CVE-2026-23011

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

ipv4: ip_gre: make ipgre_header() robust

Analog to commit db5b4e39c4e6 ("ip6_gre: make ip6gre_header() robust")

Over the years, syzbot found many ways to crash the kernel

in ipgre_header() [1].

This involves team or bonding drivers ability to dynamically

change their dev->needed_headroom and/or dev->hard_header_len

In this particular crash mld_newpack() allocated an skb

with a too small reserve/headroom, and by the time mld_sendpack()

was called, syzbot managed to attach an ipgre device.

[1]

skbuff: skb_under_panic: text:ffffffff89ea3cb7 len:2030915468 put:2030915372 head:ffff888058b43000 data:ffff887fdfa6e194 tail:0x120 end:0x6c0 dev:team0

kernel BUG at net/core/skbuff.c:213 !

Oops: invalid opcode: 0000 [#1] SMP KASAN PTI

CPU: 1 UID: 0 PID: 1322 Comm: kworker/1:9 Not tainted syzkaller #0 PREEMPT(full)

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025

Workqueue: mld mld_ifc_work

RIP: 0010:skb_panic+0x157/0x160 net/core/skbuff.c:213

Call Trace:

<TASK>

skb_under_panic net/core/skbuff.c:223 [inline]

skb_push+0xc3/0xe0 net/core/skbuff.c:2641

ipgre_header+0x67/0x290 net/ipv4/ip_gre.c:897

dev_hard_header include/linux/netdevice.h:3436 [inline]

neigh_connected_output+0x286/0x460 net/core/neighbour.c:1618

NF_HOOK_COND include/linux/netfilter.h:307 [inline]

ip6_output+0x340/0x550 net/ipv6/ip6_output.c:247

NF_HOOK+0x9e/0x380 include/linux/netfilter.h:318

mld_sendpack+0x8d4/0xe60 net/ipv6/mcast.c:1855

mld_send_cr net/ipv6/mcast.c:2154 [inline]

mld_ifc_work+0x83e/0xd60 net/ipv6/mcast.c:2693

process_one_work kernel/workqueue.c:3257 [inline]

process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340

worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421

kthread+0x711/0x8a0 kernel/kthread.c:463

ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158

ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246