In zerocopy_fill_skb_from_iter(), if two copy operations are performed and the first one succeeds while the second one fails, it returns a failure but the count in iterator has already been decremented due to the first successful copy. This ultimately affects the local variable rest_len in virtio_transport_send_pkt_info(), causing the remaining count in rest_len to be greater than the actual iterator count. As a result, packet sending operations continue even when the iterator count is zero, which further leads to skb->len being 0 and triggers the warning reported by syzbot [1]. Therefore, if the zerocopy operation fails, we should revert the iterator to its original state. The iov_iter_revert() in skb_zerocopy_iter_stream() is no longer needed and has been removed. Regarding the judgment condition, I aligned it with the condition in skb_zerocopy_iter_stream(). [1] 'send_pkt()' returns 0, but 4096 expected WARNING: net/vmw_vsock/virtio_transport_common.c:430 at virtio_transport_send_pkt_info+0xd1e/0xef0 net/vmw_vsock/virtio_transport_common.c:428, CPU#1: syz.0.17/5986 Call Trace: virtio_transport_stream_enqueue net/vmw_vsock/virtio_transport_common.c:1113 [inline] virtio_transport_seqpacket_enqueue+0x143/0x1c0 net/vmw_vsock/virtio_transport_common.c:841 vsock_connectible_sendmsg+0xabf/0x1040 net/vmw_vsock/af_vsock.c:2158 sock_sendmsg_nosec net/socket.c:727 [inline] __sock_sendmsg+0x21c/0x270 net/socket.c:746 Reported-by: syzbot+28e5f3d207b14bae122a@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=28e5f3d207b14bae122a Signed-off-by: Edward Adam Davis --- v4: - add comments for new condition v3: https://lore.kernel.org/all/tencent_3C86DFD37A0374496263BE24483777D76305@qq.com/ - fix test tcp_zerocopy_maxfrags timeout v2: https://lore.kernel.org/all/tencent_BA768766163C533724966E36344AAE754709@qq.com/ - Remove iov_iter_revert() in skb_zerocopy_iter_stream() v1: https://lore.kernel.org/all/tencent_387517772566B03DBD365896C036264AA809@qq.com/ net/core/datagram.c | 9 ++++++++- net/core/skbuff.c | 1 - 2 files changed, 8 insertions(+), 2 deletions(-) diff --git a/net/core/datagram.c b/net/core/datagram.c index c285c6465923..c5f2f1b8786b 100644 --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -749,8 +749,12 @@ int __zerocopy_sg_from_iter(struct msghdr *msg, struct sock *sk, struct net_devmem_dmabuf_binding *binding) { unsigned long orig_size = skb->truesize; + struct iov_iter_state state; unsigned long truesize; - int ret; + int ret, orig_len; + + iov_iter_save_state(from, &state); + orig_len = skb->len; if (msg && msg->msg_ubuf && msg->sg_from_iter) ret = msg->sg_from_iter(skb, from, length); @@ -759,6 +763,9 @@ int __zerocopy_sg_from_iter(struct msghdr *msg, struct sock *sk, else ret = zerocopy_fill_skb_from_iter(skb, from, length); + if (ret == -EFAULT || (ret == -EMSGSIZE && skb->len == orig_len)) + iov_iter_restore(from, &state); + truesize = skb->truesize - orig_size; if (sk && sk->sk_type == SOCK_STREAM) { sk_wmem_queued_add(sk, truesize); diff --git a/net/core/skbuff.c b/net/core/skbuff.c index a00808f7be6a..7b8836f668b7 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1908,7 +1908,6 @@ int skb_zerocopy_iter_stream(struct sock *sk, struct sk_buff *skb, struct sock *save_sk = skb->sk; /* Streams do not free skb on error. Reset to prev state. */ - iov_iter_revert(&msg->msg_iter, skb->len - orig_len); skb->sk = sk; ___pskb_trim(skb, orig_len); skb->sk = save_sk; -- 2.43.0