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[1/2] apparmor: shift ouid when mediating hard links in userns

Message ID 20250416224209.904863-1-gabriel.totev@zetier.com (mailing list archive)
State New
Headers show
Series [1/2] apparmor: shift ouid when mediating hard links in userns | expand

Commit Message

Gabriel Totev April 16, 2025, 10:42 p.m. UTC 
When using AppArmor profiles inside an unprivileged container,
the link operation observes an unshifted ouid.
(tested with LXD and Incus)

For example, root inside container and uid 1000000 outside, with
`owner /root/link l,` profile entry for ln:

/root$ touch chain && ln chain link
==> dmesg
apparmor="DENIED" operation="link" class="file"
namespace="root//lxd-feet_<var-snap-lxd-common-lxd>" profile="linkit"
name="/root/link" pid=1655 comm="ln" requested_mask="l" denied_mask="l"
fsuid=1000000 ouid=0 [<== should be 1000000] target="/root/chain"

Fix by mapping inode uid of old_dentry in aa_path_link() rather than
using it directly, similarly to how it's mapped in __file_path_perm()
later in the file.

Signed-off-by: Gabriel Totev <gabriel.totev@zetier.com>
---
 security/apparmor/file.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/security/apparmor/file.c b/security/apparmor/file.c
index 5c984792cbf0..ecd36199337c 100644
--- a/security/apparmor/file.c
+++ b/security/apparmor/file.c
@@ -430,9 +430,11 @@  int aa_path_link(const struct cred *subj_cred,
 {
 	struct path link = { .mnt = new_dir->mnt, .dentry = new_dentry };
 	struct path target = { .mnt = new_dir->mnt, .dentry = old_dentry };
+	struct inode *inode = d_backing_inode(old_dentry);
+	vfsuid_t vfsuid = i_uid_into_vfsuid(mnt_idmap(target.mnt), inode);
 	struct path_cond cond = {
-		d_backing_inode(old_dentry)->i_uid,
-		d_backing_inode(old_dentry)->i_mode
+		.uid = vfsuid_into_kuid(vfsuid),
+		.mode = inode->i_mode,
 	};
 	char *buffer = NULL, *buffer2 = NULL;
 	struct aa_profile *profile;