CVE-2026-23003

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

ip6_tunnel: use skb_vlan_inet_prepare() in __ip6_tnl_rcv()

Blamed commit did not take care of VLAN encapsulations

as spotted by syzbot [1].

Use skb_vlan_inet_prepare() instead of pskb_inet_may_pull().

[1]

BUG: KMSAN: uninit-value in __INET_ECN_decapsulate include/net/inet_ecn.h:253 [inline]

BUG: KMSAN: uninit-value in INET_ECN_decapsulate include/net/inet_ecn.h:275 [inline]

BUG: KMSAN: uninit-value in IP6_ECN_decapsulate+0x7a8/0x1fa0 include/net/inet_ecn.h:321

__INET_ECN_decapsulate include/net/inet_ecn.h:253 [inline]

INET_ECN_decapsulate include/net/inet_ecn.h:275 [inline]

IP6_ECN_decapsulate+0x7a8/0x1fa0 include/net/inet_ecn.h:321

ip6ip6_dscp_ecn_decapsulate+0x16f/0x1b0 net/ipv6/ip6_tunnel.c:729

__ip6_tnl_rcv+0xed9/0x1b50 net/ipv6/ip6_tunnel.c:860

ip6_tnl_rcv+0xc3/0x100 net/ipv6/ip6_tunnel.c:903

gre_rcv+0x1529/0x1b90 net/ipv6/ip6_gre.c:-1

ip6_protocol_deliver_rcu+0x1c89/0x2c60 net/ipv6/ip6_input.c:438

ip6_input_finish+0x1f4/0x4a0 net/ipv6/ip6_input.c:489

NF_HOOK include/linux/netfilter.h:318 [inline]

ip6_input+0x9c/0x330 net/ipv6/ip6_input.c:500

ip6_mc_input+0x7ca/0xc10 net/ipv6/ip6_input.c:590

dst_input include/net/dst.h:474 [inline]

ip6_rcv_finish+0x958/0x990 net/ipv6/ip6_input.c:79

NF_HOOK include/linux/netfilter.h:318 [inline]

ipv6_rcv+0xf1/0x3c0 net/ipv6/ip6_input.c:311

__netif_receive_skb_one_core net/core/dev.c:6139 [inline]

__netif_receive_skb+0x1df/0xac0 net/core/dev.c:6252

netif_receive_skb_internal net/core/dev.c:6338 [inline]

netif_receive_skb+0x57/0x630 net/core/dev.c:6397

tun_rx_batched+0x1df/0x980 drivers/net/tun.c:1485

tun_get_user+0x5c0e/0x6c60 drivers/net/tun.c:1953

tun_chr_write_iter+0x3e9/0x5c0 drivers/net/tun.c:1999

new_sync_write fs/read_write.c:593 [inline]

vfs_write+0xbe2/0x15d0 fs/read_write.c:686

ksys_write fs/read_write.c:738 [inline]

__do_sys_write fs/read_write.c:749 [inline]

__se_sys_write fs/read_write.c:746 [inline]

__x64_sys_write+0x1fb/0x4d0 fs/read_write.c:746

x64_sys_call+0x30ab/0x3e70 arch/x86/include/generated/asm/syscalls_64.h:2

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]

do_syscall_64+0xd3/0xf80 arch/x86/entry/syscall_64.c:94

entry_SYSCALL_64_after_hwframe+0x77/0x7f

Uninit was created at:

slab_post_alloc_hook mm/slub.c:4960 [inline]

slab_alloc_node mm/slub.c:5263 [inline]

kmem_cache_alloc_node_noprof+0x9e7/0x17a0 mm/slub.c:5315

kmalloc_reserve+0x13c/0x4b0 net/core/skbuff.c:586

__alloc_skb+0x805/0x1040 net/core/skbuff.c:690

alloc_skb include/linux/skbuff.h:1383 [inline]

alloc_skb_with_frags+0xc5/0xa60 net/core/skbuff.c:6712

sock_alloc_send_pskb+0xacc/0xc60 net/core/sock.c:2995

tun_alloc_skb drivers/net/tun.c:1461 [inline]

tun_get_user+0x1142/0x6c60 drivers/net/tun.c:1794

tun_chr_write_iter+0x3e9/0x5c0 drivers/net/tun.c:1999

new_sync_write fs/read_write.c:593 [inline]

vfs_write+0xbe2/0x15d0 fs/read_write.c:686

ksys_write fs/read_write.c:738 [inline]

__do_sys_write fs/read_write.c:749 [inline]

__se_sys_write fs/read_write.c:746 [inline]

__x64_sys_write+0x1fb/0x4d0 fs/read_write.c:746

x64_sys_call+0x30ab/0x3e70 arch/x86/include/generated/asm/syscalls_64.h:2

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]

do_syscall_64+0xd3/0xf80 arch/x86/entry/syscall_64.c:94

entry_SYSCALL_64_after_hwframe+0x77/0x7f

CPU: 0 UID: 0 PID: 6465 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(none)

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