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libmount: improve X-mount.mkdir for non-root users 

Since v2.35 mount(8) drops suid on -EPERM and repeat necessary actions
before mount(2) syscall. This patch also improves this behavior for
X-mount.mkdir too.

mount(8):
 * return -EPERM on sanitize_paths() rather than call err()
 * call suid_drop() on failed sanitize_paths()
 * update man page

libmount:
 * mnt_context_prepare_target() refactoring
 * return -EPERM when in restricted mode for X-mount.mkdir

Fixed version:
 /home/kzak/mnt-foo   sr.net.home:/home/kzak   fuse.sshfs noauto,X-mount.mkdir

 $ mount /home/kzak/mnt-foo
 kzak@sr.net.home's password:

 $ /home/projects/util-linux/util-linux  findmnt /home/kzak/mnt-foo
 TARGET             SOURCE                 FSTYPE     OPTIONS
 /home/kzak/mnt-foo sr.net.home:/home/kzak fuse.sshfs rw,nosuid,nodev,relatime,user_id=1000,group_id=1000

Addresses: https://github.com/systemd/systemd/issues/14418
Signed-off-by: Karel Zak <kzak@redhat.com>
This commit is contained in:
Karel Zak 2020-01-03 10:48:09 +01:00
parent d0c4300682
commit 6b0094d0c1
4 changed files with 29 additions and 30 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

37
libmount/src/context.c
View File

@ -1903,7 +1903,6 @@ static int mkdir_target(const char *tgt, struct libmnt_fs *fs)
int mnt_context_prepare_target(struct libmnt_context *cxt)
{
const char *tgt, *prefix;
struct libmnt_cache *cache;
int rc = 0;
struct libmnt_ns *ns_old;
@ -1944,37 +1943,35 @@ int mnt_context_prepare_target(struct libmnt_context *cxt)
if (!ns_old)
return -MNT_ERR_NAMESPACE;
/* mkdir target */
/* X-mount.mkdir target */
if (cxt->action == MNT_ACT_MOUNT
&& !mnt_context_is_restricted(cxt)
&& (cxt->user_mountflags & MNT_MS_XCOMMENT ||
cxt->user_mountflags & MNT_MS_XFSTABCOMM)) {
rc = mkdir_target(tgt, cxt->fs);
if (rc) {
if (!mnt_context_switch_ns(cxt, ns_old))
return -MNT_ERR_NAMESPACE;
return rc; /* mkdir or parse error */
}
/* supported only for root or non-suid mount(8) */
if (!mnt_context_is_restricted(cxt))
rc = mkdir_target(tgt, cxt->fs);
else
rc = -EPERM;
}
/* canonicalize the path */
cache = mnt_context_get_cache(cxt);
if (cache) {
char *path = mnt_resolve_path(tgt, cache);
if (path && strcmp(path, tgt) != 0)
rc = mnt_fs_set_target(cxt->fs, path);
if (rc == 0) {
struct libmnt_cache *cache = mnt_context_get_cache(cxt);
if (cache) {
char *path = mnt_resolve_path(tgt, cache);
if (path && strcmp(path, tgt) != 0)
rc = mnt_fs_set_target(cxt->fs, path);
}
}
if (!mnt_context_switch_ns(cxt, ns_old))
return -MNT_ERR_NAMESPACE;
if (rc)
DBG(CXT, ul_debugobj(cxt, "failed to prepare target '%s'", tgt));
else
DBG(CXT, ul_debugobj(cxt, "final target '%s'",
mnt_fs_get_target(cxt->fs)));
return 0;
DBG(CXT, ul_debugobj(cxt, "final target '%s' [rc=%d]",
mnt_fs_get_target(cxt->fs), rc));
return rc;
}
/* Guess type, but not set to cxt->fs, always use free() for the result. It's

4
libmount/src/context_mount.c
View File

@ -992,10 +992,10 @@ int mnt_context_prepare_mount(struct libmnt_context *cxt)
rc = fix_optstr(cxt);
if (!rc)
rc = mnt_context_prepare_srcpath(cxt);
if (!rc)
rc = mnt_context_prepare_target(cxt);
if (!rc)
rc = mnt_context_guess_fstype(cxt);
if (!rc)
rc = mnt_context_prepare_target(cxt);
if (!rc)
rc = mnt_context_prepare_helper(cxt, "mount", NULL);
if (rc) {

5
sys-utils/mount.8
View File

@ -1311,8 +1311,9 @@ Allow to make a target directory (mountpoint). The optional argument
specifies the filesystem access mode used for
.BR mkdir (2)
in octal notation. The default mode is 0755. This functionality is supported
only for root users. The option is also supported as x-mount.mkdir, this notation
is deprecated for mount.mkdir since v2.30.
only for root users or when mount executed without suid permissions. The option
is also supported as x-mount.mkdir, this notation is deprecated for mount.mkdir
since v2.30.
.SH "FILESYSTEM-SPECIFIC MOUNT OPTIONS"
You should consult the respective man page for the filesystem first.

13
sys-utils/mount.c
View File

@ -384,19 +384,19 @@ static struct libmnt_table *append_fstab(struct libmnt_context *cxt,
* Check source and target paths -- non-root user should not be able to
* resolve paths which are unreadable for him.
*/
static void sanitize_paths(struct libmnt_context *cxt)
static int sanitize_paths(struct libmnt_context *cxt)
{
const char *p;
struct libmnt_fs *fs = mnt_context_get_fs(cxt);
if (!fs)
return;
return 0;
p = mnt_fs_get_target(fs);
if (p) {
char *np = canonicalize_path_restricted(p);
if (!np)
err(MNT_EX_USAGE, "%s", p);
return -EPERM;
mnt_fs_set_target(fs, np);
free(np);
}
@ -405,10 +405,11 @@ static void sanitize_paths(struct libmnt_context *cxt)
if (p) {
char *np = canonicalize_path_restricted(p);
if (!np)
err(MNT_EX_USAGE, "%s", p);
return -EPERM;
mnt_fs_set_source(fs, np);
free(np);
}
return 0;
}
static void append_option(struct libmnt_context *cxt, const char *opt)
@ -952,8 +953,8 @@ int main(int argc, char **argv)
errtryhelp(MNT_EX_USAGE);
}
if (mnt_context_is_restricted(cxt))
sanitize_paths(cxt);
if (mnt_context_is_restricted(cxt) && sanitize_paths(cxt) != 0)
suid_drop(cxt);
if (is_move)
/* "move" as option string is not supported by libmount */