apparmor: Fix wrong dentry in RENAME_EXCHANGE uid check

In apparmor_path_rename(), when handling RENAME_EXCHANGE, the
cond_exchange structure is supposed to carry the attributes of the
*new* dentry (since it is used to authorize moving new_dentry to the
old location). However, line 412 reads:

    vfsuid = i_uid_into_vfsuid(idmap, d_backing_inode(old_dentry));

This fetches the uid of old_dentry instead of new_dentry. As a result,
the RENAME_EXCHANGE permission check uses the wrong file owner, which
can allow a rename that should be denied (if old_dentry's owner has
more privileges) or deny one that should be allowed.

Note that cond_exchange.mode on the line above correctly uses
new_dentry. Only the uid lookup is wrong.

Fix by changing old_dentry to new_dentry in the i_uid_into_vfsuid call.

Fixes: 5e26a01e56fd ("apparmor: use type safe idmapping helpers")
Reviewed-by: Georgia Garcia <georgia.garcia@canonical.com>
Signed-off-by: Dudu Lu <phx0fer@gmail.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index 49b5e4f329832a137b0967fb3547342a0d0a1a03..467f7ac476aa886cb4ded53cdb41593449bd12f3 100644 (file)
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -410,7 +410,7 @@ static int apparmor_path_rename(const struct path *old_dir, struct dentry *old_d
                        struct path_cond cond_exchange = {
                                .mode = d_backing_inode(new_dentry)->i_mode,
                        };
-                       vfsuid = i_uid_into_vfsuid(idmap, d_backing_inode(old_dentry));
+                       vfsuid = i_uid_into_vfsuid(idmap, d_backing_inode(new_dentry));
                        cond_exchange.uid = vfsuid_into_kuid(vfsuid);
 
                        error = aa_path_perm(OP_RENAME_SRC, current_cred(),