From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from Chamillionaire.breakpoint.cc (Chamillionaire.breakpoint.cc [91.216.245.30]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8169A395AF2; Fri, 10 Jul 2026 14:37:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.216.245.30 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783694280; cv=none; b=pO2G+t4rxCQXH90SWPoOdDApuolR+rmizI28vMTwLFLNTVTTEfHdiDsqL471DxHUQgIX2kC83h0KYX7fwmeKmPbtd+J7KXG1lx0Bh4QsVzILYi0Q8+99om3ZfJqdtjLZJA97AY74Ya0FAq7w+DhZhlAzLbu8m/F8VmWTdAQuV18= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783694280; c=relaxed/simple; bh=/Ctx3z1mNapdwHFWdi6evZ+I2Pcur1bztsXZU79kmKs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=eV7F20/oWyo/bUMavPdXOkXlAnH8nNGAGFcXeCvr2650oNjcGfo4YqewaJSDcFfrx0IBR2NuAWlvamU/CnGXUob4ikbI/xnKhAl7c8RT6ZlJnsZxqLUXJw3/24+ibHNI71R2IrwnRrvhiHn+ZpFEYQxnC6HNoECvYWDf4ipHyr0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=strlen.de; spf=pass smtp.mailfrom=Chamillionaire.breakpoint.cc; arc=none smtp.client-ip=91.216.245.30 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=strlen.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=Chamillionaire.breakpoint.cc Received: by Chamillionaire.breakpoint.cc (Postfix, from userid 1003) id 94624605B5; Fri, 10 Jul 2026 16:37:55 +0200 (CEST) From: Florian Westphal To: Cc: Paolo Abeni , "David S. Miller" , Eric Dumazet , Jakub Kicinski , , pablo@netfilter.org Subject: [PATCH net 3/9] netfilter: bridge: fix stale prevhdr pointer in br_ip6_fragment() Date: Fri, 10 Jul 2026 16:37:27 +0200 Message-ID: <20260710143733.29741-4-fw@strlen.de> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260710143733.29741-1-fw@strlen.de> References: <20260710143733.29741-1-fw@strlen.de> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Xiang Mei (Microsoft)" 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 Fixes: 764dd163ac92 ("netfilter: nf_conntrack_bridge: add support for IPv6") Cc: stable@vger.kernel.org Reported-by: AutonomousCodeSecurity@microsoft.com Signed-off-by: Xiang Mei (Microsoft) Signed-off-by: Florian Westphal --- net/ipv6/netfilter.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/ipv6/netfilter.c b/net/ipv6/netfilter.c index 6d80f85e55fa..a7025ec87035 100644 --- a/net/ipv6/netfilter.c +++ b/net/ipv6/netfilter.c @@ -120,7 +120,7 @@ int br_ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, ktime_t tstamp = skb->tstamp; struct ip6_frag_state state; u8 *prevhdr, nexthdr = 0; - unsigned int mtu, hlen; + unsigned int mtu, hlen, nexthdr_offset; int hroom, err = 0; __be32 frag_id; @@ -129,6 +129,7 @@ int br_ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, goto blackhole; hlen = err; nexthdr = *prevhdr; + nexthdr_offset = prevhdr - skb_network_header(skb); mtu = skb->dev->mtu; if (frag_max_size > mtu || @@ -147,6 +148,7 @@ int br_ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb, (err = skb_checksum_help(skb))) goto blackhole; + prevhdr = skb_network_header(skb) + nexthdr_offset; hroom = LL_RESERVED_SPACE(skb->dev); if (skb_has_frag_list(skb)) { unsigned int first_len = skb_pagelen(skb); -- 2.54.0