If a parent accidentally or due to implementation reasons leaks any
open file, we don't want to have access to them, except for the file
passed via --fd, if any.
This is the case for Podman when Podman's parent leaks files into
Podman: it's not practical for Podman to close unrelated files before
starting pasta, as reported by Paul.
Use close_range(2) to close all open files except for standard streams
and the one from --fd.
Given that parts of conf() depend on other files to be already opened,
such as the epoll file descriptor, we can't easily defer this to a
more convenient point, where --fd was already parsed. Introduce a
minimal, duplicate version of --fd parsing to keep this simple.
As we need to check that the passed --fd option doesn't exceed
INT_MAX, because we'll parse it with strtol() but file descriptor
indices are signed ints (regardless of the arguments close_range()
take), extend the existing check in the actual --fd parsing in conf(),
also rejecting file descriptors numbers that match standard streams,
while at it.
Suggested-by: Paul Holzinger <pholzing(a)redhat.com>
Signed-off-by: Stefano Brivio <sbrivio(a)redhat.com>
---
v7: (yes, seriously) don't close STDERR_FILENO in the general case,
start from STDERR_FILENO + 1
v6: (seriously?) fix STDERR_FILENO comparison in conf()
v5: Reject any --fd matching standard streams
v4: c->fd_tap, as used in conf(), is an int: don't assign to it
directly from strtol(), or we won't catch overflows
v3: Handle --fd 3 case, and don't overflow if the --fd number exceeds
UINT_MAX: add an explicit check to ensure it's less than INT_MAX
v2: Move call to close_open_files() to isolate_initial()
conf.c | 8 ++++++--
isolation.c | 12 +++++++++---
isolation.h | 2 +-
passt.c | 2 +-
util.c | 41 +++++++++++++++++++++++++++++++++++++++++
util.h | 1 +
6 files changed, 59 insertions(+), 7 deletions(-)
diff --git a/conf.c b/conf.c
index 14d8ece..2f5d649 100644
--- a/conf.c
+++ b/conf.c
@@ -1245,6 +1245,7 @@ void conf(struct ctx *c, int argc, char **argv)
const char *optstring;
size_t logsize = 0;
char *runas = NULL;
+ long fd_tap_opt;
int name, ret;
uid_t uid;
gid_t gid;
@@ -1260,6 +1261,7 @@ void conf(struct ctx *c, int argc, char **argv)
c->tcp.fwd_in.mode = c->tcp.fwd_out.mode = FWD_UNSET;
c->udp.fwd_in.mode = c->udp.fwd_out.mode = FWD_UNSET;
+ optind = 1;
do {
name = getopt_long(argc, argv, optstring, options, NULL);
@@ -1424,11 +1426,13 @@ void conf(struct ctx *c, int argc, char **argv)
break;
case 'F':
errno = 0;
- c->fd_tap = strtol(optarg, NULL, 0);
+ fd_tap_opt = strtol(optarg, NULL, 0);
- if (c->fd_tap < 0 || errno)
+ if (errno ||
+ fd_tap_opt <= STDERR_FILENO || fd_tap_opt > INT_MAX)
die("Invalid --fd: %s", optarg);
+ c->fd_tap = fd_tap_opt;
c->one_off = true;
*c->sock_path = 0;
break;
diff --git a/isolation.c b/isolation.c
index 4956d7e..45fba1e 100644
--- a/isolation.c
+++ b/isolation.c
@@ -29,7 +29,8 @@
*
* Executed immediately after startup, drops capabilities we don't
* need at any point during execution (or which we gain back when we
- * need by joining other namespaces).
+ * need by joining other namespaces), and closes any leaked file we
+ * might have inherited from the parent process.
