Re: [PATCH 1/2] apparmor: shift ouid when mediating hard links in userns
From: John Johansen <john.johansen@canonical.com>
Date: 2025-05-17 08:40:37
On 4/16/25 15:42, Gabriel Totev wrote:
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.
so unfortunately this isn't correct. Yes some mapping needs to be done but it needs to be relative to different policy namespaces. I need to spend some time on this
quoted hunk ↗ jump to hunk
Signed-off-by: Gabriel Totev <redacted> --- security/apparmor/file.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)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;