From nobody Mon Dec 1 22:36:15 2025 Received: from xmbghk7.mail.qq.com (xmbghk7.mail.qq.com [43.163.128.54]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8BB892E03EA; Fri, 28 Nov 2025 08:41:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=43.163.128.54 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764319314; cv=none; b=YQWgQk4MDNrw9+d4n0/UxbQBlEwQzpizudoUfj0WNi5SQ62XtIrkCBHgLcT9sTAOpnvpUXTS1TZu2E6HngJDn4V32I4qqeBermf4exKTm4xBLnOAhVLLp2TMzjEc9A5a2faO4oR8bFce7eXa0y4ugFJMc4pbh6GjChjkeOU1HBA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1764319314; c=relaxed/simple; bh=ObBQE2s6w9HpNtJAwbYSXSwHgGEn8nc872DiGO97wuw=; h=Message-ID:From:To:Cc:Subject:Date:In-Reply-To:References: MIME-Version; b=Tzw7F0RPmmFvtpBXWRtkvBXMWXRHE20gxPmH8GxClYtUyYM90391k43U/REnHnsyfj8P6x5c/ARSCar1kOcCbzYOqgPv1YFICx9x/v/Zc7Kk2wtQS1CX4dX5vogVm32CKbO/kmZWK8UG7uRcTLe92LKo9kd19OV61aZU2/YEaUA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=qq.com; spf=pass smtp.mailfrom=qq.com; dkim=pass (1024-bit key) header.d=qq.com header.i=@qq.com header.b=tFQsu/ZA; arc=none smtp.client-ip=43.163.128.54 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=qq.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=qq.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=qq.com header.i=@qq.com header.b="tFQsu/ZA" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=qq.com; s=s201512; t=1764319301; bh=A8mGR1d0H3r4bTkQhku0Qmh1ZtU7rdJN6hfaTO0TCCM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=tFQsu/ZARHr/IuMfdIIEHFK/rTVNGAGMiKOGGz3rA8PosZRwEpOeC9X6y6m4eAtqE AJBsXfKWQGa/HLHuZ4GEITXk/o0n/zD4gwOAQ5KxnB3PbTbk+s10BhPGNrtWIJrYuT rnosBWufLAopFhJavViqU7NUh9uShCgZ29mjARDY= Received: from lxu-ped-host.. ([111.201.7.117]) by newxmesmtplogicsvrsza53-0.qq.com (NewEsmtp) with SMTP id A660CEAC; Fri, 28 Nov 2025 16:41:38 +0800 X-QQ-mid: xmsmtpt1764319298t8lg5qfwq Message-ID: X-QQ-XMAILINFO: OATpkVjS499uRkp6Iutn8gH3U/2cUmQ2vbZNRc0DRSeKbGa5dtJo5Ioh9IVQjx t64wGLlZUkU+vMD8fMxdF0pACrDiveMTe3zsI10UdlU6h+6OljpXgZzKuWbXuB6EyTn+YkWJiJ4a nezFiCWi2eVIJfWiRh1OYxMgtYC4FU7ql0FoA48AE+pjTMczj7A1BL/U4/BImO7ppUM5wKom+WtX C7TXUtJgDOZ3+Q5lbBwh65Ey8ggUt/WlwCnm3O+q5bJE4EC20SRSIxR3Y2uGh3WBdEFmXb+HIZHL Bvq3dQOHCnLAR6sRB51wx+V2H3Dac6V/ZDkvl/JChQU9Tj4f7JrF/JeZLWyMAd7ytFY/fQ9k6lVM wOTZ5iQKqB8zpBgXpUs7nQ82QPkuqvoWB6gsoCdJKAuKsNg/lwA6t6pmp7oErpgT2YNyRlPZigbj sOMv7LEmhw/YqMKdBfRK3EGDPDqmnBPTxwk0Yueq4d7aCBTQSGU46139JdcD/J3cf+Ogf+KKaylP 3oIEXNyIYvwyvZu71sCDRM9Wuv5KyKF5zC5WVO2a5Eav36HBdpw4a/KCmDlNwvGrHfK9FMJoiFid jpOC/KMHbSHistD3Ikz7/B9TV1oYFJJoE20Rs8IvdHX/XMPe5ph5TkvkQQ2/Z6qclGZ+amo5/okW fdfaxtyIK6TsMur2uA0SLTzoJSAzh4QdvVibQ8p9Ql7ul3jT1wi6MvBaFOlh08vooIEZsgQxH+JZ 0KazWIga4LwbR71i2j2onIqAT2tEyqCxt3u0KKe/CRE6zyAwLWuDAhUk+FiFYdLeqP0lCFOUG51x LHoC39ULfKvsqd27ESsaTYMeElVXf0ttE/LJZx4xW4jhMavBBiZMb+Y/yAP0Fh2yTtDetsRKx2X6 uxXXCK7cmdS9ArHz8h7hEiKeWz0szd9WcAHGBoA4e2LQiojE9S+PYTLsER86q2xKT8Ku3VCJ1pu3 MXH7gbOGuhDYENSVJy5Jd8O+tQnHiBY8fB93ZKBH1GxjAsVGpRe3vlDzHKUY3yIGJRwd2+QQY= X-QQ-XMRINFO: OD9hHCdaPRBwq3WW+NvGbIU= From: Edward Adam Davis To: syzbot+28e5f3d207b14bae122a@syzkaller.appspotmail.com Cc: davem@davemloft.net, edumazet@google.com, eperezma@redhat.com, horms@kernel.org, jasowang@redhat.com, kuba@kernel.org, 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, syzkaller-bugs@googlegroups.com, virtualization@lists.linux.dev, xuanzhuo@linux.alibaba.com Subject: [PATCH Next] net: restore the iterator to its original state when an error occurs Date: Fri, 28 Nov 2025 16:41:38 +0800 X-OQ-MSGID: <20251128084137.112073-2-eadavis@qq.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <6928fe78.a70a0220.d98e3.012a.GAE@google.com> References: <6928fe78.a70a0220.d98e3.012a.GAE@google.com> 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. [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 Tested-by: syzbot+28e5f3d207b14bae122a@syzkaller.appspotmail.com Signed-off-by: Edward Adam Davis --- net/core/datagram.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/net/core/datagram.c b/net/core/datagram.c index c285c6465923..da10465cd8a4 100644 --- a/net/core/datagram.c +++ b/net/core/datagram.c @@ -748,10 +748,13 @@ int __zerocopy_sg_from_iter(struct msghdr *msg, struc= t sock *sk, size_t length, struct net_devmem_dmabuf_binding *binding) { + struct iov_iter_state state; unsigned long orig_size =3D skb->truesize; unsigned long truesize; int ret; =20 + iov_iter_save_state(from, &state); + if (msg && msg->msg_ubuf && msg->sg_from_iter) ret =3D msg->sg_from_iter(skb, from, length); else if (binding) @@ -759,6 +762,9 @@ 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) + 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); --=20 2.43.0