From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from m16.mail.163.com (m16.mail.163.com [220.197.31.5]) (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 ABE663EBF18; Fri, 13 Feb 2026 02:45:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=220.197.31.5 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770950751; cv=none; b=hOliIDJosTmB87/wxsD/GH+CQ4YJtf/VNYtMwj4dBjxRvB/044iFOG+ibMpNZe1J8JiFGiVCC9hrge6zpQWMiTxJJR+QM1g9/Wq6dSY+Qo5qGjgbwYDioh4liIUTp5v1pjXoYhlNFaoOK4l+1HlVyzFkW2fN4F8eX2kmzgklsNE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770950751; c=relaxed/simple; bh=e9CUNngpJYdidJ+bsQx/7bhJ5yO/Ae4YFVh8fTeAJBA=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=piHILHbJYojSPP2ajoRwMsjJB2/KTGy3PTNdEO93LdJEoea2qTa25EaxidPuN7yPU3NdKihMTGBm4HCmyo/xmgNeJgWTH8hBStyHRdZHnDOgzByQxanJOcdA1npf6ugrfo4LT5XMm+lcnp+rBrL+0+hUgh65wxG9pnXUAOloqlY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=163.com; spf=pass smtp.mailfrom=163.com; dkim=pass (1024-bit key) header.d=163.com header.i=@163.com header.b=Xo7RwQAw; arc=none smtp.client-ip=220.197.31.5 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=163.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=163.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=163.com header.i=@163.com header.b="Xo7RwQAw" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=163.com; s=s110527; h=From:To:Subject:Date:Message-Id:MIME-Version; bh=Ji z9hFkNYU1o3sH3lwWGbmOq3te50YRBL5Jaej3ysfw=; b=Xo7RwQAw0p5xitdrBh ynOAX/X8m3yjEo1OubHAxE9VEveistgccF8K+hPpdt9L0Pgc0e5zVD2H9EDeqOlH c3Os3zs7Y/+uXHmz2yM7qy2wcnLvQQcghzEQlPSQgLc2Oiapix7G04KCc0844ci0 fK21ijcq5qMVWWSM5LEjfGZqQ= Received: from localhost.localdomain (unknown []) by gzga-smtp-mtada-g1-3 (Coremail) with SMTP id _____wAnZNoNkI5pvhZSLw--.1343S3; Fri, 13 Feb 2026 10:44:31 +0800 (CST) From: Feng Yang To: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, posk@google.com, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, yangfeng59949@163.com Subject: [PATCH v6 bpf-next 1/2] bpf: Fix the null pointer dereference issue in bpf_lwt_xmit_push_encap Date: Fri, 13 Feb 2026 10:44:28 +0800 Message-Id: <20260213024429.39972-2-yangfeng59949@163.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20260213024429.39972-1-yangfeng59949@163.com> References: <20260213024429.39972-1-yangfeng59949@163.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CM-TRANSID:_____wAnZNoNkI5pvhZSLw--.1343S3 X-Coremail-Antispam: 1Uf129KBjvJXoWxAF4UWFy5ZF1Utr1UWryfZwb_yoWrGF1Dpr 1jyrW09r4kAry0yF48Jr4UJw129FZ2yFW5Xr1Svw1UXF1Utrn7Xr1SyF4jqrZ8Ar45CrW7 t348t3Z7tr1UJaUanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x0piyrWrUUUUU= X-CM-SenderInfo: p1dqww5hqjkmqzuzqiywtou0bp/xtbC0BAmnmmOkBAyNwAA3a From: Feng Yang The bpf_lwt_xmit_push_encap helper needs to access skb_dst(skb)->dev to calculate the needed headroom: err = skb_cow_head(skb, len + LL_RESERVED_SPACE(skb_dst(skb)->dev)); But skb->_skb_refdst may not be initialized when the skb is set up by bpf_prog_test_run_skb function. Executing bpf_lwt_push_ip_encap function in this