On Mon, Sep 9, 2024 at 11:02 AM Willem de Bruijn willemdebruijn.kernel@gmail.com wrote:
Jason Wang wrote:
On Mon, Sep 9, 2024 at 4:44 AM Michael S. Tsirkin mst@redhat.com wrote:
On Sun, Sep 08, 2024 at 04:09:43PM -0400, Willem de Bruijn wrote:
Willem de Bruijn wrote:
Szabolcs Nagy wrote:
The 07/29/2024 16:10, Willem de Bruijn wrote: > From: Willem de Bruijn willemb@google.com > > Tighten csum_start and csum_offset checks in virtio_net_hdr_to_skb > for GSO packets. > > The function already checks that a checksum requested with > VIRTIO_NET_HDR_F_NEEDS_CSUM is in skb linear. But for GSO packets > this might not hold for segs after segmentation. > > Syzkaller demonstrated to reach this warning in skb_checksum_help > > offset = skb_checksum_start_offset(skb); > ret = -EINVAL; > if (WARN_ON_ONCE(offset >= skb_headlen(skb))) > > By injecting a TSO packet: > > WARNING: CPU: 1 PID: 3539 at net/core/dev.c:3284 skb_checksum_help+0x3d0/0x5b0 > ip_do_fragment+0x209/0x1b20 net/ipv4/ip_output.c:774 > ip_finish_output_gso net/ipv4/ip_output.c:279 [inline] > __ip_finish_output+0x2bd/0x4b0 net/ipv4/ip_output.c:301 > iptunnel_xmit+0x50c/0x930 net/ipv4/ip_tunnel_core.c:82 > ip_tunnel_xmit+0x2296/0x2c70 net/ipv4/ip_tunnel.c:813 > __gre_xmit net/ipv4/ip_gre.c:469 [inline] > ipgre_xmit+0x759/0xa60 net/ipv4/ip_gre.c:661 > __netdev_start_xmit include/linux/netdevice.h:4850 [inline] > netdev_start_xmit include/linux/netdevice.h:4864 [inline] > xmit_one net/core/dev.c:3595 [inline] > dev_hard_start_xmit+0x261/0x8c0 net/core/dev.c:3611 > __dev_queue_xmit+0x1b97/0x3c90 net/core/dev.c:4261 > packet_snd net/packet/af_packet.c:3073 [inline] > > The geometry of the bad input packet at tcp_gso_segment: > > [ 52.003050][ T8403] skb len=12202 headroom=244 headlen=12093 tailroom=0 > [ 52.003050][ T8403] mac=(168,24) mac_len=24 net=(192,52) trans=244 > [ 52.003050][ T8403] shinfo(txflags=0 nr_frags=1 gso(size=1552 type=3 segs=0)) > [ 52.003050][ T8403] csum(0x60000c7 start=199 offset=1536 > ip_summed=3 complete_sw=0 valid=0 level=0) > > Mitigate with stricter input validation. > > csum_offset: for GSO packets, deduce the correct value from gso_type. > This is already done for USO. Extend it to TSO. Let UFO be: > udp[46]_ufo_fragment ignores these fields and always computes the > checksum in software. > > csum_start: finding the real offset requires parsing to the transport > header. Do not add a parser, use existing segmentation parsing. Thanks > to SKB_GSO_DODGY, that also catches bad packets that are hw offloaded. > Again test both TSO and USO. Do not test UFO for the above reason, and > do not test UDP tunnel offload. > > GSO packet are almost always CHECKSUM_PARTIAL. USO packets may be > CHECKSUM_NONE since commit 10154dbded6d6 ("udp: Allow GSO transmit > from devices with no checksum offload"), but then still these fields > are initialized correctly in udp4_hwcsum/udp6_hwcsum_outgoing. So no > need to test for ip_summed == CHECKSUM_PARTIAL first. > > This revises an existing fix mentioned in the Fixes tag, which broke > small packets with GSO offload, as detected by kselftests. > > Link: https://syzkaller.appspot.com/bug?extid=e1db31216c789f552871 > Link: https://lore.kernel.org/netdev/20240723223109.2196886-1-kuba@kernel.org > Fixes: e269d79c7d35 ("net: missing check virtio") > Cc: stable@vger.kernel.org > Signed-off-by: Willem de Bruijn willemb@google.com > > --- > > v1->v2 > - skb_transport_header instead of skb->transport_header (edumazet@) > - typo: migitate -> mitigate > ---
this breaks booting from nfs root on an arm64 fvp model for me.
