af_unix: Annotate data-race of sk->sk_state in unix_inq_len().

[ Upstream commit 3a0f38eb285c8c2eead4b3230c7ac2983707599d ]

ioctl(SIOCINQ) calls unix_inq_len() that checks sk->sk_state first
and returns -EINVAL if it's TCP_LISTEN.

Then, for SOCK_STREAM sockets, unix_inq_len() returns the number of
bytes in recvq.

However, unix_inq_len() does not hold unix_state_lock(), and the
concurrent listen() might change the state after checking sk->sk_state.

If the race occurs, 0 is returned for the listener, instead of -EINVAL,
because the length of skb with embryo is 0.

We could hold unix_state_lock() in unix_inq_len(), but it's overkill
given the result is true for pre-listen() TCP_CLOSE state.

So, let's use READ_ONCE() for sk->sk_state in unix_inq_len().

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index e8bad973285e4e59d48dcdf3f6334f73b870f4b0..8ab1e2a78119540e5997bdfa2deb0c7888be5c9b 100644 (file)
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2579,7 +2579,7 @@ long unix_inq_len(struct sock *sk)
        struct sk_buff *skb;
        long amount = 0;
 
-       if (sk->sk_state == TCP_LISTEN)
+       if (READ_ONCE(sk->sk_state) == TCP_LISTEN)
                return -EINVAL;
 
        spin_lock(&sk->sk_receive_queue.lock);