net: consume xmit errors of GSO frames

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Summary

CVECVE-2026-43194
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-06 12:16:38 UTC
Updated2026-05-06 13:07:51 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: net: consume xmit errors of GSO frames udpgro_frglist.sh and udpgro_bench.sh are the flakiest tests currently in NIPA. They fail in the same exact way, TCP GRO test stalls occasionally and the test gets killed after 10min. These tests use veth to simulate GRO. They attach a trivial ("return XDP_PASS;") XDP program to the veth to force TSO off and NAPI on. Digging into the failure mode we can see that the connection is completely stuck after a burst of drops. The sender's snd_nxt is at sequence number N [1], but the receiver claims to have received (rcv_nxt) up to N + 3 * MSS [2]. Last piece of the puzzle is that senders rtx queue is not empty (let's say the block in the rtx queue is at sequence number N - 4 * MSS [3]). In this state, sender sends a retransmission from the rtx queue with a single segment, and sequence numbers N-4*MSS:N-3*MSS [3]. Receiver sees it and responds with an ACK all the way up to N + 3 * MSS [2]. But sender will reject this ack as TCP_ACK_UNSENT_DATA because it has no recollection of ever sending data that far out [1]. And we are stuck. The root cause is the mess of the xmit return codes. veth returns an error when it can't xmit a frame. We end up with a loss event like this: ------------------------------------------------- | GSO super frame 1 | GSO super frame 2 | |-----------------------------------------------| | seg | seg | seg | seg | seg | seg | seg | seg | | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | ------------------------------------------------- x ok ok <ok>| ok ok ok <x> \\ snd_nxt "x" means packet lost by veth, and "ok" means it went thru. Since veth has TSO disabled in this test it sees individual segments. Segment 1 is on the retransmit queue and will be resent. So why did the sender not advance snd_nxt even tho it clearly did send up to seg 8? tcp_write_xmit() interprets the return code from the core to mean that data has not been sent at all. Since TCP deals with GSO super frames, not individual segment the crux of the problem is that loss of a single segment can be interpreted as loss of all. TCP only sees the last return code for the last segment of the GSO frame (in <> brackets in the diagram above). Of course for the problem to occur we need a setup or a device without a Qdisc. Otherwise Qdisc layer disconnects the protocol layer from the device errors completely. We have multiple ways to fix this. 1) make veth not return an error when it lost a packet. While this is what I think we did in the past, the issue keeps reappearing and it's annoying to debug. The game of whack a mole is not great. 2) fix the damn return codes We only talk about NETDEV_TX_OK and NETDEV_TX_BUSY in the documentation, so maybe we should make the return code from ndo_start_xmit() a boolean. I like that the most, but perhaps some ancient, not-really-networking protocol would suffer. 3) make TCP ignore the errors It is not entirely clear to me what benefit TCP gets from interpreting the result of ip_queue_xmit()? Specifically once the connection is established and we're pushing data - packet loss is just packet loss? 4) this fix Ignore the rc in the Qdisc-less+GSO case, since it's unreliable. We already always return OK in the TCQ_F_CAN_BYPASS case. In the Qdisc-less case let's be a bit more conservative and only mask the GSO errors. This path is taken by non-IP-"networks" like CAN, MCTP etc, so we could regress some ancient thing. This is the simplest, but also maybe the hackiest fix? Similar fix has been proposed by Eric in the past but never committed because original reporter was working with an OOT driver and wasn't providing feedback (see Link).

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 1f59533f9ca5634e7b8914252e48aee9d9cbe501 ae3f627b45fbc3c776a4e484696f3cad7cbb4eca git Not specified
CNA Linux Linux affected 1f59533f9ca5634e7b8914252e48aee9d9cbe501 0c9de092ef8c50a7ee9612811566f0aa81d8d7b6 git Not specified
CNA Linux Linux affected 1f59533f9ca5634e7b8914252e48aee9d9cbe501 56bd32c0edca34041a5c215887fcf562fae2e2db git Not specified
CNA Linux Linux affected 1f59533f9ca5634e7b8914252e48aee9d9cbe501 9ac6aebef4b4bfc5ed408b0b65645981574bc780 git Not specified
CNA Linux Linux affected 1f59533f9ca5634e7b8914252e48aee9d9cbe501 ea5d7787635e26ec1194ec7eec0e8e5ae3bd10a5 git Not specified
CNA Linux Linux affected 1f59533f9ca5634e7b8914252e48aee9d9cbe501 4cb163e9efcac4cd35c3043e097f25081a5c015c git Not specified
CNA Linux Linux affected 1f59533f9ca5634e7b8914252e48aee9d9cbe501 c86901d22c89a6bf4e2f013e948aaabc60869893 git Not specified
CNA Linux Linux affected 1f59533f9ca5634e7b8914252e48aee9d9cbe501 7aa767d0d3d04e50ae94e770db7db8197f666970 git Not specified
CNA Linux Linux affected 3.18 Not specified
CNA Linux Linux unaffected 3.18 semver Not specified
CNA Linux Linux unaffected 5.10.252 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.202 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.165 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.128 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.75 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.16 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19.6 6.19.* semver Not specified
CNA Linux Linux unaffected 7.0 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/0c9de092ef8c50a7ee9612811566f0aa81d8d7b6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ea5d7787635e26ec1194ec7eec0e8e5ae3bd10a5 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/7aa767d0d3d04e50ae94e770db7db8197f666970 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/9ac6aebef4b4bfc5ed408b0b65645981574bc780 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/4cb163e9efcac4cd35c3043e097f25081a5c015c 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/c86901d22c89a6bf4e2f013e948aaabc60869893 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/56bd32c0edca34041a5c215887fcf562fae2e2db 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/ae3f627b45fbc3c776a4e484696f3cad7cbb4eca 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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