From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f202.google.com (mail-pf1-f202.google.com [209.85.210.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A9E9E1AAE28 for ; Sat, 13 Jun 2026 00:10:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781309420; cv=none; b=ofrmI7NRJanE18LDUXwG9a4gAcSJJH7mXImTCtwd5BND7zzIbgwoouUtSs5+zGoc9F+SIkGOsoZo8PMMXvnj+sR69itwTaLfTkwLbLcB0OHB+B2aEzeXLkLfFVVDFG5A8rPgZl7oB4o77P/Ue5j3rfA58opcVWUg7ntP2pGEQ4o= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781309420; c=relaxed/simple; bh=AF1IlyJR/U93o1LG6v6CBa5cEBHrm4/rODsO1tN/V3o=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=mWDnsCH6nYHHA2sZPVZB8vjLEdAB0Qh+t0KNVOdExpmntFvgf0grv8eiV8WtNhOWL9wlb7lyovg+sj92apfmu+Tl/afC0aYBIsFP4Ft36zJrD6W9tirY4YtPW88gVqhuQFFAoJ3bmYevEAQObq4kYqDPOVKixDj7diVa0ezVCRY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--tavip.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=SBlqT/eq; arc=none smtp.client-ip=209.85.210.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--tavip.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="SBlqT/eq" Received: by mail-pf1-f202.google.com with SMTP id d2e1a72fcca58-8422a0eee68so1990744b3a.0 for ; Fri, 12 Jun 2026 17:10:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1781309418; x=1781914218; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=IfSZlFh04a3h2HSeDtAPuy7d2efg+siOhibP1darPB8=; b=SBlqT/eqY7qi1cC1BvIeH1130U+QPQqUT/VYwtbMCBRM/UUyNUV3Fg7H1GiOEKiURL nN16+XhQzBvJXbuDjWEshEa94SXT03OUxlkUmchax/65AJfeh1pHBl8iO+JsMSa+rtym IMVUOTHUKYFFtB7tT1uRRtp3/ebhmsA6nrQiHh6kiywsbY8us+OepRgXGnDgCIzaNT3A tikn8RScFg/Icf15/NJE9P66fWfZj5FOClLwD2uhi1W4P3w1SqNjW0aH2IxoCWvL55Jj 9dV6wTTBRrFxiAuyrQ05+OkOi23UK+SKsa1Q/SuPUf0rJnW2DBxUBR/zTkFZkHhVFu+0 CeqA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1781309418; x=1781914218; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=IfSZlFh04a3h2HSeDtAPuy7d2efg+siOhibP1darPB8=; b=mgvdCgeZwH+P2f4McuxFZJ+ZKR8t8fIX+L8lAMRHHTwmvGY+X5CreG+rIDp053b+6h SH8MOGzZQ0pytL9IckqyHacXQWpERff99ztrmTxr1GNexZ+cKJpFQc72Bfk1hnILOV9V HxFib/QZ8vZjsXx1NcvL+sQFnnJUKCtnwQtXyoC3ZiQsCDOO4twSTNBYRaAhdn+eJwAY MQhHLUHsVGRITWPTUtdWY40j0GiAujt61ZIh2KLaXCg8icPLsx0pNItQgt6vzB0FmuAe 5H6nYwIMZoBB5GDyx+Q4lyjvqpnshiUsfGdJGRjb95RDuqs8p8SijvLu1KXP+Fkpn546 2JmQ== X-Gm-Message-State: AOJu0YyAU74oupgQJdewGR+LdiFO3Jc6nvAdNrK30Pjy9wRdS4okK1a4 YHzahtZbULzSS9arwTHiIRVi5pm1Z74iKaF/4zM1VIu/t6216kJS6fCjVsZ6i54cpYXeiaQVDvd cF0GOUBet9msP0n7Rse+4l/rhqT1ZGWgunhDd2qJZcfsh1BRci6BWw902+E96q6a46zwMCDpRKA uf0vDa02a1PAM08WHvTR5vPr51iaKcyTk= X-Received: from pfff14.prod.google.com ([2002:a05:6a00:bd0e:b0:842:3b07:6355]) (user=tavip job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:3d48:b0:842:5c60:513 with SMTP id d2e1a72fcca58-8434ce84647mr5472887b3a.30.1781309417753; Fri, 12 Jun 2026 17:10:17 -0700 (PDT) Date: Sat, 13 Jun 2026 00:09:53 +0000 In-Reply-To: <20260613000953.467473-1-tavip@google.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260613000953.467473-1-tavip@google.com> X-Mailer: git-send-email 2.54.0.1136.gdb2ca164c4-goog Message-ID: <20260613000953.467473-3-tavip@google.com> Subject: [PATCH net v2 2/2] vsock/virtio: restore msg_iter on transmission failure From: Octavian Purdila To: netdev@vger.kernel.org Cc: Alexander Viro , Andrew Morton , Arseniy Krasnov , "David S. Miller" , Eric Dumazet , "=?UTF-8?q?Eugenio=20P=C3=A9rez?=" , Jakub Kicinski , Jason Wang , kvm@vger.kernel.