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([111.201.7.117]) by newxmesmtplogicsvrszb51-1.qq.com (NewEsmtp) with SMTP id E479A21A; Thu, 11 Dec 2025 14:57:07 +0800 X-QQ-mid: xmsmtpt1765436227tzkqso0y1 Message-ID: X-QQ-XMAILINFO: NEuWzguPBXIKkFBhIjI0JCppC3ptFbk1lS7fUYCDHnLMDVAZiSQNyi1Khk2LWl CSu8h7sQXRKu5RTicGmT+1fW434/kXK58/SnFBhZNOD5M2ETOHuot9Lw4u4Gi8QTk3eNVGGtHSwu FakhnYZL0OH+EAGwr1YRMvOk6UY1KNDRDDp01cWJN+8N9o14yNHy1z5HrtgnzO0+SbCK6CZu17vg mcd1M0KFDQL3MFyZhq+ojo1Hj3IJXiKuPiwKM+IO3KzdknT6CqElbYWIWhb3tTw5jfvZOkk85HmC a/TMeuhcs44k5eoRXH3guSDd4RIm1SWMihWM0fG1muWvbiBq2oLjEW7UoLXR3affsVry2AKKyktV yGcNO8rcT7y5dBO9jEfWcH/uAB77On6neRGRK45wnz/AF3LyPKfyCCtwfhf5a59hTCJakPyNi9Ve 60DSNfdVM56HC4aweqZfT9H0WnpyI/iZuB8fecumFudoxSG/D/u0CMr2xEDV92kIc8pPWPlTOL40 HVjoL8V0m766fNvDQFWHjlSEXA7ftbikSsEYHcqHzS/2zGXGbEmQakd5khum5DhhtkmnhRdDBKzR BGJwPUJdGcX/FdulraopUZO6m3BV9UP33ABDvdJW1raeCJq/Jpn0/FldsSQFhzbTYk6JRHDLeDns UGTaFlwPll/FZEbj+Zp0ZqRei1JJALNuEApD5dAiE3cNvPI2MzwFK2P83+XbbIt1Nt0KzA7/7HvW qmpVCfnndYbsZtCvON5zxxYZgiMN3h9VY6nSQUwRZumM4mgl5tW6WnWTEvfD4pKAzIH5VqZqcIlj ZJRYlVKLDjZ8pUxqt4cYF7J7PMG+Bt+gPeaxgQ7YiYRPe8CrLNj5+kv58ymu+YHQ+ojaYK9e3g9M w7AEz2GIRRRA/u4+VaZgmeNdzQlxsy8Oc8LkV8r153oiq62svKXo+J817DcT8avAIEQh7+LaUWN6 4iGGKRE4GBwW5oMHwltCH879+YngKVNRKEiZt9543eYdXeO4C3OG4Cr4/NQznqwH6bmXtNkfoJ0/ L3RfYt7DmsNL+7huFmhC9V80Wk8ZWn5D+++grxW80ApCOBsq+MADOaqWLWQkCg9G0ESUKGO6vziE nzFtDL X-QQ-XMRINFO: NS+P29fieYNw95Bth2bWPxk= From: Edward Adam Davis To: kuba@kernel.org Cc: davem@davemloft.net, eadavis@qq.com, edumazet@google.com, eperezma@redhat.com, horms@kernel.org, jasowang@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, mst@redhat.com, netdev@vger.kernel.org, pabeni@redhat.com, sgarzare@redhat.com, stefanha@redhat.com, syzbot+ci3edb9412aeb2e703@syzkaller.appspotmail.com, syzbot@lists.linux.dev, syzbot@syzkaller.appspotmail.com, syzkaller-bugs@googlegroups.com, virtualization@lists.linux.dev, xuanzhuo@linux.alibaba.com Subject: [PATCH net-next v4] net: restore the iterator to its original state when an error occurs Date: Thu, 11 Dec 2025 14:57:08 +0800 X-OQ-MSGID: <20251211065707.41148-2-eadavis@qq.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" 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_se= nd_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:11= 13 [inline] virtio_transport_seqpacket_enqueue+0x143/0x1c0 net/vmw_vsock/virtio_transp= ort_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=3D28e5f3d207b14bae122a Signed-off-by: Edward Adam Davis --- v4: - add comments for new condition v3: https://lore.kernel.org/all/tencent_3C86DFD37A0374496263BE24483777D7630= 5@qq.com/ - fix test tcp_zerocopy_maxfrags timeout v2: https://lore.kernel.org/all/tencent_BA768766163C533724966E36344AAE75470= 9@qq.com/ - Remove iov_iter_revert() in skb_zerocopy_iter_stream() v1: https://lore.kernel.org/all/tencent_387517772566B03DBD365896C036264AA80= 9@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 =3D skb->truesize; + struct iov_iter_state state; unsigned long truesize; - int ret; + int ret, orig_len; + + iov_iter_save_state(from, &state); + orig_len =3D skb->len; =20 if (msg && msg->msg_ubuf && msg->sg_from_iter) ret =3D msg->sg_from_iter(skb, from, length); @@ -759,6 +763,9 @@ int __zerocopy_sg_from_iter(struct msghdr *msg, struct = sock *sk, else ret =3D zerocopy_fill_skb_from_iter(skb, from, length); =20 + if (ret =3D=3D -EFAULT || (ret =3D=3D -EMSGSIZE && skb->len =3D=3D orig_l= en)) + iov_iter_restore(from, &state); + truesize =3D skb->truesize - orig_size; if (sk && sk->sk_type =3D=3D 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 =3D skb->sk; =20 /* Streams do not free skb on error. Reset to prev state. */ - iov_iter_revert(&msg->msg_iter, skb->len - orig_len); skb->sk =3D sk; ___pskb_trim(skb, orig_len); skb->sk =3D save_sk; --=20 2.43.0