i see two fixup commits
commit 30b03f2a0592eee1267298298eac9dd655f55ab2 Author: Jakub Sitnicki jakub@cloudflare.com AuthorDate: 2024-08-08 11:56:22 +0200 Commit: Jakub Kicinski kuba@kernel.org CommitDate: 2024-08-09 21:58:08 -0700
udp: Fall back to software USO if IPv6 extension headers are presentand
commit b128ed5ab27330deeeaf51ea8bb69f1442a96f7f Author: Felix Fietkau nbd@nbd.name AuthorDate: 2024-08-19 17:06:21 +0200 Commit: Jakub Kicinski kuba@kernel.org CommitDate: 2024-08-21 17:15:05 -0700
udp: fix receiving fraglist GSO packetsbut they don't fix the issue for me, at the boot console i see
... [ 3.686846] Sending DHCP requests ., OK [ 3.687302] IP-Config: Got DHCP answer from 172.20.51.254, my address is 172.20.51.1 [ 3.687423] IP-Config: Complete: [ 3.687482] device=eth0, hwaddr=ea:0d:79:71:af:cd, ipaddr=172.20.51.1, mask=255.255.255.0, gw=172.20.51.254 [ 3.687631] host=172.20.51.1, domain=, nis-domain=(none) [ 3.687719] bootserver=172.20.51.254, rootserver=10.2.80.41, rootpath= [ 3.687771] nameserver0=172.20.51.254, nameserver1=172.20.51.252, nameserver2=172.20.51.251 [ 3.689075] clk: Disabling unused clocks [ 3.689167] PM: genpd: Disabling unused power domains [ 3.689258] ALSA device list: [ 3.689330] No soundcards found. [ 3.716297] VFS: Mounted root (nfs4 filesystem) on device 0:24. [ 3.716843] devtmpfs: mounted [ 3.734352] Freeing unused kernel memory: 10112K [ 3.735178] Run /sbin/init as init process [ 3.743770] eth0: bad gso: type: 1, size: 1440 [ 3.744186] eth0: bad gso: type: 1, size: 1440 ... [ 154.610991] eth0: bad gso: type: 1, size: 1440 [ 185.330941] nfs: server 10.2.80.41 not responding, still trying ...
the "bad gso" message keeps repeating and init is not executed.
if i revert the 3 patches above on 6.11-rc6 then init runs without "bad gso" error.
this affects testing the arm64-gcs patches on top of 6.11-rc3 and 6.11-rc6
not sure if this is an fvp or kernel bug.
Thanks for the report, sorry that you're encountering this breakage.
Makes sense that this commit introduced it
if (virtio_net_hdr_to_skb(skb, &hdr->hdr, virtio_is_little_endian(vi->vdev))) { net_warn_ratelimited("%s: bad gso: type: %u, size: %u\n", dev->name, hdr->hdr.gso_type, hdr->hdr.gso_size); goto frame_err; }Type 1 is VIRTIO_NET_HDR_GSO_TCPV4
Most likely this application is inserting a packet with flag VIRTIO_NET_HDR_F_NEEDS_CSUM and a wrong csum_start. Or is requesting TSO without checksum offload at all. In which case the kernel goes out of its way to find the right offset, but may fail.
Which nfs-client is this? I'd like to take a look at the sourcecode.
Unfortunately the kernel warning lacks a few useful pieces of data, such as the other virtio_net_hdr fields and the packet length.
This happens on the virtio-net receive path, so the bad data is received from the hypervisor.
From what I gather that arm64 fvp (Fixed Virtual Platforms) hypervisor
is closed source?
Disabling GRO on this device will likely work as temporary workaround.
What we can do is instead of dropping packets to correct their offset:
case SKB_GSO_TCPV4: case SKB_GSO_TCPV6:
if (skb->csum_offset != offsetof(struct tcphdr, check))return -EINVAL;
if (skb->csum_offset != offsetof(struct tcphdr, check)) {DEBUG_NET_WARN_ON_ONCE(1);skb->csum_offset = offsetof(struct tcphdr, check);}If the issue is in csum_offset. If the new csum_start check fails, that won't help.
It would be helpful to see these values at this point, e.g., with skb_dump(KERN_INFO, skb, false);
It's an iteresting question whether when VIRTIO_NET_F_GUEST_HDRLEN is not negotiated, csum_offset can be relied upon for GRO.
Jason, WDYT?
I don't see how it connects. GUEST_HDRLEN is about transmission but not for receiving, current Linux driver doesn't use hdrlen at all so hardened csum_offset looks like a must.
And we have
""" If one of the VIRTIO_NET_F_GUEST_TSO4, TSO6, UFO, USO4 or USO6 options have been negotiated, the driver MAY use hdr_len only as a hint about the transport header size. The driver MUST NOT rely on hdr_len to be correct. Note: This is due to various bugs in implementations. """
I think I made a mistake in assuming that virtio_net_hdr_to_skb is only used in the tx path, and that the GSO flags thus imply GSO, which requires CHECKSUM_PARTIAL.
In virtnet_receive, this is the rx path and those flags imply GRO. That can use CHECKSUM_UNNECESSARY, as virtnet does:
if (flags & VIRTIO_NET_HDR_F_DATA_VALID) skb->ip_summed = CHECKSUM_UNNECESSARY;So I guess VIRTIO_NET_HDR_GSO_* without VIRTIO_NET_HDR_F_DATA_VALID would be wrong on rx.
But the new check
if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) { [...] case SKB_GSO_TCPV4: case SKB_GSO_TCPV6: if (skb->csum_offset != offsetof(struct tcphdr, check)) return -EINVAL;should be limited to callers of virtio_net_hdr_to_skb on the tx/GSO path.
Looking what the cleanest/minimal patch is to accomplish that.
virtio_net_hdr_to_skb() translates virtio-net header to skb metadata, so it's RX. For TX the helper should be virtio_net_hdr_from_skb() which translates skb metadata to virtio hdr.
Thanks