From: Willem de Bruijn willemb@google.com
The referenced commit drops bad input, but has false positives. Tighten the check to avoid these.
The check detects illegal checksum offload requests, which produce csum_start/csum_off beyond end of packet after segmentation.
But it is based on two incorrect assumptions:
1. virtio_net_hdr_to_skb with VIRTIO_NET_HDR_GSO_TCP[46] implies GSO. True in callers that inject into the tx path, such as tap. But false in callers that inject into rx, like virtio-net. Here, the flags indicate GRO, and CHECKSUM_UNNECESSARY or CHECKSUM_NONE without VIRTIO_NET_HDR_F_NEEDS_CSUM is normal.
2. TSO requires checksum offload, i.e., ip_summed == CHECKSUM_PARTIAL. False, as tcp[46]_gso_segment will fix up csum_start and offset for all other ip_summed by calling __tcp_v4_send_check.
Because of 2, we can limit the scope of the fix to virtio_net_hdr that do try to set these fields, with a bogus value.
Link: https://lore.kernel.org/netdev/20240909094527.GA3048202@port70.net/ Fixes: 89add40066f9 ("net: drop bad gso csum_start and offset in virtio_net_hdr") Signed-off-by: Willem de Bruijn willemb@google.com Acked-by: Jason Wang jasowang@redhat.com Acked-by: Michael S. Tsirkin mst@redhat.com Cc: stable@vger.kernel.org
---
Changes v1->v2: - Fix Cc: - Add Acks from v1 --- include/linux/virtio_net.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h index 6c395a2600e8d..276ca543ef44d 100644 --- a/include/linux/virtio_net.h +++ b/include/linux/virtio_net.h @@ -173,7 +173,8 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb, break; case SKB_GSO_TCPV4: case SKB_GSO_TCPV6: - if (skb->csum_offset != offsetof(struct tcphdr, check)) + if (skb->ip_summed == CHECKSUM_PARTIAL && + skb->csum_offset != offsetof(struct tcphdr, check)) return -EINVAL; break; }
Hello:
This patch was applied to netdev/net.git (main) by Jakub Kicinski kuba@kernel.org:
On Tue, 10 Sep 2024 17:35:35 -0400 you wrote:
From: Willem de Bruijn willemb@google.com
The referenced commit drops bad input, but has false positives. Tighten the check to avoid these.
The check detects illegal checksum offload requests, which produce csum_start/csum_off beyond end of packet after segmentation.
[...]
Here is the summary with links: - [net,v2] net: tighten bad gso csum offset check in virtio_net_hdr https://git.kernel.org/netdev/net/c/6513eb3d3191
You are awesome, thank you!
On Tue, Sep 10, 2024 at 05:35:35PM -0400, Willem de Bruijn wrote:
From: Willem de Bruijn willemb@google.com
The referenced commit drops bad input, but has false positives. Tighten the check to avoid these.
The check detects illegal checksum offload requests, which produce csum_start/csum_off beyond end of packet after segmentation.
But it is based on two incorrect assumptions:
- virtio_net_hdr_to_skb with VIRTIO_NET_HDR_GSO_TCP[46] implies GSO.
True in callers that inject into the tx path, such as tap. But false in callers that inject into rx, like virtio-net. Here, the flags indicate GRO, and CHECKSUM_UNNECESSARY or CHECKSUM_NONE without VIRTIO_NET_HDR_F_NEEDS_CSUM is normal.
- TSO requires checksum offload, i.e., ip_summed == CHECKSUM_PARTIAL.
False, as tcp[46]_gso_segment will fix up csum_start and offset for all other ip_summed by calling __tcp_v4_send_check.
Because of 2, we can limit the scope of the fix to virtio_net_hdr that do try to set these fields, with a bogus value.
I see it is already queued and extremely sorry for not testing and getting back earlier. Good news: it does fix the issue in my setup(same as reported at [1])
So, FWIW,
Tested-by: Sudeep Holla sudeep.holla@arm.com
Sudeep Holla wrote:
On Tue, Sep 10, 2024 at 05:35:35PM -0400, Willem de Bruijn wrote:
From: Willem de Bruijn willemb@google.com
The referenced commit drops bad input, but has false positives. Tighten the check to avoid these.
The check detects illegal checksum offload requests, which produce csum_start/csum_off beyond end of packet after segmentation.
But it is based on two incorrect assumptions:
- virtio_net_hdr_to_skb with VIRTIO_NET_HDR_GSO_TCP[46] implies GSO.
True in callers that inject into the tx path, such as tap. But false in callers that inject into rx, like virtio-net. Here, the flags indicate GRO, and CHECKSUM_UNNECESSARY or CHECKSUM_NONE without VIRTIO_NET_HDR_F_NEEDS_CSUM is normal.
- TSO requires checksum offload, i.e., ip_summed == CHECKSUM_PARTIAL.
False, as tcp[46]_gso_segment will fix up csum_start and offset for all other ip_summed by calling __tcp_v4_send_check.
Because of 2, we can limit the scope of the fix to virtio_net_hdr that do try to set these fields, with a bogus value.
I see it is already queued and extremely sorry for not testing and getting back earlier. Good news: it does fix the issue in my setup(same as reported at [1])
So, FWIW,
Tested-by: Sudeep Holla sudeep.holla@arm.com
That is great to hear. Thanks for reporting your results, Sudeep.
linux-stable-mirror@lists.linaro.org
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Sudeep Holla -
Willem de Bruijn