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