[PATCH net] tcp: avoid double destroy in tcp_abort() of an unaccepted child

[Eric Dumazet <edumazet@kernel.org>]

From: Kyle Zeng <kylebot@openai.com>

tcp_abort() checks for TCP_CLOSE while only owning the socket lock,
then grabs the BH lock before calling tcp_done_with_error().

For a child still sitting in a listener accept queue (which can be
reached via SOCK_DESTROY or bpf_sock_destroy()), inet_csk_listen_stop()
can run in this window: it only holds the child BH lock, and calls
inet_child_forget(), which disconnects, orphans and destroys the child.

tcp_abort() then calls tcp_done_with_error() -> tcp_done(), which sees
SOCK_DEAD and calls inet_csk_destroy_sock() a second time, leading to
a double sock_put() and a use-after-free.

Recheck TCP_CLOSE after acquiring the BH lock, unless we just closed
a listener ourselves, in which case tcp_done_with_error() must still
run to report the error.

Note that the WARN_ON(sock_owned_by_user(child)) in
inet_csk_listen_stop() can still trigger in this window.

Fixes: bac76cf89816 ("tcp: fix forever orphan socket caused by tcp_abort")
Signed-off-by: Kyle Zeng <kylebot@openai.com>
[edumazet: recheck TCP_CLOSE under the BH lock instead of moving the test, smaller diff]
Signed-off-by: Eric Dumazet <edumazet@kernel.org>
---
 net/ipv4/tcp.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 1f56d8c0c5fe947072eb5ce50217b13fd33ff74d..6a9566f179e02c3a2e3c91f4ffa96a85190c861d 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -5128,6 +5128,8 @@ void tcp_done(struct sock *sk)
 int tcp_abort(struct sock *sk, int err)
 {
 	int state = inet_sk_state_load(sk);
+	bool listener = false;
+	int ret = 0;
 
 	if (state == TCP_NEW_SYN_RECV) {
 		struct request_sock *req = inet_reqsk(sk);
@@ -5162,21 +5164,31 @@ int tcp_abort(struct sock *sk, int err)
 	if (sk->sk_state == TCP_LISTEN) {
 		tcp_set_state(sk, TCP_CLOSE);
 		inet_csk_listen_stop(sk);
+		listener = true;
 	}
 
 	/* Don't race with BH socket closes such as inet_csk_listen_stop. */
 	local_bh_disable();
 	bh_lock_sock(sk);
 
+	/* An unaccepted child might have been closed by
+	 * inet_csk_listen_stop() while we were not holding its BH lock.
+	 */
+	if (!listener && sk->sk_state == TCP_CLOSE) {
+		ret = -ENOENT;
+		goto out;
+	}
+
 	if (tcp_need_reset(sk->sk_state))
 		tcp_send_active_reset(sk, SK_RST_REASON_TCP_STATE);
 	tcp_done_with_error(sk, err);
 
+out:
 	bh_unlock_sock(sk);
 	local_bh_enable();
 	if (!has_current_bpf_ctx())
 		release_sock(sk);
-	return 0;
+	return ret;
 }
 EXPORT_SYMBOL_GPL(tcp_abort);
 
-- 
2.53.0