CVE-2026-98401

What the bug is

Syzbot reported a crash in qdisc_pkt_len_segs_init() caused by a stale transport_header offset after tunnel decapsulation. BUG: unable to handle page fault for address: ffffed102091a42e Oops: Oops: 0000 [#1] SMP KASAN NOPTI CPU: 0 UID: 0 PID: 340 Comm: qdisc_uaf_repro Not tainted 7.2.0-rc4-00061-g248951ddc14d #256 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 RIP: 0010:__asan_load2 <IRQ> qdisc_pkt_len_segs_init (net/core/dev.c:4145) __dev_queue_xmit (net/core/dev.c:4787) br_dev_queue_push_xmit (net/bridge/br_forward.c:53) br_handle_frame_finish (net/bridge/br_input.c:229) br_handle_frame (net/bridge/br_input.c:315) __netif_receive_skb_core.constprop.0 (net/core/dev.c:6099) __netif_receive_skb_list_core (net/core/dev.c:6287) netif_receive_skb_list_internal (net/core/dev.c:6445) napi_complete_done (net/core/dev.c:6813) gro_cell_poll (net/core/gro_cells.c:74) __napi_poll (net/core/dev.c:7735) net_rx_action (net/core/dev.c:7798 net/core/dev.c:7955) handle_softirqs (kernel/softirq.c:622) do_softirq (kernel/softirq.c:523 kernel/softirq.c:510 ) __local_bh_enable_ip (kernel/softirq.c:450) tun_get_user (drivers/net/tun.c:1986 (discriminator 1)) tun_chr_write_iter (drivers/net/tun.c:2032) The issue is completely latent until qdisc read transport header in commit 7fb4c1967011 ("net: pull headers in qdisc_pkt_len_segs_init()"). The crash requires four conditions to line up: 1. The incoming packet is encapsulated and carries GSO metadata. The outer transport header offset is stored in skb->transport_header while the packet is still in the outer tunnel context. 2. The tunnel receiver strips the outer headers. skb->data is advanced to the inner frame, but skb->transport_header is left pointing to the now-removed outer L4 header, so it becomes a negative offset relative to the new data. 3. The inner frame is not delivered to the local IP stack. Instead, it is forwarded at L2 by a bridge or HSR, so ip_rcv_core() never runs and the transport header is not reset to the inner L4 offset. 4. The forwarding path calls __dev_queue_xmit(), which enters qdisc_pkt_len_segs_init(). That function computes the GSO header length from skb_transport_offset(skb). Because the offset is negative, the unsigned cast overflows and pskb_may_pull(skb, hdr_len + sizeof(struct tcphdr)) reads past the end of the skb, triggering a KASAN fault or page fault. The issue specifically requires GSO packets (shinfo->gso_size != 0), which are processed/aggregated through gro_cells. Fix this by clearing transport_header to the ~0U sentinel in gro_cell for all tunnnel driver. GTP does not support GRO/GSO, drop the evil GSO packets in GTP directly.

Where it lives

The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.

drivers/net/gtp.c
include/linux/skbuff.h
net/core/gro_cells.c

What this is

GTP (GPRS Tunneling Protocol)MAINTAINERS section matched on drivers/net/gtp.c · osmocom-net-gprs@lists.osmocom.org · Maintained

Kernel module

gtp

Check it on the machine

grep -w CONFIG_GTP /boot/config-$(uname -r)

Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.

lsmod | grep -w gtp

Prints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.

Show whether Debian builds this, per release

Debian builds this, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.

• bookworm, trixie, forky, sidMnot built on amd64/cloud-amd64, arm64/cloud-arm64

M

a module where it is built at all; some flavours do not build it

Build switch

CONFIG_GTP

From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages

Signals

Published

2026-10-14 (4 days ago)source

CVSS

no vector published, unrated

Attack vector

not published

EPSS

0.21%, higher than 10.4% of all CVEssource

CISA KEV

not listedthe KEV catalogue

Debian urgency

not yet assignedsource

Subsystem

drivers/net

Upstream fixes

The versions the CNA records as introducing and fixing this, and the commit for each. source

Introduced	Fixed in	Commit
2.6.12	6.12.111	8c3d4dfcecf7
2.6.12	6.18.53	e4a5b01e59f7
2.6.12	7.2.7	3340b8565b85
2.6.12	7.3	28a57fb2c5df