scenario will trigger null pointer dereference, causing a kernel crash as Yinhao reported: [ 105.186365] BUG: kernel NULL pointer dereference, address: 0000000000000000 [ 105.186382] #PF: supervisor read access in kernel mode [ 105.186388] #PF: error_code(0x0000) - not-present page [ 105.186393] PGD 121d3d067 P4D 121d3d067 PUD 106c83067 PMD 0 [ 105.186404] Oops: 0000 [#1] PREEMPT SMP NOPTI [ 105.186412] CPU: 3 PID: 3250 Comm: poc Kdump: loaded Not tainted 6.19.0-rc5 #1 [ 105.186423] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 [ 105.186427] RIP: 0010:bpf_lwt_push_ip_encap+0x1eb/0x520 [ 105.186443] Code: 0f 84 de 01 00 00 0f b7 4a 04 66 85 c9 0f 85 47 01 00 00 31 c0 5b 5d 41 5c 41 5d 41 5e c3 cc cc cc cc 48 8b 73 58 48 83 e6 fe <48> 8b 36 0f b7 be ec 00 00 00 0f b7 b6 e6 00 00 00 01 fe 83 e6 f0 [ 105.186449] RSP: 0018:ffffbb0e0387bc50 EFLAGS: 00010246 [ 105.186455] RAX: 000000000000004e RBX: ffff94c74e036500 RCX: ffff94c74874da00 [ 105.186460] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff94c74e036500 [ 105.186463] RBP: 0000000000000001 R08: 0000000000000002 R09: 0000000000000000 [ 105.186467] R10: ffffbb0e0387bd50 R11: 0000000000000000 R12: ffffbb0e0387bc98 [ 105.186471] R13: 0000000000000014 R14: 0000000000000000 R15: 0000000000000002 [ 105.186484] FS: 00007f166aa4d680(0000) GS:ffff94c8b7780000(0000) knlGS:0000000000000000 [ 105.186490] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 105.186494] CR2: 0000000000000000 CR3: 000000015eade001 CR4: 0000000000770ee0 [ 105.186499] PKRU: 55555554 [ 105.186502] Call Trace: [ 105.186507] [ 105.186513] bpf_lwt_xmit_push_encap+0x2b/0x40 [ 105.186522] bpf_prog_a75eaad51e517912+0x41/0x49 [ 105.186536] ? kvm_clock_get_cycles+0x18/0x30 [ 105.186547] ? ktime_get+0x3c/0xa0 [ 105.186554] bpf_test_run+0x195/0x320 [ 105.186563] ? bpf_test_run+0x10f/0x320 [ 105.186579] bpf_prog_test_run_skb+0x2f5/0x4f0 [ 105.186590] __sys_bpf+0x69c/0xa40 [ 105.186603] __x64_sys_bpf+0x1e/0x30 [ 105.186611] do_syscall_64+0x59/0x110 [ 105.186620] entry_SYSCALL_64_after_hwframe+0x76/0xe0 [ 105.186649] RIP: 0033:0x7f166a97455d Check the skb->_skb_refdst in bpf_lwt_push_ip_encap function, and return -EINVAL if _skb_refdst is NULL. Fixes: 52f278774e79 ("bpf: implement BPF_LWT_ENCAP_IP mode in bpf_lwt_push_encap") Reported-by: Yinhao Hu Reported-by: Kaiyan Mei Closes: https://groups.google.com/g/hust-os-kernel-patches/c/8-a0kPpBW2s Signed-off-by: Yun Lu Signed-off-by: Feng Yang Tested-by: syzbot@syzkaller.appspotmail.com --- net/core/lwt_bpf.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/net/core/lwt_bpf.c b/net/core/lwt_bpf.c index 9f40be0c3e71..374054e1a2c6 100644 --- a/net/core/lwt_bpf.c +++ b/net/core/lwt_bpf.c @@ -616,11 +616,14 @@ int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len, bool ingress) return -EINVAL; } - if (ingress) + if (ingress) { err = skb_cow_head(skb, len + skb->mac_len); - else + } else { + if (unlikely(!skb_dst(skb))) + return -EINVAL; err = skb_cow_head(skb, len + LL_RESERVED_SPACE(skb_dst(skb)->dev)); + } if (unlikely(err)) return err; -- 2.43.0