From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 66E3139B952; Tue, 5 May 2026 15:14:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777994053; cv=none; b=L0O5NtIQ4pgvMm7c+Idtb4sL5+B0OTS5x0nK25zYVtzv8jRM/SUxdiue/cnyIGYs/MGnNYsX96XLjVvQ52Wb61+qbNfk+ZrQ5AXcJej6jxEoCwBzIl7AGGGjjp4vzecR8AeIETZevAOitmDk0sdxnCkkOvqd4zBOURzMnUIbcOg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777994053; c=relaxed/simple; bh=yJ/mQCKDNyWieksngGmTrHElKRuZ0mOGGcnfFjZfoqk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=W2T+JgacibGB6y1EKnDcgzTz94XO6KrQhZSIilU4MxP0J2rLhXn9XZlGqn0GhVfktKwu9evANrAmWR336A+aVSqDiTweEjg62+zBVqRZ34mHwRDPxF0d+s+yB5X+3CTVQFQ3bR5zMumPGX/pHXoRJLdGOV8qeScudZCBhqtmNXM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=eqMQr+8E; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="eqMQr+8E" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 87951C2BCB4; Tue, 5 May 2026 15:14:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777994053; bh=yJ/mQCKDNyWieksngGmTrHElKRuZ0mOGGcnfFjZfoqk=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=eqMQr+8EBUJ65SoEkkHVJK8O4j3mVUGSiFlBXcji5jIKi+gn7xoGcTfrt4UF7m9h5 1xTyCxkWlU2Qlr+INPcwtfdEA0Wuqfmi50hFZgdN5FeCe+6+Q/jmz86p5YrjHMpRT5 pOzGG2HwqocyR8wIzTEBJEAp4mp/18pUPAEe77F47mCJ0LOAcxP/1H385YJd160Qul DfboSff+xTkwSR6ucKFpr5yHv7+FlASzLzGfXMecYe0tyNO8lry9sF+yUqyfCwxz8+ LLVa4TBrDWB0e0cTs+HiMWMQZ5m6QkAeHuZHgvmFLvU7SO/4QDgTqzj3JWeTjqmGl1 1k2ulheBiDS/g== Message-ID: <64a691f2-4104-4538-9aa6-6feadc756c56@kernel.org> Date: Tue, 5 May 2026 17:14:08 +0200 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH v2 bpf 3/6] mptcp: bpf: fix type confusion in bpf_mptcp_sock_from_subflow() Content-Language: fr To: Kuniyuki Iwashima , sashiko@lists.linux.dev Cc: bpf@vger.kernel.org, MPTCP Linux References: <20260504210610.180150-4-kuniyu@google.com> <20260505041435.187D0C2BCB4@smtp.kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit Hi Kuniyuki, (+cc MPTCP ML) On 05/05/2026 07:43, Kuniyuki Iwashima wrote: > Could you follow up on the comments by Sashiko ? Thank you for having forwarded this! > On Mon, May 4, 2026 at 9:14 PM wrote: (...) >>> diff --git a/net/mptcp/bpf.c b/net/mptcp/bpf.c >>> index 8a16672b94e2..4cc16cbeb328 100644 >>> --- a/net/mptcp/bpf.c >>> +++ b/net/mptcp/bpf.c >>> @@ -14,7 +14,7 @@ >>> >>> struct mptcp_sock *bpf_mptcp_sock_from_subflow(struct sock *sk) >>> { >>> - if (sk && sk_fullsock(sk) && sk->sk_protocol == IPPROTO_TCP && sk_is_mptcp(sk)) >>> + if (sk && sk_fullsock(sk) && sk_is_tcp(sk) && sk_is_mptcp(sk)) >>> return mptcp_sk(mptcp_subflow_ctx(sk)->conn); >> >> Could this cause a regression by dereferencing a NULL pointer when accessed >> concurrently? >> >> In subflow_ulp_fallback(), icsk->icsk_ulp_data is set to NULL prior to >> clearing tcp_sk(sk)->is_mptcp. If a BPF program triggers in this window, >> sk_is_mptcp() would return true but mptcp_subflow_ctx(sk) would return NULL, >> leading to a NULL pointer dereference. This would need to be confirmed, but from what I see, that's not a new bug introduced by the patch here. >> Additionally, could ctx->conn be NULL when read here? >> >> During subflow_ulp_init(), the context is allocated and is_mptcp is set to 1, >> but ctx->conn is initially NULL. Passing NULL to mptcp_sk(ctx->conn) triggers >> a kernel panic on CONFIG_DEBUG_NET builds. On non-debug builds, it returns a >> non-NULL offset pointer, which bypasses BPF verifier NULL checks and causes >> invalid memory accesses. Same here: not a new bug. >> Could this introduce a regression with a use-after-free of the mptcp_sock >> during teardown? >> >> During subflow_ulp_release(), sock_put(ctx->conn) drops the reference to the >> parent mptcp_sock and may free it. However, ctx->conn is not cleared, and the >> subflow context remains valid until the RCU grace period ends. >> >> If a BPF tracing program triggers after sock_put(), could this retrieve >> and return the dangling ctx->conn pointer, enabling the BPF program to read >> from freed kernel slab memory? Same here: not a new bug. Sashiko is good at finding potential existing bugs that predate a patch, which is good, but someone has to fix them :) Because the issues raised here are not new, I suggest not blocking this patch. I will check if someone can look at it quickly. Cheers, Matt -- Sponsored by the NGI0 Core fund.