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, "Michael S. Tsirkin" , Paolo Abeni , Simon Horman , Stefan Hajnoczi , Stefano Garzarella , virtualization@lists.linux.dev, Xuan Zhuo , Octavian Purdila , syzbot+28e5f3d207b14bae122a@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" When transmission fails in virtio_transport_send_pkt_info, the msg_iter might have been partially advanced. If we don't restore it, the next attempt to send data will use an incorrect iterator state, leading to desync and warnings like "send_pkt() returns 0, but X expected". Specifically, this can happen in the following scenario, triggered by the syzkaller repro: 1. A write-only VMA (PROT_WRITE only) is partially populated by a prior TUN write that failed with -EIO but still faulted in some pages). 2. A vsock sendmmsg call with MSG_ZEROCOPY requests transmission of a buffer from this VMA. 3. The first packet (64KB) is sent successfully because the pages are populated. 4. The second packet allocation fails because GUP fast pins the first page but GUP slow fails on the next unpopulated page due to PROT_WRITE-only permissions. 5. The iterator is advanced by the partially successful GUP (68KB total advanced: 64KB from first packet + 4KB from second), but the send loop breaks and only reports 64KB sent. This creates a 4KB desync. 6. The next retry starts with a non-zero iov_offset, disabling zerocopy and falling back to copy mode. 7. In copy mode, the transmission succeeds for the next packets but exhausts the iterator early because of the desync. 8. The final retry sees an empty iterator but zerocopy is re-enabled (offset resets). It attempts to send the remaining bytes with zerocopy but pins 0 pages, creating an empty packet. 9. The transport sends the empty packet, triggering the warning because the returned bytes (header only) do not match the expected payload size. 10. The loop continues to spin, allocating ubuf_info each time, eventually exhausting sysctl_optmem_max and returning -ENOMEM to userspace. Restore msg_iter to its original state before the packet allocation and transmission attempt if they fail. Fixes: e0718bd82e27 ("vsock: enable setting SO_ZEROCOPY") Reported-by: syzbot+28e5f3d207b14bae122a@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=28e5f3d207b14bae122a Assisted-by: gemini:gemini-3.1-pro Signed-off-by: Octavian Purdila --- net/vmw_vsock/virtio_transport_common.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c index b10666937c490..2baa5a6ebd750 100644 --- a/net/vmw_vsock/virtio_transport_common.c +++ b/net/vmw_vsock/virtio_transport_common.c @@ -295,6 +295,7 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk, u32 max_skb_len = VIRTIO_VSOCK_MAX_PKT_BUF_SIZE; u32 src_cid, src_port, dst_cid, dst_port; const struct virtio_transport *t_ops; + struct iov_iter_state msg_iter_state; struct virtio_vsock_sock *vvs; struct ubuf_info *uarg = NULL; u32 pkt_len = info->pkt_len; @@ -368,8 +369,17 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk, struct sk_buff *skb; size_t skb_len; + /* Save iterator state in case allocation or transmission fails + * so we can restore it and retry. + */ + if (info->msg) + iov_iter_save_state(&info->msg->msg_iter, &msg_iter_state); + skb_len = min(max_skb_len, rest_len); + /* Note: virtio_transport_alloc_skb() can advance info->msg->msg_iter + * even if it fails (e.g. partial GUP success). + */ skb = virtio_transport_alloc_skb(info, skb_len, can_zcopy, uarg, src_cid, src_port, @@ -399,6 +409,9 @@ static int virtio_transport_send_pkt_info(struct vsock_sock *vsk, break; } while (rest_len); + if (info->msg && ret < 0) + iov_iter_restore(&info->msg->msg_iter, &msg_iter_state); + virtio_transport_put_credit(vvs, rest_len); /* msg_zerocopy_realloc() initializes the ubuf_info refcnt to 1. -- 2.54.0.1136.gdb2ca164c4-goog