From mboxrd@z Thu Jan 1 00:00:00 1970 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 AD6E23290AB; Fri, 27 Feb 2026 08:22:34 +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=1772180559; cv=none; b=Czet4/5iRwUoS3VD4pnmXG9j59EWxG7iWfkSixymRIFJ/ccsa36e9jZ5bhoqLjihSFhkqBhd/2uq6Ox2TawPIo18usDUSNoEmWrllyVnSLukHcTYCgEUOOvZGWqCNMgwODy/4CCtcZTuUncX5E2ZCa/rfrLIGVBZuS8E6oi6ACY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772180559; c=relaxed/simple; bh=HobaWZBtFXByN9gP8NEOawHf34z8YkPHliY4yHEOq30=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=urx5KbFhW1WXOGFbAms1mZKsAOsV912SSo1jPSSjovGJzmytsil3hxMymxpQeEh6wQGONIxSP93RrV957QtgtLcDE5JQgSaDZJDJRPKIfJdbcD/bJFhtBsVmGNnqVXjfNkwWVJyIUHVRAy8nxduS8vgsLsSg+ciUGMfxjrECvyA= 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=XtST389P; 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="XtST389P" 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=bv 0bnnWfTqafl/AhgDRRaz8W+cZTA5rN1wg4PeCIa3M=; b=XtST389P5lEWcycBM4 2/WkqCRkSHxsNgo/ku8d40xg2bO1MGjKha6WLZXkZ0eWh5tFMhAXtvqKqPNFMvl0 X3DwlbaNeQ3bj4FIEiZLktwYEzUzEXBp8ijQANwS6ggSHvQKcpDqKt/ACHAVBqVd zbfk92rH6Vp+3vNRKSoaz/DjY= Received: from localhost.localdomain (unknown []) by gzga-smtp-mtada-g1-0 (Coremail) with SMTP id _____wDXP+oOVKFpNzWPNg--.30755S3; Fri, 27 Feb 2026 16:21:36 +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 v8 bpf-next 1/2] bpf: test_run: Fix the null pointer dereference issue in bpf_lwt_xmit_push_encap Date: Fri, 27 Feb 2026 16:21:32 +0800 Message-Id: <20260227082133.96951-2-yangfeng59949@163.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20260227082133.96951-1-yangfeng59949@163.com> References: <20260227082133.96951-1-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:_____wDXP+oOVKFpNzWPNg--.30755S3 X-Coremail-Antispam: 1Uf129KBjvJXoWxAF4UWFy5ZF1Utr1UWryfZwb_yoWrWr1xpF 4UtrWFgrs5t340qF48Jr4UJw15XFWqyFW5Xr1Svw1jqF1jqr17Xr1ftF4jqrZ8Ar45uFW7 J348twn7tr1UJaUanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x0piyrWrUUUUU= X-CM-SenderInfo: p1dqww5hqjkmqzuzqiywtou0bp/xtbC8RHbVGmhVBHNGwAA30 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 Temporarily add the setting of skb->_skb_refdst before bpf_test_run to resolve 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 --- net/bpf/test_run.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c index 178c4738e63b..54dbda2f6329 100644 --- a/net/bpf/test_run.c +++ b/net/bpf/test_run.c @@ -1156,6 +1156,19 @@ int bpf_prog_test_run_skb(struct bpf_prog *prog, const union bpf_attr *kattr, skb->ip_summed = CHECKSUM_COMPLETE; } + if (prog->type == BPF_PROG_TYPE_LWT_XMIT && !skb_dst(skb)) { + if (!ipv6_bpf_stub) { + pr_warn_once("Please test this program with the IPv6 module enabled\n"); + ret = -EOPNOTSUPP; + goto out; + } +#if IS_ENABLED(CONFIG_IPV6) + rcu_read_lock(); + skb_dst_set_noref(skb, &net->ipv6.ip6_null_entry->dst); + rcu_read_unlock(); +#endif + } + ret = bpf_test_run(prog, skb, repeat, &retval, &duration, false); if (ret) goto out; -- 2.43.0