From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-186.mta0.migadu.com (out-186.mta0.migadu.com [91.218.175.186]) (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 26E441D45E8 for ; Mon, 6 Apr 2026 19:53:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.186 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775505199; cv=none; b=gW3GhY8IACeXid2wSI9lLO1Z1wL3YQqHK5mFfDKkRqeQRT/78WimwpMRPSNxLnUwtYKOmkW67LmuO3UgS+NNf8MRyOPcF8FC4Yx3aXaKHJHii3b3JDf8adkoLdZ33CPqC344bGvMVMJI0Yfw1ikeNg3zwhhvI6/vRLK1p5cvFOM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775505199; c=relaxed/simple; bh=eouATSlX8G6NY+XWDHTk7j04brbeOYKRBaUKpumKmWA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=s/0/NozVhha8VKgxjtj9n20I+A+agZvcdKGbEbL7AB3sXGMVSqU8AYaIl//ruwUTqcguJ7YGs2MXKX5KiMw4NaNJ8+zcSmFGHQFxIcit0/Rw2kP8UP0mm+39flv33Mh5XmP6k0TUZA09sEiDJ/sn+ZrYgXFQtJcqUYnaftybaGY= 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=Ck9qypBU; arc=none smtp.client-ip=91.218.175.186 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="Ck9qypBU" Date: Mon, 6 Apr 2026 12:53:02 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1775505196; 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: in-reply-to:in-reply-to:references:references; bh=IXovqCnmzrS4eafaIE4xviHOkrXx/YXiMKIkCRxRFy8=; b=Ck9qypBUUeubWrUPGT1KdtemkqhN1WZ44o57VDvfufj1WmgJt5zaTSzQ4Kk+PjofRyNJbA ASmdOuiwsBzwk8RZdlw06SUEgTqdiJABpgU5YViHUI7e7LVXa8DZ2N0cul4YdYsqcsJaW9 xlscoPDKRvKpgOXipVgtqvNnJ8bfM+g= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Martin KaFai Lau To: Jiayuan Chen Cc: bpf@vger.kernel.org, Kuniyuki Iwashima , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Eduard Zingerman , Kumar Kartikeya Dwivedi , Song Liu , Yonghong Song , Jiri Olsa , John Fastabend , Stanislav Fomichev , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Shuah Khan , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH bpf v6 1/2] bpf: tcp: Reject non-TCP skb in bpf_sk_assign_tcp_reqsk() Message-ID: <20264619471.he8Q.martin.lau@linux.dev> References: <20260403015851.148209-1-jiayuan.chen@linux.dev> <20260403015851.148209-2-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=us-ascii Content-Disposition: inline In-Reply-To: <20260403015851.148209-2-jiayuan.chen@linux.dev> X-Migadu-Flow: FLOW_OUT On Fri, Apr 03, 2026 at 09:58:27AM +0800, Jiayuan Chen wrote: > bpf_sk_assign_tcp_reqsk() only validates skb->protocol (L3) but does not > check the L4 protocol in the IP header. A BPF program can call this kfunc > on a UDP skb with a valid TCP listener socket, which will succeed and > attach a TCP reqsk to the UDP skb. > > When the UDP skb enters the UDP receive path, skb_steal_sock() returns > the TCP listener from the reqsk. The UDP code then passes this TCP socket > to udp_unicast_rcv_skb() -> __udp_enqueue_schedule_skb(), which casts > it to udp_sock and accesses UDP-specific fields at invalid offsets, > causing a null pointer dereference and kernel panic: > > 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) > > Fix this by checking the IP header's protocol field in > bpf_sk_assign_tcp_reqsk() and rejecting non-TCP skbs with -EINVAL. > > Note that for IPv6, the nexthdr check does not walk extension headers. > This is uncommon for TCP SYN packets in practice, and keeping it simple > was agreed upon by Kuniyuki Iwashima. sashiko has flagged a similar issue with larger scope. Please take a look. Thanks. https://sashiko.dev/#/patchset/20260403015851.148209-1-jiayuan.chen%40linux.dev