* [Patch net v2] kcm: close race conditions on sk_receive_queue
@ 2022-11-03 18:46 Cong Wang
2022-11-08 9:13 ` Paolo Abeni
0 siblings, 1 reply; 3+ messages in thread
From: Cong Wang @ 2022-11-03 18:46 UTC (permalink / raw)
To: netdev
Cc: edumazet, Cong Wang, syzbot+278279efdd2730dd14bf, shaozhengchao,
Paolo Abeni, Tom Herbert
From: Cong Wang <cong.wang@bytedance.com>
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().
I ran the original syzbot reproducer for 30 min without seeing any
issue.
Fixes: ab7ac4eb9832 ("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>
---
net/kcm/kcmsock.c | 58 +++++------------------------------------------
1 file changed, 6 insertions(+), 52 deletions(-)
diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index a5004228111d..890a2423f559 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -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 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
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 @@ static int kcm_recvmsg(struct socket *sock, struct msghdr *msg,
/* 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;
}
--
2.34.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [Patch net v2] kcm: close race conditions on sk_receive_queue
2022-11-03 18:46 [Patch net v2] kcm: close race conditions on sk_receive_queue Cong Wang
@ 2022-11-08 9:13 ` Paolo Abeni
2022-11-13 21:29 ` Cong Wang
0 siblings, 1 reply; 3+ messages in thread
From: Paolo Abeni @ 2022-11-08 9:13 UTC (permalink / raw)
To: Cong Wang, netdev
Cc: edumazet, Cong Wang, syzbot+278279efdd2730dd14bf, shaozhengchao,
Tom Herbert
Hello,
On Thu, 2022-11-03 at 11:46 -0700, Cong Wang wrote:
> @@ -1085,53 +1085,17 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
> 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;
It looks like skb_recv_datagram() ignores the SOCK_DONE flag, so this
change could potentially miss some wait_data end coditions. On the flip
side I don't see any place where the SOCK_DONE flag is set for the kcm
socket, so this should be safe, but could you please document this in
the commit message?
[...]
> @@ -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);
We can reach here with skb == NULL and skb_free_datagram() ->
__kfree_skb() -> skb_release_all() does not deal correctly with NULL
skb, you need to check for skb explicitly here (or rearrange the error
paths in a suitable way).
Thanks!
Paolo
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [Patch net v2] kcm: close race conditions on sk_receive_queue
2022-11-08 9:13 ` Paolo Abeni
@ 2022-11-13 21:29 ` Cong Wang
0 siblings, 0 replies; 3+ messages in thread
From: Cong Wang @ 2022-11-13 21:29 UTC (permalink / raw)
To: Paolo Abeni
Cc: netdev, edumazet, Cong Wang, syzbot+278279efdd2730dd14bf,
shaozhengchao, Tom Herbert
On Tue, Nov 08, 2022 at 10:13:23AM +0100, Paolo Abeni wrote:
> Hello,
> On Thu, 2022-11-03 at 11:46 -0700, Cong Wang wrote:
> > @@ -1085,53 +1085,17 @@ static int kcm_sendmsg(struct socket *sock, struct msghdr *msg, size_t len)
> > 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;
>
> It looks like skb_recv_datagram() ignores the SOCK_DONE flag, so this
> change could potentially miss some wait_data end coditions. On the flip
> side I don't see any place where the SOCK_DONE flag is set for the kcm
> socket, so this should be safe, but could you please document this in
> the commit message?
Good catch. Indeed, this flags seems only used by stream sockets, I will
include this in the commit message.
>
> [...]
>
> > @@ -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);
>
> We can reach here with skb == NULL and skb_free_datagram() ->
> __kfree_skb() -> skb_release_all() does not deal correctly with NULL
> skb, you need to check for skb explicitly here (or rearrange the error
> paths in a suitable way).
>
Are you sure? skb_free_datagram() is just consume_skb() which is guarded
by skb_unref() which takes NULL and returns false.
1195 static inline bool skb_unref(struct sk_buff *skb)
1196 {
1197 if (unlikely(!skb))
1198 return false;
1027 void consume_skb(struct sk_buff *skb)
1028 {
1029 if (!skb_unref(skb))
1030 return;
320 void skb_free_datagram(struct sock *sk, struct sk_buff *skb)
321 {
322 consume_skb(skb);
323 }
Thanks.
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2022-11-13 21:29 UTC | newest]
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2022-11-03 18:46 [Patch net v2] kcm: close race conditions on sk_receive_queue Cong Wang
2022-11-08 9:13 ` Paolo Abeni
2022-11-13 21:29 ` Cong Wang
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