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+From 6513eb3d3191574b58859ef2d6dc26c0277c6f81 Mon Sep 17 00:00:00 2001
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+From: Willem de Bruijn <willemb@google.com>
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+Date: Tue, 10 Sep 2024 17:35:35 -0400
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+Subject: [PATCH] net: tighten bad gso csum offset check in virtio_net_hdr
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+
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+The referenced commit drops bad input, but has false positives.
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+Tighten the check to avoid these.
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+
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+The check detects illegal checksum offload requests, which produce
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+csum_start/csum_off beyond end of packet after segmentation.
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+
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+But it is based on two incorrect assumptions:
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+
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+1. virtio_net_hdr_to_skb with VIRTIO_NET_HDR_GSO_TCP[46] implies GSO.
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+True in callers that inject into the tx path, such as tap.
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+But false in callers that inject into rx, like virtio-net.
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+Here, the flags indicate GRO, and CHECKSUM_UNNECESSARY or
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+CHECKSUM_NONE without VIRTIO_NET_HDR_F_NEEDS_CSUM is normal.
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+
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+2. TSO requires checksum offload, i.e., ip_summed == CHECKSUM_PARTIAL.
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+False, as tcp[46]_gso_segment will fix up csum_start and offset for
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+all other ip_summed by calling __tcp_v4_send_check.
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+
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+Because of 2, we can limit the scope of the fix to virtio_net_hdr
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+that do try to set these fields, with a bogus value.
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+
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+Link: https://lore.kernel.org/netdev/20240909094527.GA3048202@port70.net/
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+Fixes: 89add40066f9 ("net: drop bad gso csum_start and offset in virtio_net_hdr")
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+Signed-off-by: Willem de Bruijn <willemb@google.com>
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+Acked-by: Jason Wang <jasowang@redhat.com>
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+Acked-by: Michael S. Tsirkin <mst@redhat.com>
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+Cc: stable@vger.kernel.org
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+Link: https://patch.msgid.link/20240910213553.839926-1-willemdebruijn.kernel@gmail.com
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+Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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+
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+Upstream-Status: Backport
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+Signed-off-by: Jon Mason <jon.mason@arm.com>
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+
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+---
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+ include/linux/virtio_net.h | 3 ++-
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+ 1 file changed, 2 insertions(+), 1 deletion(-)
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+
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+diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
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+index 6c395a2600e8..276ca543ef44 100644
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+--- a/include/linux/virtio_net.h
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++++ b/include/linux/virtio_net.h
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+@@ -173,7 +173,8 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
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+ break;
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+ case SKB_GSO_TCPV4:
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+ case SKB_GSO_TCPV6:
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+- if (skb->csum_offset != offsetof(struct tcphdr, check))
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++ if (skb->ip_summed == CHECKSUM_PARTIAL &&
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++ skb->csum_offset != offsetof(struct tcphdr, check))
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+ return -EINVAL;
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+ break;
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+ }
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+--
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+2.39.2
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+
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