gid_map", buf,
- "Cannot set gid_map in namespace");
- }
-
FWRITE("/proc/sys/net/ipv4/ping_group_range", "0 0",
"Cannot set ping_group_range, ICMP requests might fail");
@@ -221,8 +182,6 @@ static int pasta_setup_ns(void *arg)
void pasta_start_ns(struct ctx *c, int argc, char *argv[])
{
struct pasta_setup_ns_arg arg = {
- .c = c,
- .euid = geteuid(),
.argv = argv,
};
char *shell = getenv("SHELL") ? getenv("SHELL") :
"/bin/sh";
@@ -244,7 +203,6 @@ void pasta_start_ns(struct ctx *c, int argc, char *argv[])
pasta_child_pid = clone(pasta_setup_ns,
ns_fn_stack + sizeof(ns_fn_stack) / 2,
- (c->netns_only ? 0 : CLONE_NEWUSER) |
CLONE_NEWIPC | CLONE_NEWPID | CLONE_NEWNET |
CLONE_NEWUTS,
(void *)&arg);
diff --git a/pasta.h b/pasta.h
index a1937b2..02df1f6 100644
--- a/pasta.h
+++ b/pasta.h
@@ -6,7 +6,7 @@
#ifndef PASTA_H
#define PASTA_H
-void pasta_open_ns(struct ctx *c, const char *userns, const char *netns);
+void pasta_open_ns(struct ctx *c, const char *netns);
void pasta_start_ns(struct ctx *c, int argc, char *argv[]);
void pasta_ns_conf(struct ctx *c);
void pasta_child_handler(int signal);
diff --git a/util.c b/util.c
index f709838..8d26561 100644
--- a/util.c
+++ b/util.c
@@ -464,11 +464,6 @@ void procfs_scan_listen(struct ctx *c, uint8_t proto, int ip_version,
int ns,
*/
int ns_enter(const struct ctx *c)
{
- if (!c->netns_only &&
- c->pasta_userns_fd != -1 &&
- setns(c->pasta_userns_fd, CLONE_NEWUSER))
- exit(EXIT_FAILURE);
-
if (setns(c->pasta_netns_fd, CLONE_NEWNET))
exit(EXIT_FAILURE);
--
2.37.3
Currently --userns is only allowed when pasta is attaching to an existing
netns or PID, and is prohibited when creating a new netns by spawning a
command or shell.
With the new handling of userns, this check isn't neccessary. I'm not sure
if there's any use case for --userns with a spawned command, but it's
strictly more flexible and requires zero extra code, so we might as well.
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
conf.c | 5 -----
passt.1 | 2 --
2 files changed, 7 deletions(-)
diff --git a/conf.c b/conf.c
index 7f32859..d80233c 100644
--- a/conf.c
+++ b/conf.c
@@ -561,11 +561,6 @@ static int conf_pasta_ns(int *netns_only, char *userns, char *netns,
}
}
- if (*userns && !*netns) {
- err("--userns requires --netns or PID");
- return -EINVAL;
- }
-
/* Attaching to a netns/PID, with no userns given */
if (*netns && !*userns)
*netns_only = 1;
diff --git a/passt.1 b/passt.1
index 88cc879..83395bc 100644
--- a/passt.1
+++ b/passt.1
@@ -453,8 +453,6 @@ Default is \fBauto\fR.
Target user namespace to join, as a path. If PID is given, without this option,
the user namespace will be the one of the corresponding process.
-This option requires --netns or a PID to be specified.
-
.TP
.BR \-\-netns " " \fIspec
Target network namespace to join, as a path or a name. A name is treated as
--
2.37.3