[bpf PATCH v2] bpf: avoid misuse of psock when TCP_ULP_BPF collides with another ULP

[John Fastabend <john.fastabend@gmail.com>]

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: 2f857d04601a ("bpf: sockmap, remove STRPARSER map_flags and add multi-map support")
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
---
 kernel/bpf/sockmap.c |   12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
index ce63e58..488ef96 100644
--- a/kernel/bpf/sockmap.c
+++ b/kernel/bpf/sockmap.c
@@ -1462,10 +1462,16 @@ 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)) {
-		tcp_cleanup_ulp(sock);
+		if (psock_is_smap_sk(sock))
+			tcp_cleanup_ulp(sock);
 		write_lock_bh(&sock->sk_callback_lock);
 		smap_stop_sock(psock, sock);
 		write_unlock_bh(&sock->sk_callback_lock);
@@ -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;