This is a note to let you know that I've just added the patch titled kcm: close race conditions on sk_receive_queue to the 4.14-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: kcm-close-race-conditions-on-sk_receive_queue.patch and it can be found in the queue-4.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 5121197ecc5db58c07da95eb1ff82b98b121a221 Mon Sep 17 00:00:00 2001 From: Cong Wang <cong.wang@xxxxxxxxxxxxx> Date: Sun, 13 Nov 2022 16:51:19 -0800 Subject: kcm: close race conditions on sk_receive_queue From: Cong Wang <cong.wang@xxxxxxxxxxxxx> commit 5121197ecc5db58c07da95eb1ff82b98b121a221 upstream. sk->sk_receive_queue is protected by skb queue lock, but for KCM sockets its RX path takes mux->rx_lock to protect more than just skb queue. However, kcm_recvmsg() still only grabs the skb queue lock, so race conditions still exist. We can teach kcm_recvmsg() to grab mux->rx_lock too but this would introduce a potential performance regression as struct kcm_mux can be shared by multiple KCM sockets. So we have to enforce skb queue lock in requeue_rx_msgs() and handle skb peek case carefully in kcm_wait_data(). Fortunately, skb_recv_datagram() already handles it nicely and is widely used by other sockets, we can just switch to skb_recv_datagram() after getting rid of the unnecessary sock lock in kcm_recvmsg() and kcm_splice_read(). Side note: SOCK_DONE is not used by KCM sockets, so it is safe to get rid of this check too. I ran the original syzbot reproducer for 30 min without seeing any issue. Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module") Reported-by: syzbot+278279efdd2730dd14bf@xxxxxxxxxxxxxxxxxxxxxxxxx Reported-by: shaozhengchao <shaozhengchao@xxxxxxxxxx> Cc: Paolo Abeni <pabeni@xxxxxxxxxx> Cc: Tom Herbert <tom@xxxxxxxxxxxxxxx> Signed-off-by: Cong Wang <cong.wang@xxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20221114005119.597905-1-xiyou.wangcong@xxxxxxxxx Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- net/kcm/kcmsock.c | 60 +++++++----------------------------------------------- 1 file changed, 8 insertions(+), 52 deletions(-) --- a/net/kcm/kcmsock.c +++ b/net/kcm/kcmsock.c @@ -224,7 +224,7 @@ static void requeue_rx_msgs(struct kcm_m struct sk_buff *skb; struct kcm_sock *kcm; - while ((skb = __skb_dequeue(head))) { + while ((skb = skb_dequeue(head))) { /* Reset destructor to avoid calling kcm_rcv_ready */ skb->destructor = sock_rfree; skb_orphan(skb); @@ -1085,53 +1085,18 @@ out_error: return err; } -static struct sk_buff *kcm_wait_data(struct sock *sk, int flags, - long timeo, int *err) -{ - struct sk_buff *skb; - - while (!(skb = skb_peek(&sk->sk_receive_queue))) { - if (sk->sk_err) { - *err = sock_error(sk); - return NULL; - } - - if (sock_flag(sk, SOCK_DONE)) - return NULL; - - if ((flags & MSG_DONTWAIT) || !timeo) { - *err = -EAGAIN; - return NULL; - } - - sk_wait_data(sk, &timeo, NULL); - - /* Handle signals */ - if (signal_pending(current)) { - *err = sock_intr_errno(timeo); - return NULL; - } - } - - return skb; -} - static int kcm_recvmsg(struct socket *sock, struct msghdr *msg, size_t len, int flags) { + int noblock = flags & MSG_DONTWAIT; struct sock *sk = sock->sk; struct kcm_sock *kcm = kcm_sk(sk); int err = 0; - long timeo; struct strp_msg *stm; int copied = 0; struct sk_buff *skb; - timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT); - - lock_sock(sk); - - skb = kcm_wait_data(sk, flags, timeo, &err); + skb = skb_recv_datagram(sk, flags, noblock, &err); if (!skb) goto out; @@ -1162,14 +1127,11 @@ msg_finished: /* Finished with message */ msg->msg_flags |= MSG_EOR; KCM_STATS_INCR(kcm->stats.rx_msgs); - skb_unlink(skb, &sk->sk_receive_queue); - kfree_skb(skb); } } out: - release_sock(sk); - + skb_free_datagram(sk, skb); return copied ? : err; } @@ -1177,9 +1139,9 @@ static ssize_t kcm_splice_read(struct so struct pipe_inode_info *pipe, size_t len, unsigned int flags) { + int noblock = flags & MSG_DONTWAIT; struct sock *sk = sock->sk; struct kcm_sock *kcm = kcm_sk(sk); - long timeo; struct strp_msg *stm; int err = 0; ssize_t copied; @@ -1187,11 +1149,7 @@ static ssize_t kcm_splice_read(struct so /* Only support splice for SOCKSEQPACKET */ - timeo = sock_rcvtimeo(sk, flags & MSG_DONTWAIT); - - lock_sock(sk); - - skb = kcm_wait_data(sk, flags, timeo, &err); + skb = skb_recv_datagram(sk, flags, noblock, &err); if (!skb) goto err_out; @@ -1219,13 +1177,11 @@ static ssize_t kcm_splice_read(struct so * finish reading the message. */ - release_sock(sk); - + skb_free_datagram(sk, skb); return copied; err_out: - release_sock(sk); - + skb_free_datagram(sk, skb); return err; } Patches currently in stable-queue which might be from cong.wang@xxxxxxxxxxxxx are queue-4.14/kcm-close-race-conditions-on-sk_receive_queue.patch