CVE-2026-64554netfilter: bridge: fix stale prevhdr pointer in br_ip6_fragment()

Official description

In the Linux kernel, the following vulnerability has been resolved: netfilter: bridge: fix stale prevhdr pointer in br_ip6_fragment() br_ip6_fragment() gets prevhdr, a pointer into the skb head, from ip6_find_1stfragopt(), then calls skb_checksum_help(). For a cloned skb skb_checksum_help() reallocates the head via pskb_expand_head(), leaving prevhdr dangling. It is later dereferenced in ip6_frag_next(), causing a use-after-free write. Save prevhdr's offset before skb_checksum_help() and recompute it after, like commit ef0efcd3bd3f ("ipv6: Fix dangling pointer when ipv6 fragment"). BUG: KASAN: slab-use-after-free in ip6_frag_next (net/ipv6/ip6_output.c:857) Write of size 1 at addr ffff888013ff5016 by task exploit/141 Call Trace: ... kasan_report (mm/kasan/report.c:595) ip6_frag_next (net/ipv6/ip6_output.c:857) br_ip6_fragment (net/ipv6/netfilter.c:212) nf_ct_bridge_post (net/bridge/netfilter/nf_conntrack_bridge.c:407) nf_hook_slow (net/netfilter/core.c:619) br_forward_finish (net/bridge/br_forward.c:66) __br_forward (net/bridge/br_forward.c:115) maybe_deliver (net/bridge/br_forward.c:191) br_flood (net/bridge/br_forward.c:245) br_handle_frame_finish (net/bridge/br_input.c:229) br_handle_frame (net/bridge/br_input.c:442) ... packet_sendmsg (net/packet/af_packet.c:3114) ... do_syscall_64 (arch/x86/entry/syscall_64.c:94) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121) Kernel panic - not syncing: Fatal exception in interrupt

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/8c10778ec674b67a07ea042fcba64270f3f38a5a
• https://git.kernel.org/stable/c/2731efa6364e47934c96eb69e01ea131e8af8030
• https://git.kernel.org/stable/c/00c06ef8c018493943891a7d0ca82b71b24f3180
• https://git.kernel.org/stable/c/c141f69d0a0fb16964dbc293650047e69bda8af7
• https://git.kernel.org/stable/c/f2e6596d10783557aeb9668da2a3b4d19deb2001
• https://git.kernel.org/stable/c/1c4f67c89fd27c4df4c70b135c2c59627698b3c0
• https://git.kernel.org/stable/c/4ac981a8b7ce7aec99a52d08f8a8953e8e120067
• https://git.kernel.org/stable/c/86f3ce81dd2b4b0aa2c3016c989a943e4b1b643d