Commit 597222f7 authored Aug 30, 2018 by John Fastabend Committed by Daniel Borkmann Sep 02, 2018

bpf: avoid misuse of psock when TCP_ULP_BPF collides with another ULP



Currently we check sk_user_data is non NULL to determine if the sk
exists in a map. However, this is not sufficient to ensure the psock
or the ULP ops are not in use by another user, such as kcm or TLS. To
avoid this when adding a sock to a map also verify it is of the
correct ULP type. Additionally, when releasing a psock verify that
it is the TCP_ULP_BPF type before releasing the ULP. The error case
where we abort an update due to ULP collision can cause this error
path.

For example,

  __sock_map_ctx_update_elem()
     [...]
     err = tcp_set_ulp_id(sock, TCP_ULP_BPF) <- collides with TLS
     if (err)                                <- so err out here
        goto out_free
     [...]
  out_free:
     smap_release_sock() <- calling tcp_cleanup_ulp releases the
                            TLS ULP incorrectly.

Fixes: 2f857d04 ("bpf: sockmap, remove STRPARSER map_flags and add multi-map support")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

parent 97911e0c

kernel/bpf/sockmap.c

+11 −1

Original line number	Diff line number	Diff line
		@@ -1462,9 +1462,15 @@ static void smap_destroy_psock(struct rcu_head *rcu)
		schedule_work(&psock->gc_work);
		}

		static bool psock_is_smap_sk(struct sock *sk)
		{
		return inet_csk(sk)->icsk_ulp_ops == &bpf_tcp_ulp_ops;
		}

		static void smap_release_sock(struct smap_psock psock, struct sock sock)
		{
		if (refcount_dec_and_test(&psock->refcnt)) {
		if (psock_is_smap_sk(sock))
		tcp_cleanup_ulp(sock);
		write_lock_bh(&sock->sk_callback_lock);
		smap_stop_sock(psock, sock);
		@@ -1892,6 +1898,10 @@ static int __sock_map_ctx_update_elem(struct bpf_map *map,
		* doesn't update user data.
		*/
		if (psock) {
		if (!psock_is_smap_sk(sock)) {
		err = -EBUSY;
		goto out_progs;
		}
		if (READ_ONCE(psock->bpf_parse) && parse) {
		err = -EBUSY;
		goto out_progs;