af_unix: Disable MSG_OOB handling for sockets in sockmap/sockhash

AF_UNIX socket tracks the most recent OOB packet (in its receive queue)
with an `oob_skb` pointer. BPF redirecting does not account for that: when
an OOB packet is moved between sockets, `oob_skb` is left outdated. This
results in a single skb that may be accessed from two different sockets.

Take the easy way out: silently drop MSG_OOB data targeting any socket that
is in a sockmap or a sockhash. Note that such silent drop is akin to the
fate of redirected skb's scm_fp_list (SCM_RIGHTS, SCM_CREDENTIALS).

For symmetry, forbid MSG_OOB in unix_bpf_recvmsg().

Fixes: 314001f0bf92 ("af_unix: Add OOB support")
Suggested-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Michal Luczaj <mhal@rbox.co>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Jakub Sitnicki <jakub@cloudflare.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/20240713200218.2140950-2-mhal@rbox.co

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index b0a4c6d08e0a6ab752d3f64d46e9b11af5321888..0be0dcb07f7b6253661e9db48ad3e4c9ca855009 100644 (file)
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2721,10 +2721,49 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sock *sk,
 
 static int unix_stream_read_skb(struct sock *sk, skb_read_actor_t recv_actor)
 {
+       struct unix_sock *u = unix_sk(sk);
+       struct sk_buff *skb;
+       int err;
+
        if (unlikely(READ_ONCE(sk->sk_state) != TCP_ESTABLISHED))
                return -ENOTCONN;
 
-       return unix_read_skb(sk, recv_actor);
+       mutex_lock(&u->iolock);
+       skb = skb_recv_datagram(sk, MSG_DONTWAIT, &err);
+       mutex_unlock(&u->iolock);
+       if (!skb)
+               return err;
+
+#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
+       if (unlikely(skb == READ_ONCE(u->oob_skb))) {
+               bool drop = false;
+
+               unix_state_lock(sk);
+
+               if (sock_flag(sk, SOCK_DEAD)) {
+                       unix_state_unlock(sk);
+                       kfree_skb(skb);
+                       return -ECONNRESET;
+               }
+
+               spin_lock(&sk->sk_receive_queue.lock);
+               if (likely(skb == u->oob_skb)) {
+                       WRITE_ONCE(u->oob_skb, NULL);
+                       drop = true;
+               }
+               spin_unlock(&sk->sk_receive_queue.lock);
+
+               unix_state_unlock(sk);
+
+               if (drop) {
+                       WARN_ON_ONCE(skb_unref(skb));
+                       kfree_skb(skb);
+                       return -EAGAIN;
+               }
+       }
+#endif
+
+       return recv_actor(sk, skb);
 }
 
 static int unix_stream_read_generic(struct unix_stream_read_state *state,

diff --git a/net/unix/unix_bpf.c b/net/unix/unix_bpf.c
index bd84785bf8d6c2435de6e21818087ddab2f02562..bca2d86ba97d8d428d63d912cc109397fc4bb122 100644 (file)
--- a/net/unix/unix_bpf.c
+++ b/net/unix/unix_bpf.c
@@ -54,6 +54,9 @@ static int unix_bpf_recvmsg(struct sock *sk, struct msghdr *msg,
        struct sk_psock *psock;
        int copied;
 
+       if (flags & MSG_OOB)
+               return -EOPNOTSUPP;
+
        if (!len)
                return 0;