From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-174.mta0.migadu.com (out-174.mta0.migadu.com [91.218.175.174]) (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 3E0EF2F9984 for ; Wed, 1 Apr 2026 11:05:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.174 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775041548; cv=none; b=fBj4tJnL0Yx6GE6QNYzL6CdqIkwAf/qCceeD3zjyYj/2WhghD9CkjajehbUh6cJcSNKoqdTrtBKhDXbCHdQEQ5LsQdrTYY39JYvytkcc0Tx69cX1XBur6Uq3kowDJKrEuUhg7X4Je/bYut4ag42uvw4jntDf5gf0n53M4XwsnOU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775041548; c=relaxed/simple; bh=QX6YcIS8aDtWOlo3nRiP3ADhmeIP9kM1kSmfsZ36zGc=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=DQUD686THmmQPKgB/d6ioUHvvOC9yhCx0dP4bOqTHvCAQSo9pDGH1Lfzg4Lc1E+Pqn2NnRQvOtqAI8qZsaVbKQRMNpE9Wkbe+Hee0rGAlTA1g2eDeKiMWYRIQ/RzRSiXh0pYPy9Cx7JNLPXb1VhzzBn7b2udFrJbWe7KAFqRYUM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=nWUFtDZ0; arc=none smtp.client-ip=91.218.175.174 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="nWUFtDZ0" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1775041533; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=awnZxp/u7WMTZ1nHWIvAJbHaDUNgRFNmp2rxXHzr9ZM=; b=nWUFtDZ0inpwwANY7t9NH3zzcZy082lPqJffG3i4D0YFe9DbO9YIPUMKrg4pW4Z4hEeCZq u5goBt3tcq08TrKgsu9+juK5EM2T62h6eqOPTIG+Cre0y8YQbbVLac3KJRqQuTEbbVs844 uJ7iMq0zmop90zZTldYOXaDLT8lf3fQ= From: Jiayuan Chen To: bpf@vger.kernel.org Cc: Jiayuan Chen , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Eduard Zingerman , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Shuah Khan , Jiayuan Chen , Kuniyuki Iwashima , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH bpf v5 0/2] bpf: tcp: Fix null-ptr-deref in arbitrary SYN Cookie Date: Wed, 1 Apr 2026 19:04:48 +0800 Message-ID: <20260401110511.73355-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT From: Jiayuan Chen bpf_sk_assign_tcp_reqsk() does not validate the L4 protocol of the skb, only checking skb->protocol (L3). A BPF program that calls this kfunc on a non-TCP skb (e.g. UDP) will succeed, attaching a TCP reqsk to the skb. When the skb enters the UDP receive path, skb_steal_sock() returns the TCP listener socket from the reqsk. The UDP code then casts this TCP socket to udp_sock and accesses UDP-specific fields at invalid offsets, causing a null pointer dereference: BUG: KASAN: null-ptr-deref in __udp_enqueue_schedule_skb+0x19d/0x1df0 Read of size 4 at addr 0000000000000008 by task test_progs/537 CPU: 1 UID: 0 PID: 537 Comm: test_progs Not tainted 7.0.0-rc4+ #46 PREEMPT Call Trace: dump_stack_lvl (lib/dump_stack.c:123) print_report (mm/kasan/report.c:487) kasan_report (mm/kasan/report.c:597) __kasan_check_read (mm/kasan/shadow.c:32) __udp_enqueue_schedule_skb (net/ipv4/udp.c:1719) udp_queue_rcv_one_skb (net/ipv4/udp.c:2370 net/ipv4/udp.c:2500) udp_queue_rcv_skb (net/ipv4/udp.c:2532) udp_unicast_rcv_skb (net/ipv4/udp.c:2684) __udp4_lib_rcv (net/ipv4/udp.c:2742) udp_rcv (net/ipv4/udp.c:2937) ip_protocol_deliver_rcu (net/ipv4/ip_input.c:209) ip_local_deliver_finish (./include/linux/rcupdate.h:879 net/ipv4/ip_input.c:242) ip_local_deliver (net/ipv4/ip_input.c:265) __netif_receive_skb_one_core (net/core/dev.c:6164 (discriminator 4)) __netif_receive_skb (net/core/dev.c:6280) Solution Patch 1: Add L4 protocol validation in bpf_sk_assign_tcp_reqsk(). Check ip_hdr(skb)->protocol (IPv4) and ipv6_hdr(skb)->nexthdr (IPv6) against IPPROTO_TCP, returning -EINVAL for non-TCP skbs. Patch 2: Add selftest that calls bpf_sk_assign_tcp_reqsk() on a UDP skb and verifies the kfunc rejects it. --- v1: https://lore.kernel.org/bpf/20260323105510.51990-1-jiayuan.chen@linux.dev/ v2: https://lore.kernel.org/bpf/20260326062657.88446-1-jiayuan.chen@linux.dev/ v3: https://lore.kernel.org/bpf/20260327133915.286037-1-jiayuan.chen@linux.dev/ v4: https://lore.kernel.org/bpf/20260330080746.319680-1-jiayuan.chen@linux.dev/ Changes in v5: - Add pskb_may_pull before accessing IP/IPv6 headers in kfunc - Use buf[] instead of buf[32], verify recv data with ASSERT_STREQ - Remove unnecessary variable initializations in selftest and BPF Changes in v4: - Check if assign_ret is EINVAL instead of checking if it is 0 Changes in v3: - Add IPv6 test coverage, reuse test_cases[] to iterate over both address families - Share TCP/UDP port to simplify BPF program, remove unnecessary global variables - Use connect_to_fd() + send()/recv() instead of manual sockaddr construction - Suggested by Kuniyuki Iwashima Changes in v2: - Add Reviewed-by tag from Kuniyuki Iwashima for patch 1 - Use UDP socket recv() instead of kern_sync_rcu() for synchronization in selftest Jiayuan Chen (2): bpf: tcp: Reject non-TCP skb in bpf_sk_assign_tcp_reqsk() selftests/bpf: Add protocol check test for bpf_sk_assign_tcp_reqsk() net/core/filter.c | 12 ++ .../bpf/prog_tests/tcp_custom_syncookie.c | 93 ++++++++++++++- .../bpf/progs/test_tcp_custom_syncookie.c | 109 ++++++++++++++++++ 3 files changed, 210 insertions(+), 4 deletions(-) -- 2.43.0