netdev - [PATCH v1 net 03/15] af_unix: Annotate data-race of sk->sk_state in unix_inq

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Date: Mon, 3 Jun 2024 07:32:19 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>
CC: Kuniyuki Iwashima <kuniyu@...zon.com>, Kuniyuki Iwashima
	<kuni1840@...il.com>, <netdev@...r.kernel.org>
Subject: [PATCH v1 net 03/15] af_unix: Annotate data-race of sk->sk_state in unix_inq_len().

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@...zon.com>
---
 net/unix/af_unix.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 124ca3af1452..dfb74822ed2e 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -3017,7 +3017,7 @@ 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);
-- 
2.30.2