apparmor: fix NULL sock in aa_sock_file_perm

Deal with the potential that sock and sock-sk can be NULL during
socket setup or teardown. This could lead to an oops. The fix for NULL
pointer dereference in __unix_needs_revalidation shows this is at
least possible for af_unix sockets. While the fix for af_unix sockets
applies for newer mediation this is still the fall back path for older
af_unix mediation and other sockets, so ensure it is covered.

Fixes: 56974a6 ("apparmor: add base infastructure for socket mediation")
Reviewed-by: Georgia Garcia <[email protected]>
Signed-off-by: John Johansen <[email protected]>

Author: jrjohansen

security/apparmor/net.c

@@ -326,8 +326,10 @@ int aa_sock_file_perm(const struct cred *subj_cred, struct aa_label *label,
 	struct socket *sock = (struct socket *) file->private_data;
 
 	AA_BUG(!label);
-	AA_BUG(!sock);
-	AA_BUG(!sock->sk);
+
+	/* sock && sock->sk can be NULL for sockets being set up or torn down */
+	if (!sock || !sock->sk)
+		return 0;
 
 	if (sock->sk->sk_family == PF_UNIX)
 		return aa_unix_file_perm(subj_cred, label, op, request, file);