CVE-2026-23277

In the Linux kernel, the following vulnerability has been resolved:

net/sched: teql: fix NULL pointer dereference in iptunnel_xmit on TEQL slave xmit

teql_master_xmit() calls netdev_start_xmit(skb, slave) to transmit through slave devices, but does not update skb->dev to the slave device beforehand.

When a gretap tunnel is a TEQL slave, the transmit path reaches iptunnel_xmit() which saves dev = skb->dev (still pointing to teql0 master) and later calls iptunnel_xmit_stats(dev, pkt_len). This function does:

get_cpu_ptr(dev->tstats)

Since teql_master_setup() does not set dev->pcpu_stat_type to NETDEV_PCPU_STAT_TSTATS, the core network stack never allocates tstats for teql0, so dev->tstats is NULL. get_cpu_ptr(NULL) computes NULL + __per_cpu_offset[cpu], resulting in a page fault.

BUG: unable to handle page fault for address: ffff8880e6659018 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 68bc067 P4D 68bc067 PUD 0 Oops: Oops: 0002 [#1] SMP KASAN PTI RIP: 0010:iptunnel_xmit (./include/net/ip_tunnels.h:664 net/ipv4/ip_tunnel_core.c:89) Call Trace: ip_tunnel_xmit (net/ipv4/ip_tunnel.c:847) __gre_xmit (net/ipv4/ip_gre.c:478) gre_tap_xmit (net/ipv4/ip_gre.c:779) teql_master_xmit (net/sched/sch_teql.c:319) dev_hard_start_xmit (net/core/dev.c:3887) sch_direct_xmit (net/sched/sch_generic.c:347) __dev_queue_xmit (net/core/dev.c:4802) neigh_direct_output (net/core/neighbour.c:1660) ip_finish_output2 (net/ipv4/ip_output.c:237) __ip_finish_output.part.0 (net/ipv4/ip_output.c:315) ip_mc_output (net/ipv4/ip_output.c:369) ip_send_skb (net/ipv4/ip_output.c:1508) udp_send_skb (net/ipv4/udp.c:1195) udp_sendmsg (net/ipv4/udp.c:1485) inet_sendmsg (net/ipv4/af_inet.c:859) __sys_sendto (net/socket.c:2206)

Fix this by setting skb->dev = slave before calling netdev_start_xmit(), so that tunnel xmit functions see the correct slave device with properly allocated tstats.

Weakness

The product dereferences a pointer that it expects to be valid but is NULL.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/0bad9c86edd22dec4df83c2b29872d66fd8a2ff4
• https://git.kernel.org/stable/c/0cc0c2e661af418bbf7074179ea5cfffc0a5c466
• https://git.kernel.org/stable/c/21ea283c2750c8307aa35ee832b0951cc993c27d
• https://git.kernel.org/stable/c/383493b9940e3d1b5517424081b3e072e20ec43c
• https://git.kernel.org/stable/c/57c153249143333bbf4ecf927bdf8aa2696ee397
• https://git.kernel.org/stable/c/59b06d8b9bdb6b64b3c534c18da68bce5ccd31be
• https://git.kernel.org/stable/c/6b1f563d670162e188a0f2aec39c24b67b106e17
• https://git.kernel.org/stable/c/81a43e8005366f16e629d8c95dfe05beaa8d36a7