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 C2C6269D39 for ; Wed, 31 Jan 2024 11:12:58 +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=1706699578; cv=none; b=sFln8Njc5YRq17yLzWqn9MkLF22Fl7+jO+omJkg13GUIadfLaxHeUEdqWPZQ+a8ym3jWR4ftf4k5Uo7vXrn0gp0tLSsPyLZ56fwUHDrxgtyLjKScggfutmfl8WI9qEfqWP7lT6jllDJBXJzfXtFbvCUn+ER0vhbAo0jX6NR1MzI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706699578; c=relaxed/simple; bh=tEOBy/Wdn8oHi3sr0IWHYknQLM1yVJ7ADq9IGVUkJp0=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=bFZL2RtI16gW7dyJBYfBeDrIym2UfvdkPEN5Z7UAmuR1ih0GzSJ1aTI9IOWLevYiW7+K2kuhGREALRqzWLlaNeBq1njhemfLbThJWVYuEaj80J3tv7lWggEDrwS5sJe7eKLUM1ycqfrGOJe0kOdDxKGS4XQi5WX6tHM6uinUkno= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=UuSQeVTu; 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="UuSQeVTu" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B657FC43390; Wed, 31 Jan 2024 11:12:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1706699578; bh=tEOBy/Wdn8oHi3sr0IWHYknQLM1yVJ7ADq9IGVUkJp0=; h=Date:Subject:To:References:From:In-Reply-To:From; b=UuSQeVTuG32TwXA8uPemK/GBUoq/xSyNK+jpDahVlKd5lIHPo+l0+NgaaFIh6Hh1I UlEhIq7O9T01lC5qaKW+2QqCj3GaHXwK+d1AJ2xv5LW/tdUMF6OgJqOw+asBxYgVH+ +13AGkOIwgzTakDyFSFUNXW+HvYxNy0rUM9dESxBxsCdR+DZUZmKWaKjmDTxM7ZuEj Os7/Ps9NmSbEGhm2moDcKezfbYwg2f4LBw6AgwAvBX3lOSIU14HAT8YjQbwoTgYbuL FAUF25X06hc8lclOdiItTVbZbHyvvb1351BpR3ZzF1ponp2+gbp3Kj/Zg/i1u4ful+ ECppeJ9gpuoqg== Message-ID: <08f4ba4e-e17b-40fd-874d-d4428a2c0b68@kernel.org> Date: Wed, 31 Jan 2024 12:12:56 +0100 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH mptcp-net] mptcp: fix data re-injection from stale subflow Content-Language: en-GB, fr-BE To: Paolo Abeni , mptcp@lists.linux.dev References: <35875ef9cb7194563b580e14c71cc8cb065f846c.1706043786.git.pabeni@redhat.com> <39a0fa5f-03e2-4ef3-90b7-decd8971905b@kernel.org> <195dfb64e0e8ecfac60c8f29df9e61c1c7cfea17.camel@redhat.com> <762d499c-1f90-470e-8e3f-b26eafd519dc@kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Paolo, On 30/01/2024 19:53, Paolo Abeni wrote: > On Tue, 2024-01-30 at 18:52 +0100, Matthieu Baerts wrote: >> Hi Paolo, >> >> Thank you for your reply! >> >> On 30/01/2024 16:12, Paolo Abeni wrote: >>> On Tue, 2024-01-30 at 12:59 +0100, Matthieu Baerts wrote: >>>> Hi Paolo, Mat, >>>> >>>> On 23/01/2024 22:03, Paolo Abeni wrote: >>>>> When the MPTCP PM detects that a subflow is stale, all the packet >>>>> scheduler must re-inject all the mptcp-level unacked data. To avoid >>>>> acquiring unneeded locks, it first try to check if any unacked data >>>>> is present at all in the RTX queue, but such check is currently >>>>> broken, as it uses TCP-specific helper on an MPTCP socket. >>>>> >>>>> Funnily enough fuzzers and static checkers are happy, as the accessed >>>>> memory still belongs to the mptcp_sock struct, and even from a >>>>> functional perspective the recovery completed successfully, as >>>>> the short-cut test always failed. >>>>> >>>>> A recent unrelated TCP change - commit d5fed5addb2b ("tcp: reorganize >>>>> tcp_sock fast path variables") - exposed the issue, as the tcp field >>>>> reorganization makes the mptcp code always skip the re-inection. >>>>> >>>>> Fix the issue dropping the bogus call: we are on a slow path, the early >>>>> optimization proved once again to be evil. >>>>> >>>>> Fixes: 1e1d9d6f119c ("mptcp: handle pending data on closed subflow") >>>>> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/468 >>>>> Signed-off-by: Paolo Abeni >>>> >>>> Thank you for the patch and the review! >>>> >>>> Any ideas how to prevent such issues? Changing the signature of the >>>> TCP-specific functions? Adding a custom check for our CI on our side? >>> >>> I guess we could add debug-only code in mptcp_sk() and in tcp_sk() >>> checking that the argument pointer belongs to the relevant slab, see >>> kfree(): >>> >>> https://elixir.bootlin.com/linux/v6.8-rc2/source/mm/slub.c#L4407 >>> >>> we could fetch slab->slab_cache and check it vs >>> mptcp_v6_prot.slab/mptcp_prot.slab/tcp_prot.slab/tcpv6_prot.slab. >>> >>> The main downside is that such code is heavily mm-dependent and may >>> change/break when upstream progresses. >> >> Good idea! >> >> If you think it is too fragile, maybe we could add a new entry in >> "struct inet_connection_sock" (or "struct sock"?) -- e.g. is_msk --, set >> it in mptcp_init_sock(), and check it in mptcp_sk() and in tcp_sk(). > > Nice! that would be much more robust! Thinking again about it, we could > simply check: > > sk->sk_prot == mptcp_prot || sk->sk_prot == mptcp_v6_prot Nice! What about adding this in tcp_sk(): WARN_ON(sk->sk_protocol != IPPROTO_TCP); and this in mptcp_sk(): WARN_ON(sk->sk_protocol != IPPROTO_MPTCP); But then I suppose we will need to have these two helpers inlined when we want to use this debug option. They are no longer inlined since: - e9d9da91548b ("tcp: preserve const qualifier in tcp_sk()") - 403a40f2304d ("mptcp: preserve const qualifier in mptcp_sk()") >> We can do that only if KASAN kconfig is set (or another one?). > > A possible option could be DEBUG_NET, but such option currently enables > almost no-overhead things. I think we can use it, if we opt for > checking sk_prot. Sounds good to me! Do you think this kind of patch could even be upstreamed? We can suggest it and see. Cheers, Matt -- Sponsored by the NGI0 Core fund.