Hi,
the mount command does not work properly if you replace suid with
POSIX file capabilities. We still need to check for non-root mounts and
the command has to work in very restricted mode for non-root users.
See the patch below. The author of the patch is Geoff Johnstone.
The patch allows you to remove suid bit from mount and umount. Note
that you need a system with filesystem capability support, e.g.
Fedora 10).
# ls -l /bin/mount
-rwxr-xr-x 1 root root 65192 2008-11-09 22:59 /bin/mount
# getcap /bin/mount
/bin/mount = cap_dac_override,cap_sys_admin+ep
If anyone has any objections, please let me know.
Karel
Don't bypass security checks when [u]mount uses POSIX file capabilities
rather than setuid root to permit non-root mounts.
Signed-off-by: Geoff Johnstone <geoff.johnstone@xxxxxxxxxxxxxx>
---
diff --git a/mount/mount.c b/mount/mount.c
index f92b23c..23f27d6 100644
--- a/mount/mount.c
+++ b/mount/mount.c
@@ -80,8 +80,8 @@ static int list_with_volumelabel = 0;
*/
static int mounttype = 0;
-/* True if ruid != euid. */
-static int suid = 0;
+/* True if (ruid != euid) or (0 != ruid), i.e. only "user" mounts permitted. */
+static int restricted = 1;
/* Contains the fd to read the passphrase from, if any. */
static int pfd = -1;
@@ -774,12 +774,12 @@ guess_fstype_and_mount(const char *spec, const char *node, const char **types,
}
/*
- * suid_check()
+ * restricted_check()
* Die if the user is not allowed to do this.
*/
static void
-suid_check(const char *spec, const char *node, int *flags, char **user) {
- if (suid) {
+restricted_check(const char *spec, const char *node, int *flags, char **user) {
+ if (restricted) {
/*
* MS_OWNER: Allow owners to mount when fstab contains
* the owner option. Note that this should never be used
@@ -1109,7 +1109,7 @@ try_mount_one (const char *spec0, const char *node0, const char *types0,
if (mount_all && (flags & MS_NOAUTO))
goto out;
- suid_check(spec, node, &flags, &user);
+ restricted_check(spec, node, &flags, &user);
/* The "mount -f" checks for for existing record in /etc/mtab (with
* regular non-fake mount this is usually done by kernel)
@@ -1190,7 +1190,7 @@ mount_retry:
/* Mount failed, complain, but don't die. */
if (types == 0) {
- if (suid)
+ if (restricted)
error (_("mount: I could not determine the filesystem type, "
"and none was specified"));
else
@@ -2027,11 +2027,20 @@ main(int argc, char *argv[]) {
return print_all (types);
}
- if (getuid () != geteuid ()) {
- suid = 1;
- if (types || options || readwrite || nomtab || mount_all ||
- fake || mounttype || (argc + specseen) != 1)
- die (EX_USAGE, _("mount: only root can do that"));
+ {
+ const uid_t ruid = getuid();
+ const uid_t euid = geteuid();
+
+ /* if we're really root and aren't running setuid */
+ if (((uid_t)0 == ruid) && (ruid == euid)) {
+ restricted = 0;
+ }
+ }
+
+ if (restricted &&
+ (types || options || readwrite || nomtab || mount_all ||
+ fake || mounttype || (argc + specseen) != 1)) {
+ die (EX_USAGE, _("mount: only root can do that"));
}
atexit(unlock_mtab);
diff --git a/mount/umount.c b/mount/umount.c
index 81f8bdf..246bdd7 100644
--- a/mount/umount.c
+++ b/mount/umount.c
@@ -74,8 +74,8 @@ int nomtab = 0;
/* Call losetup -d for each unmounted loop device. */
int delloop = 0;
-/* True if ruid != euid. */
-int suid = 0;
+/* True if (ruid != euid) or (0 != ruid), i.e. only "user" umounts permitted. */
+int restricted = 1;
/* Last error message */
int complained_err = 0;
@@ -477,7 +477,7 @@ umount_file (char *arg) {
if (!mc && verbose)
printf(_("Could not find %s in mtab\n"), file);
- if (suid) {
+ if (restricted) {
char *mtab_user = NULL;
if (!mc)
@@ -640,10 +640,18 @@ main (int argc, char *argv[]) {
usage (stderr, 1);
}
- if (getuid () != geteuid ()) {
- suid = 1;
- if (all || types || nomtab || force || remount)
- die (2, _("umount: only root can do that"));
+ {
+ const uid_t ruid = getuid();
+ const uid_t euid = geteuid();
+
+ /* if we're really root and aren't running setuid */
+ if (((uid_t)0 == ruid) && (ruid == euid)) {
+ restricted = 0;
+ }
+ }
+
+ if (restricted && (all || types || nomtab || force || remount)) {
+ die (2, _("umount: only root can do that"));
}
argc -= optind;
--
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