*
* 2. isolate_user()
* =================
@@ -166,14 +167,17 @@ static void clamp_caps(void)
}
/**
- * isolate_initial() - Early, config independent self isolation
+ * isolate_initial() - Early, mostly config independent self isolation
+ * @argc: Argument count
+ * @argv: Command line options: only --fd (if present) is relevant here
*
* Should:
* - drop unneeded capabilities
+ * - close all open files except for standard streams and the one from --fd
* Musn't:
* - remove filesytem access (we need to access files during setup)
*/
-void isolate_initial(void)
+void isolate_initial(int argc, char **argv)
{
uint64_t keep;
@@ -207,6 +211,8 @@ void isolate_initial(void)
keep |= BIT(CAP_SETFCAP) | BIT(CAP_SYS_PTRACE);
drop_caps_ep_except(keep);
+
+ close_open_files(argc, argv);
}
/**
diff --git a/isolation.h b/isolation.h
index 846b2af..80bb68d 100644
--- a/isolation.h
+++ b/isolation.h
@@ -7,7 +7,7 @@
#ifndef ISOLATION_H
#define ISOLATION_H
-void isolate_initial(void);
+void isolate_initial(int argc, char **argv);
void isolate_user(uid_t uid, gid_t gid, bool use_userns, const char *userns,
enum passt_modes mode);
int isolate_prefork(const struct ctx *c);
diff --git a/passt.c b/passt.c
index ea5bece..4b3c306 100644
--- a/passt.c
+++ b/passt.c
@@ -211,7 +211,7 @@ int main(int argc, char **argv)
arch_avx2_exec(argv);
- isolate_initial();
+ isolate_initial(argc, argv);
c.pasta_netns_fd = c.fd_tap = c.pidfile_fd = -1;
diff --git a/util.c b/util.c
index 07fb21c..7761bd3 100644
--- a/util.c
+++ b/util.c
@@ -26,6 +26,7 @@
#include <errno.h>
#include <stdbool.h>
#include <linux/errqueue.h>
+#include <getopt.h>
#include "util.h"
#include "iov.h"
@@ -694,3 +695,43 @@ const char *str_ee_origin(const struct sock_extended_err *ee)
return "<invalid>";
}
+
+/**
+ * close_open_files() - Close leaked files, but not --fd, stdin, stdout, stderr
+ * @argc: Argument count
+ * @argv: Command line options, as we need to skip any file given via --fd
+ */
+void close_open_files(int argc, char **argv)
+{
+ const struct option optfd[] = { { "fd", required_argument, NULL, 'F' },
+ { 0 },
+ };
+ long fd = -1;
+ int name, rc;
+
+ do {
+ name = getopt_long(argc, argv, ":F", optfd, NULL);
+
+ if (name == 'F') {
+ errno = 0;
+ fd = strtol(optarg, NULL, 0);
+
+ if (errno || fd <= STDERR_FILENO || fd > INT_MAX)
+ die("Invalid --fd: %s", optarg);
+ }
+ } while (name != -1);
+
+ if (fd == -1) {
+ rc = close_range(STDERR_FILENO + 1, ~0U, CLOSE_RANGE_UNSHARE);
+ } else if (fd == STDERR_FILENO + 1) { /* Still a single range */
+ rc = close_range(STDERR_FILENO + 2, ~0U, CLOSE_RANGE_UNSHARE);
+ } else {
+ rc = close_range(STDERR_FILENO + 1, fd - 1,
+ CLOSE_RANGE_UNSHARE);
+ if (!rc)
+ rc = close_range(fd + 1, ~0U, CLOSE_RANGE_UNSHARE);
+ }
+
+ if (rc)
+ die_perror("Failed to close files leaked by parent");
+}
diff --git a/util.h b/util.h
index 83d2b53..cb4d181 100644
--- a/util.h
+++ b/util.h
@@ -183,6 +183,7 @@ int __daemon(int pidfile_fd, int devnull_fd);
int fls(unsigned long x);
int write_file(const char *path, const char *buf);
int write_remainder(int fd, const struct iovec *iov, size_t iovcnt, size_t skip);
+void close_open_files(int argc, char **argv);
/**
* af_name() - Return name of an address family
--
2.43.0