[SRU][J/N/P][PATCH 2/2] apparmor: shift uid when mediating af_unix in userns

[Wesley Hershberger]

From: Gabriel Totev <gabriel.totev at zetier.com>

BugLink: https://bugs.launchpad.net/bugs/2121257

Avoid unshifted ouids for socket file operations as observed when using
AppArmor profiles in unprivileged containers with LXD or Incus.

For example, root inside container and uid 1000000 outside, with
`owner /root/sock rw,` profile entry for nc:

/root$ nc -lkU sock & nc -U sock
==> dmesg
apparmor="DENIED" operation="connect" class="file"
namespace="root//lxd-podia_<var-snap-lxd-common-lxd>" profile="sockit"
name="/root/sock" pid=3924 comm="nc" requested_mask="wr" denied_mask="wr"
fsuid=1000000 ouid=0 [<== should be 1000000]

Fix by performing uid mapping as per common_perm_cond() in lsm.c

Signed-off-by: Gabriel Totev <gabriel.totev at zetier.com>
Fixes: c05e705812d1 ("apparmor: add fine grained af_unix mediation")
Signed-off-by: John Johansen <john.johansen at canonical.com>
(backported from commit 3fa0af4cc8a31d4139ee85a7b0e3d9b4f37b3093)
[whershberger: u->path to path from missing bc6e5f693]
Signed-off-by: Wesley Hershberger <wesley.hershberger at canonical.com>
---
 security/apparmor/af_unix.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/security/apparmor/af_unix.c b/security/apparmor/af_unix.c
index c036bbba814f..9a6ae7b2cf2e 100644
--- a/security/apparmor/af_unix.c
+++ b/security/apparmor/af_unix.c
@@ -12,6 +12,7 @@
  * License.
  */
 
+#include <linux/fs.h>
 #include <net/tcp_states.h>
 
 #include "include/audit.h"
@@ -45,8 +46,11 @@ static int unix_fs_perm(const char *op, u32 mask, const struct cred *subj_cred,
 	 */
 	if (u->path.dentry) {
 		/* the sunpath may not be valid for this ns so use the path */
-		struct path_cond cond = { u->path.dentry->d_inode->i_uid,
-					  u->path.dentry->d_inode->i_mode
+		struct inode *inode = u->path.dentry->d_inode;
+		vfsuid_t vfsuid = i_uid_into_vfsuid(mnt_idmap(u->path.mnt), inode);
+		struct path_cond cond = {
+			.uid = vfsuid_into_kuid(vfsuid),
+			.mode = inode->i_mode,
 		};
 
 		return aa_path_perm(op, subj_cred, label, &u->path,
-- 
2.43.0