From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-189.mta0.migadu.com (out-189.mta0.migadu.com [91.218.175.189]) (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 9FB99296BCF for ; Mon, 8 Jun 2026 12:59:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.189 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780923547; cv=none; b=muMCfLUN5SK3TiK1Zvu1EH/OL78DAtDuc9wqswEdyfXbtMGm8mwbjPvUKA8eGwWzkA5Uzqus+LZCJSFjGCYtLYemrovjROgk3tuYnDXnz+wREQun0Z742FWNbmMlG01XHZK+rrbXu8ksFI63TQ3cqoqCgSOjNv4eL4x5Cw6vWvM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780923547; c=relaxed/simple; bh=5FNPCPysBtlY1McZBVnBdBHZEzilhetJuuzqH/78qcU=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version:Content-Type; b=Tik9WM5OEHMIHdlsSLrfpSQkwb8a0tnEjDAv4XlxBd5itcPaCW0wMvjPpCMPkcE+WOcrW06E1StnU1/SpAbr9ZfLcOocn6lnrdOoqVO6bjTIjyfPr4Aph7Gp5j10v0n5xzNCsJ+MZ3OykTKiZByuZr+X6EB3wtRZW6yXUCPYOVs= 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=l4zdgaSc; arc=none smtp.client-ip=91.218.175.189 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="l4zdgaSc" 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=1780923541; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=PGHH0jvqAvskxAvzSGW+VDZz2ncp2vRZIRhqBagTjPs=; b=l4zdgaScfewFK6IX3WJMvUOIf8TjtU953zJIglPxHvX6jl26BSwH6fRKDHXOsycLMWuA/1 LIoSeHQC4JbLA/YjiskzXx9HmhqUXHZdvlOZEbTKT2BLoMlbZn+sRY22/+cK6EV+c3/n9Q oZdah3OmhOxPwD4sEyAziDx3ncmvA1E= From: Jiayuan Chen To: bpf@vger.kernel.org Cc: Jiayuan Chen , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Willem de Bruijn , Andrii Nakryiko , Eduard Zingerman , Alexei Starovoitov , Daniel Borkmann , Martin KaFai Lau , Kumar Kartikeya Dwivedi , Song Liu , Yonghong Song , Jiri Olsa , Shuah Khan , Joe Stringer , Kuniyuki Iwashima , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH bpf v8 0/2] bpf: tcp: Fix null-ptr-deref in arbitrary SYN Cookie Date: Mon, 8 Jun 2026 20:58:26 +0800 Message-ID: <20260608125846.157004-1-jiayuan.chen@linux.dev> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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 Validating the protocol in the helper is not enough: a BPF program can bypass an ip_hdr(skb)->protocol check via TOCTOU by rewriting the header around the call, and bpf_sk_assign() has the same problem since it can assign any socket type to any skb. So validate the protocol where the assigned socket is consumed instead. Patch 1: Validate the L4 protocol in skb_steal_sock(). Each caller passes the protocol it handles (TCP or UDP), and a prefetched socket whose protocol does not match is rejected, regardless of how it was assigned. Patch 2: Add a selftest that calls bpf_sk_assign_tcp_reqsk() on a UDP skb and verifies the stack no longer crashes. --- 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/ v5: https://lore.kernel.org/bpf/20260401110511.73355-1-jiayuan.chen@linux.dev/ v6: https://lore.kernel.org/all/20260403015851.148209-1-jiayuan.chen@linux.dev/ Changes in v6 & v7: - resend and keep selftest. Changes in v5: - use skb_header_pointer instead of pskb_may_pull. 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): net: Validate protocol in skb_steal_sock() for BPF-assigned sockets selftests/bpf: Add protocol check test for bpf_sk_assign_tcp_reqsk() include/net/inet6_hashtables.h | 7 +- include/net/inet_hashtables.h | 7 +- include/net/request_sock.h | 16 ++- net/ipv4/udp.c | 2 +- net/ipv6/udp.c | 2 +- .../bpf/prog_tests/tcp_custom_syncookie.c | 87 ++++++++++++++- .../bpf/progs/test_tcp_custom_syncookie.c | 102 ++++++++++++++++++ 7 files changed, 210 insertions(+), 13 deletions(-) -- 2.43.0