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kcm: close race conditions on sk_receive_queue

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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: ab7ac4eb98 ("kcm: Kernel Connection Multiplexor module")
Reported-by: syzbot+278279efdd2730dd14bf@syzkaller.appspotmail.com
Reported-by: shaozhengchao <shaozhengchao@huawei.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Tom Herbert <tom@herbertland.com>
Signed-off-by: Cong Wang <cong.wang@bytedance.com>
Link: https://lore.kernel.org/r/20221114005119.597905-1-xiyou.wangcong@gmail.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Cong Wang 2022-11-13 16:51:19 -08:00 committed by Paolo Abeni
parent 280c0f7cd0
commit 5121197ecc
1 changed files with 6 additions and 52 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

58
net/kcm/kcmsock.c
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@ -222,7 +222,7 @@ static void requeue_rx_msgs(struct kcm_mux *mux, struct sk_buff_head *head)
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 +1085,17 @@ 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)
{
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, &err);
if (!skb)
goto out;
@ -1162,14 +1126,11 @@ 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;
}
@ -1179,7 +1140,6 @@ static ssize_t kcm_splice_read(struct socket *sock, loff_t *ppos,
{
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 +1147,7 @@ static ssize_t kcm_splice_read(struct socket *sock, loff_t *ppos,
/* 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, &err);
if (!skb)
goto err_out;
@ -1219,13 +1175,11 @@ static ssize_t kcm_splice_read(struct socket *sock, loff_t *ppos,
* 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;
}