From nobody Tue Feb 10 20:05:57 2026 Received: from m16.mail.163.com (m16.mail.163.com [117.135.210.4]) (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 EF30433EAE7; Tue, 10 Feb 2026 09:07:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=117.135.210.4 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770714478; cv=none; b=Rgb/tQ/iic1eKJqh4W1nNgwdT1yda7WTGX8gZkziwPKWaDGeFXWpsC0JP9MAQsGPhkVzsDnXhW1ABVHdY85pyeG7hzOoM8pE/qcGCb3qPg7APBw6Vbxg6brubX75wX6ZZVrdPdpvWh4WnAtD/GQYp6tKxdC2bktowDlKcehMRUU= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1770714478; c=relaxed/simple; bh=SgcMc8cdRS5boLY4JrT/mh7CqxpfGsmrAlRQqi3yn74=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=A6k0MxsIKCPOvIqsU2VHTSGyqvyA78q+yM0JMWMbrGW8O13/AxLtNxyeZ5gfv5GuOO89JJ4P8w7+D0G3fX9GNkL6EGHLD25EhpYWrYOgL4j8SUrYHPixphtPJ1XBjoT93nFW65SPtHyVd+aZnJj8lZSb1dbSwj/b5u3ttTsphdI= 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=byECU3x6; arc=none smtp.client-ip=117.135.210.4 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="byECU3x6" 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=bh G69paMkB1LYESntXVJ54C7qmLyGAEx1kk1etCRBq8=; b=byECU3x6VRb7B8W9xu OCj2Mj9KCiNrFagAOdNEmw8hO11flwTuisI4FIFWYosIlQuaK/7kvKHbDh2l02Cu T0EDgXfoWl1LshwwrVFD8jrZoHixYQPXs//kOM756JplGCFDYpyS6p6YemOxr47o thIm8Bnx5+mWlDIAS8V8q4tkA= Received: from localhost.localdomain (unknown []) by gzsmtp2 (Coremail) with SMTP id PSgvCgDX7+Yx9YppBLL_Qw--.54996S2; Tue, 10 Feb 2026 17:06:59 +0800 (CST) From: Feng Yang To: davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, yangfeng59949@163.com Subject: [PATCH v5] bpf: test_run: Fix the null pointer dereference issue in bpf_lwt_xmit_push_encap Date: Tue, 10 Feb 2026 17:06:57 +0800 Message-Id: <20260210090657.86977-1-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: PSgvCgDX7+Yx9YppBLL_Qw--.54996S2 X-Coremail-Antispam: 1Uf129KBjvJXoW3WryDWw47Gr4Dtry3Kr4xtFb_yoW7urW7pF 4jyrWFgrs5A34IqF4fJr4xXw1aqFWvyF45Wr1Svw1jvF1jqr17Jr1ftr4jqrs8Ars8ur4x J348tFn7Kw1UXaUanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x0piJ3ktUUUUU= X-CM-SenderInfo: p1dqww5hqjkmqzuzqiywtou0bp/xtbC8hWHAGmK9TXFFwAA3R 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 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 --- Changes in v5: - Refer to the bpf_lwt_xmit_reroute function to configure the dst parameter. - Link to v4: https://lore.kernel.org/all/20260209015111.28144-1-yangfeng59= 949@163.com/ Changes in v4: - add rcu lock - Link to v3: https://lore.kernel.org/all/20260206055113.63476-1-yangfeng59= 949@163.com/ 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 | 47 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 47 insertions(+) diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index 178c4738e63b..dbd2c44da7e5 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -24,6 +24,7 @@ #include #include #include +#include =20 #define CREATE_TRACE_POINTS #include @@ -992,6 +993,7 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const = union bpf_attr *kattr, u32 headroom =3D NET_SKB_PAD + NET_IP_ALIGN; u32 linear_sz =3D kattr->test.data_size_in; u32 repeat =3D kattr->test.repeat; + struct dst_entry *dst =3D NULL; struct __sk_buff *ctx =3D NULL; struct sk_buff *skb =3D NULL; struct sock *sk =3D NULL; @@ -1156,6 +1158,51 @@ 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 && !skb_dst(skb)) { + struct flowi4 fl4 =3D {}; + struct flowi6 fl6 =3D {}; + struct rtable *rt; + + switch (skb->protocol) { + case htons(ETH_P_IP): + if (sizeof(struct iphdr) <=3D skb_headlen(skb)) { + fl4.saddr =3D ip_hdr(skb)->saddr; + fl4.daddr =3D ip_hdr(skb)->daddr; + } + + rt =3D ip_route_output_key(net, &fl4); + if (IS_ERR(rt)) { + ret =3D PTR_ERR(rt); + goto out; + } + dst =3D &rt->dst; + break; +#if IS_ENABLED(CONFIG_IPV6) + case htons(ETH_P_IPV6): + if (sizeof(struct ipv6hdr) <=3D skb_headlen(skb)) { + fl6.saddr =3D ipv6_hdr(skb)->saddr; + fl6.daddr =3D ipv6_hdr(skb)->daddr; + } + + dst =3D ip6_route_output(net, NULL, &fl6); + if (IS_ERR(dst)) { + ret =3D PTR_ERR(dst); + goto out; + } + break; +#endif + default: + ret =3D -EINVAL; + goto out; + } + + if (unlikely(dst->error)) { + ret =3D dst->error; + dst_release(dst); + goto out; + } + skb_dst_set(skb, dst); + } ret =3D bpf_test_run(prog, skb, repeat, &retval, &duration, false); if (ret) goto out; --=20 2.43.0