From nobody Sun Feb 8 13:11:03 2026 Received: from m16.mail.163.com (m16.mail.163.com [117.135.210.5]) (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 18B02298CAB; Fri, 6 Feb 2026 05:51:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=117.135.210.5 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770357113; cv=none; b=Hu/2evFYmXnIrysqRE6+ESk3hsRoNQA+gDNAuxTRRIFkaxINKz8JnSFdF9kmcaVcroT2P5L634GsZ1PMmhYnVXSAM/RjrSit8al/NFwPoK9gFGqsTTlOpZ9nLM2phLJgecHGCoKT/HMyHAt43oRi4Fgjrb1u+HR1gQPTg81iFLA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770357113; c=relaxed/simple; bh=RYqdXloqrTVpQ6/Ha38EU1AdCzc9YMGAl4I1Kgwk9IA=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=SFo8677yqM2Z2qO4AYOkdMaaq6iD0bLPBqijdEH1onKsUG1XkRU+TvdTFTdugoG6/FATvP51rK+begL36bEPpobOrsXKu+C/OX/izjnRdfrvPViUx1kn2NFUft4OgMjAzqslpF8kgdY7L+Tmag5PeMp2LE7tii6mBgRJGETC+MI= 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=SM7XOpYD; arc=none smtp.client-ip=117.135.210.5 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="SM7XOpYD" 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=dA 4zof/j+V7ltXHiN5KBnBwB+kE4YImgeqEqw3BtgqM=; b=SM7XOpYDqJIY7aFGlX Y+4jGtIKtC9VsmWFmDN13t2jGP958FmLaP63/EA2Qtr3EU7J+tsuZYPuT5ghRTg6 G6PCzpxnvO2919r3mxHigkTLHgEz2XuexBz11IM8IMQJFsxaiavKDQtQW8CGXAlN g+WqNmDanRw/o1gZ+seD/hlnM= Received: from localhost.localdomain (unknown []) by gzsmtp3 (Coremail) with SMTP id PigvCgDX3KtRgYVp1VXIOA--.82S2; Fri, 06 Feb 2026 13:51:16 +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 v3] bpf: test_run: Fix the null pointer dereference issue in bpf_lwt_xmit_push_encap Date: Fri, 6 Feb 2026 13:51:13 +0800 Message-Id: <20260206055113.63476-1-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: PigvCgDX3KtRgYVp1VXIOA--.82S2 X-Coremail-Antispam: 1Uf129KBjvJXoWxAF4UWFy5ZF1Utr1UWryfZwb_yoWrZFyxpF WUtrW0kF4kJ340qF48Jr4UJ3WYqFWqvF45Wr1Svw1jqF1jqryxXr1SyF4jqrZ8Ar4rur47 J34UtFn7tw1UJaUanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07jYfOwUUUUU= X-CM-SenderInfo: p1dqww5hqjkmqzuzqiywtou0bp/xtbC8hUxqWmFgVXFJQAA3n 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 v3: - use dst_init - Link to v2: https://lore.kernel.org/all/20260205092227.126665-1-yangfeng5= 9949@163.com/ 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..3e1c47d53b82 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -989,6 +989,7 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const = union bpf_attr *kattr, u32 tailroom =3D SKB_DATA_ALIGN(sizeof(struct skb_shared_info)); struct net *net =3D current->nsproxy->net_ns; struct net_device *dev =3D net->loopback_dev; + struct dst_entry bpf_test_run_lwt_xmit_dst; u32 headroom =3D NET_SKB_PAD + NET_IP_ALIGN; u32 linear_sz =3D kattr->test.data_size_in; u32 repeat =3D kattr->test.repeat; @@ -1156,6 +1157,12 @@ 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) { + dst_init(&bpf_test_run_lwt_xmit_dst, NULL, NULL, + DST_OBSOLETE_NONE, DST_NOCOUNT); + bpf_test_run_lwt_xmit_dst.dev =3D dev; + skb_dst_set_noref(skb, &bpf_test_run_lwt_xmit_dst); + } ret =3D bpf_test_run(prog, skb, repeat, &retval, &duration, false); if (ret) goto out; --=20 2.43.0