Messages in this thread | | | Subject | Re: [PATCH net,stable v2] vhost: fix skb leak in handle_rx() | From | Jason Wang <> | Date | Thu, 30 Nov 2017 10:46:17 +0800 |
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On 2017年11月29日 23:31, Michael S. Tsirkin wrote: > On Wed, Nov 29, 2017 at 09:23:24AM -0500,wexu@redhat.com wrote: >> From: Wei Xu<wexu@redhat.com> >> >> Matthew found a roughly 40% tcp throughput regression with commit >> c67df11f(vhost_net: try batch dequing from skb array) as discussed >> in the following thread: >> https://www.mail-archive.com/netdev@vger.kernel.org/msg187936.html >> >> Eventually we figured out that it was a skb leak in handle_rx() >> when sending packets to the VM. This usually happens when a guest >> can not drain out vq as fast as vhost fills in, afterwards it sets >> off the traffic jam and leaks skb(s) which occurs as no headcount >> to send on the vq from vhost side. >> >> This can be avoided by making sure we have got enough headcount >> before actually consuming a skb from the batched rx array while >> transmitting, which is simply done by moving checking the zero >> headcount a bit ahead. >> >> Also strengthen the small possibility of leak in case of recvmsg() >> fails by freeing the skb. >> >> Signed-off-by: Wei Xu<wexu@redhat.com> >> Reported-by: Matthew Rosato<mjrosato@linux.vnet.ibm.com> >> --- >> drivers/vhost/net.c | 23 +++++++++++++---------- >> 1 file changed, 13 insertions(+), 10 deletions(-) >> >> v2: >> - add Matthew as the reporter, thanks matthew. >> - moving zero headcount check ahead instead of defer consuming skb >> due to jason and mst's comment. >> - add freeing skb in favor of recvmsg() fails. >> >> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c >> index 8d626d7..e302e08 100644 >> --- a/drivers/vhost/net.c >> +++ b/drivers/vhost/net.c >> @@ -778,16 +778,6 @@ static void handle_rx(struct vhost_net *net) >> /* On error, stop handling until the next kick. */ >> if (unlikely(headcount < 0)) >> goto out; >> - if (nvq->rx_array) >> - msg.msg_control = vhost_net_buf_consume(&nvq->rxq); >> - /* On overrun, truncate and discard */ >> - if (unlikely(headcount > UIO_MAXIOV)) { >> - iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1); >> - err = sock->ops->recvmsg(sock, &msg, >> - 1, MSG_DONTWAIT | MSG_TRUNC); >> - pr_debug("Discarded rx packet: len %zd\n", sock_len); >> - continue; >> - } >> /* OK, now we need to know about added descriptors. */ >> if (!headcount) { >> if (unlikely(vhost_enable_notify(&net->dev, vq))) { >> @@ -800,6 +790,18 @@ static void handle_rx(struct vhost_net *net) >> * they refilled. */ >> goto out; >> } >> + if (nvq->rx_array) >> + msg.msg_control = vhost_net_buf_consume(&nvq->rxq); >> + /* On overrun, truncate and discard */ >> + if (unlikely(headcount > UIO_MAXIOV)) { >> + iov_iter_init(&msg.msg_iter, READ, vq->iov, 1, 1); >> + err = sock->ops->recvmsg(sock, &msg, >> + 1, MSG_DONTWAIT | MSG_TRUNC); >> + if (unlikely(err != 1)) > Why 1? How is receiving 1 byte special or even possible? > Also, I wouldn't put an unlikely here. It's all error handling code anyway. > >> + kfree_skb((struct sk_buff *)msg.msg_control); > You do not need a cast here. > Also, is it really safe to refer to msg_control here? > I'd rather keep a copy of the skb pointer and use it than assume > caller did not change it. But also see below. > >> + pr_debug("Discarded rx packet: len %zd\n", sock_len); >> + continue; >> + } >> /* We don't need to be notified again. */ >> iov_iter_init(&msg.msg_iter, READ, vq->iov, in, vhost_len); >> fixup = msg.msg_iter; >> @@ -818,6 +820,7 @@ static void handle_rx(struct vhost_net *net) >> pr_debug("Discarded rx packet: " >> " len %d, expected %zd\n", err, sock_len); >> vhost_discard_vq_desc(vq, headcount); >> + kfree_skb((struct sk_buff *)msg.msg_control); > You do not need a cast here. > > Also, we have > > ret = tun_put_user(tun, tfile, skb, to); > if (unlikely(ret < 0)) > kfree_skb(skb); > else > consume_skb(skb); > > return ret; > > So it looks like recvmsg actually always consumes the skb. > So I was wrong when I said you need to kfree it after > recv msg, and your original patch was good. > > Jason, what do you think? >
tun_recvmsg() has the following check:
static int tun_recvmsg(struct socket *sock, struct msghdr *m, size_t total_len, int flags) { struct tun_file *tfile = container_of(sock, struct tun_file, socket); struct tun_struct *tun = __tun_get(tfile); int ret;
if (!tun) return -EBADFD;
if (flags & ~(MSG_DONTWAIT|MSG_TRUNC|MSG_ERRQUEUE)) { ret = -EINVAL; goto out; }
And tun_do_read() has:
if (!iov_iter_count(to)) return 0;
So I think we need free skb in those cases.
Thanks
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