apparmor: Fix move_mount mediation by detecting if source is detached

Prevent move_mount from applying the attach_disconnected flag
to move_mount(). This prevents detached mounts from appearing
as / when applying mount mediation, which is not only incorrect
but could result in bad policy being generated.

Basic mount rules like
  allow mount,
  allow mount options=(move) -> /target/,

will allow detached mounts, allowing older policy to continue
to function. New policy gains the ability to specify `detached` as
a source option
  allow mount detached -> /target/,

In addition make sure support of move_mount is advertised as
a feature to userspace so that applications that generate policy
can respond to the addition.

Note: this fixes mediation of move_mount when a detached mount is used,
      it does not fix the broader regression of apparmor mediation of
      mounts under the new mount api.

Link: https://lore.kernel.org/all/68c166b8-5b4d-4612-8042-1dee3334385b@leemhuis.info/T/#mb35fdde37f999f08f0b02d58dc1bf4e6b65b8da2
Fixes: 157a3537d6bc ("apparmor: Fix regression in mount mediation")
Reviewed-by: Georgia Garcia <georgia.garcia@canonical.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

diff --git a/security/apparmor/apparmorfs.c b/security/apparmor/apparmorfs.c
index 38650e52ef57872429823462df9000aded787292..2d9f2a4b451996a25b4d5c9797ebc73eac5739f8 100644 (file)
--- a/security/apparmor/apparmorfs.c
+++ b/security/apparmor/apparmorfs.c
@@ -2373,6 +2373,7 @@ static struct aa_sfs_entry aa_sfs_entry_policy[] = {
 
 static struct aa_sfs_entry aa_sfs_entry_mount[] = {
        AA_SFS_FILE_STRING("mask", "mount umount pivot_root"),
+       AA_SFS_FILE_STRING("move_mount", "detached"),
        { }
 };
 

diff --git a/security/apparmor/mount.c b/security/apparmor/mount.c
index fb30204c761ad92176b74ce1be8d5bc757787302..49fe8da6fea4597399f1b2113f230353a8b8c674 100644 (file)
--- a/security/apparmor/mount.c
+++ b/security/apparmor/mount.c
@@ -499,6 +499,10 @@ int aa_move_mount(const struct cred *subj_cred,
        error = -ENOMEM;
        if (!to_buffer || !from_buffer)
                goto out;
+
+       if (!our_mnt(from_path->mnt))
+               /* moving a mount detached from the namespace */
+               from_path = NULL;
        error = fn_for_each_confined(label, profile,
                        match_mnt(subj_cred, profile, to_path, to_buffer,
                                  from_path, from_buffer,