This is a note to let you know that I've just added the patch titled dccp: put dccp_qpolicy_full() and dccp_qpolicy_push() in the same lock to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: dccp-put-dccp_qpolicy_full-and-dccp_qpolicy_push-in-.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 9d682186e7b4f4045e5fbeece08aede453af280a Author: Hangyu Hua <hbh25y@xxxxxxxxx> Date: Fri Jul 29 19:00:27 2022 +0800 dccp: put dccp_qpolicy_full() and dccp_qpolicy_push() in the same lock [ Upstream commit a41b17ff9dacd22f5f118ee53d82da0f3e52d5e3 ] In the case of sk->dccps_qpolicy == DCCPQ_POLICY_PRIO, dccp_qpolicy_full will drop a skb when qpolicy is full. And the lock in dccp_sendmsg is released before sock_alloc_send_skb and then relocked after sock_alloc_send_skb. The following conditions may lead dccp_qpolicy_push to add skb to an already full sk_write_queue: thread1--->lock thread1--->dccp_qpolicy_full: queue is full. drop a skb thread1--->unlock thread2--->lock thread2--->dccp_qpolicy_full: queue is not full. no need to drop. thread2--->unlock thread1--->lock thread1--->dccp_qpolicy_push: add a skb. queue is full. thread1--->unlock thread2--->lock thread2--->dccp_qpolicy_push: add a skb! thread2--->unlock Fix this by moving dccp_qpolicy_full. Fixes: b1308dc015eb ("[DCCP]: Set TX Queue Length Bounds via Sysctl") Signed-off-by: Hangyu Hua <hbh25y@xxxxxxxxx> Link: https://lore.kernel.org/r/20220729110027.40569-1-hbh25y@xxxxxxxxx Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/net/dccp/proto.c b/net/dccp/proto.c index cb61a9d281f6..951cbdf05ffe 100644 --- a/net/dccp/proto.c +++ b/net/dccp/proto.c @@ -765,11 +765,6 @@ int dccp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) lock_sock(sk); - if (dccp_qpolicy_full(sk)) { - rc = -EAGAIN; - goto out_release; - } - timeo = sock_sndtimeo(sk, noblock); /* @@ -788,6 +783,11 @@ int dccp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len) if (skb == NULL) goto out_release; + if (dccp_qpolicy_full(sk)) { + rc = -EAGAIN; + goto out_discard; + } + if (sk->sk_state == DCCP_CLOSED) { rc = -ENOTCONN; goto out_discard;