From nobody Mon Feb 9 04:44:40 2026 Received: from m16.mail.163.com (m16.mail.163.com [220.197.31.4]) (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 EE558361672; Thu, 5 Feb 2026 09:23:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=220.197.31.4 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770283395; cv=none; b=AtKLqof1+Mqp2m2zubhxdSn6AcC/QLSO6t3JQCLeNeZsErnqI9Nt8pDpj5BXEQIFN3EmwJNNkOkbQ9qSsUXZ+P3egz49/8VxYnHlsgMDU8ZbkkxPPwjRclQr5AzCn3AkgCrCYLI3Da5LOfn2pq6AKFmIH43b9MFakSO47YQlvK0= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770283395; c=relaxed/simple; bh=ASFscKfQZNTqdX/nIkBWTYyfKL3Xxu/c8YcFqW2TIRg=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=GyZGSmwGJkv0Rq/Os2pQFx1KSB+G1NadCy1pJPWw59reNMpF6UxWrTlqPXpVpq4BJeeaZz1aW89JZsBDvUDTTXKxxuIZNZkZ3z7Mx+FFYEOZf60E8MFOyej2CY97EOMZ3delfV1LpL4mSe1qM28lo7KcJQerTpCHwX8BIhg+24k= 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=HYC1fRc4; arc=none smtp.client-ip=220.197.31.4 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="HYC1fRc4" 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=Hb ZLkhI9yayHaUp7I8gdb9rZtco+zUFIDWHACs6Uq6Q=; b=HYC1fRc4lWnpdZjEOB zef9RiVm1ulu9ToGu0CmDfGK0A1H7EXDPvsW25ZAAuhibnGE+dEUUwfi2Ri/XVja mkL3TgK5lDRX55Ayj4AJETRRj4f7IY3o6XSqj7yuhVg7tX3kLeJw1q7P/SD24Axy rwi+WEuyoodzaBTk8ieetrmW8= Received: from localhost.localdomain (unknown []) by gzga-smtp-mtada-g1-3 (Coremail) with SMTP id _____wAX_mlTYYRpN2GXKQ--.9587S2; Thu, 05 Feb 2026 17:22:29 +0800 (CST) From: Feng Yang To: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH v2] bpf: test_run: Fix the null pointer dereference issue in bpf_lwt_xmit_push_encap Date: Thu, 5 Feb 2026 17:22:27 +0800 Message-Id: <20260205092227.126665-1-yangfeng59949@163.com> X-Mailer: git-send-email 2.25.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-CM-TRANSID: _____wAX_mlTYYRpN2GXKQ--.9587S2 X-Coremail-Antispam: 1Uf129KBjvJXoWxAF4UWFy5ZF1Utr1UWryfZwb_yoWrWw4fpF 1UtrW09rs5J340qF48Jr4UJw1aqFWqvFW5Jryavw1jqF1jqw1xXr1ftF4jgrZ8Ar4ruw47 J34UKFn2qw1UJaUanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07jY89tUUUUU= X-CM-SenderInfo: p1dqww5hqjkmqzuzqiywtou0bp/xtbC8RboYWmEYVZuyQAA3T Content-Type: text/plain; charset="utf-8" From: Feng Yang The bpf_lwt_xmit_push_encap helper needs to access skb_dst(skb)->dev to calculate the needed headroom: err =3D 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: 0000000000000= 000 [ 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 1.1= 6.3-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: ffff94c7487= 4da00 [ 105.186460] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff94c74e0= 36500 [ 105.186463] RBP: 0000000000000001 R08: 0000000000000002 R09: 00000000000= 00000 [ 105.186467] R10: ffffbb0e0387bd50 R11: 0000000000000000 R12: ffffbb0e038= 7bc98 [ 105.186471] R13: 0000000000000014 R14: 0000000000000000 R15: 00000000000= 00002 [ 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: 00000000007= 70ee0 [ 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 Temporarily add the setting of skb->_skb_refdst before bpf_test_run to reso= lve the issue. Fixes: 52f278774e79 ("bpf: implement BPF_LWT_ENCAP_IP mode in bpf_lwt_push_= encap") Reported-by: Yinhao Hu Reported-by: Kaiyan Mei Signed-off-by: Yun Lu Signed-off-by: Feng Yang --- Changes in v2: - Link to v1: https://lore.kernel.org/all/20260127084520.13890-1-luyun_611@= 163.com/=20 --- net/bpf/test_run.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index 178c4738e63b..c05b31cd1741 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -982,6 +982,7 @@ static struct proto bpf_dummy_proto =3D { .obj_size =3D sizeof(struct sock), }; =20 +struct dst_entry bpf_test_run_lwt_xmit_dst; int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kat= tr, union bpf_attr __user *uattr) { @@ -1156,7 +1157,13 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, con= st union bpf_attr *kattr, skb->ip_summed =3D CHECKSUM_COMPLETE; } =20 + if (prog->type =3D=3D BPF_PROG_TYPE_LWT_XMIT) { + bpf_test_run_lwt_xmit_dst.dev =3D dev; + skb_dst_set(skb, &bpf_test_run_lwt_xmit_dst); + } ret =3D bpf_test_run(prog, skb, repeat, &retval, &duration, false); + if (prog->type =3D=3D BPF_PROG_TYPE_LWT_XMIT) + skb_dst_set(skb, NULL); if (ret) goto out; if (!is_l2) { --=20 2.43.0