From: "Xiang Mei (Microsoft)" <xmei5@asu.edu>
To: Pablo Neira Ayuso <pablo@netfilter.org>,
Florian Westphal <fw@strlen.de>, Phil Sutter <phil@nwl.cc>,
"David S . Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
Simon Horman <horms@kernel.org>
Cc: netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
AutonomousCodeSecurity@microsoft.com,
tgopinath@linux.microsoft.com, kys@microsoft.com,
"Xiang Mei (Microsoft)" <xmei5@asu.edu>
Subject: [PATCH net] netfilter: bridge: fix stale prevhdr pointer in br_ip6_fragment()
Date: Mon, 6 Jul 2026 23:28:50 +0000 [thread overview]
Message-ID: <20260706232850.3333016-1-xmei5@asu.edu> (raw)
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.
Re-find prevhdr after skb_checksum_help() so it points into the current
head.
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
Fixes: 764dd163ac92 ("netfilter: nf_conntrack_bridge: add support for IPv6")
Reported-by: AutonomousCodeSecurity@microsoft.com
Signed-off-by: Xiang Mei (Microsoft) <xmei5@asu.edu>
---
net/ipv6/netfilter.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/net/ipv6/netfilter.c b/net/ipv6/netfilter.c
index 6d80f85e55fa..547879da9532 100644
--- a/net/ipv6/netfilter.c
+++ b/net/ipv6/netfilter.c
@@ -147,6 +147,10 @@ int br_ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
(err = skb_checksum_help(skb)))
goto blackhole;
+ err = ip6_find_1stfragopt(skb, &prevhdr);
+ if (err < 0)
+ goto blackhole;
+
hroom = LL_RESERVED_SPACE(skb->dev);
if (skb_has_frag_list(skb)) {
unsigned int first_len = skb_pagelen(skb);
--
2.43.0
reply other threads:[~2026-07-06 23:28 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20260706232850.3333016-1-xmei5@asu.edu \
--to=xmei5@asu.edu \
--cc=AutonomousCodeSecurity@microsoft.com \
--cc=coreteam@netfilter.org \
--cc=davem@davemloft.net \
--cc=edumazet@google.com \
--cc=fw@strlen.de \
--cc=horms@kernel.org \
--cc=kuba@kernel.org \
--cc=kys@microsoft.com \
--cc=linux-kernel@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=netfilter-devel@vger.kernel.org \
--cc=pabeni@redhat.com \
--cc=pablo@netfilter.org \
--cc=phil@nwl.cc \
--cc=tgopinath@linux.microsoft.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox