From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 9A822363081; Tue, 18 Aug 2026 15:50:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787068226; cv=none; b=CeYqHi/O7/s1rKOHXkaWnr8vpOITslUiryIEZVZl/ftXHrcK2rZDlkT4FtVjQUnvH6QVA2HiMTqEkKiBXeMT6/RZLgTP+EJup/4gD/2oJhwEW5bajluQoapA6/B3uX/B7VJPV5fqSrR4Qxi5iZ7FCYhPeOXKsSVE1CEbfVbFiZU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787068226; c=relaxed/simple; bh=nlp08hHGiLccYDf+/XVoWlrGj7xR3CL2bOzNqCOBPcE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=UINsMhOC0aAhKLP7lBTbedZLgMpI/UyFtif73xZvtXkg3P0qVWnGlEcVLK4cMpAvy6lnaTLknOjqtRQwewHMyrPyyd2sjMEEQVJk3d4Qz7lozgAnLMhuWKs0zqsRhTP6R/jnbj69i8RGOFMfVuZPpFtlUhYB+sKJHO1MjKvSjys= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GUUn+o8Y; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="GUUn+o8Y" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7187D1F000E9; Tue, 18 Aug 2026 15:50:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787068225; bh=fGoucq703kpQy1vL6rg4U4eLvWWv4LLJ5Mwz/r7MHdM=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=GUUn+o8YfLndQshOnVo/EoBsAZy7ZWyNkxpUo6O4dzPCgQIROeK+o+8W/77hLUhJT bvT7roxyeEJh34ljNR/GbUBPa8spjcOYF3GiLoGo0WV36E1Q/V/QWj2I5MreTaiWqj HYGyPn3hZsAzwgXL0m4YQXhXP4ISFHK8On/B3SoK9VRqVF+D1sj+08c2ONXoJAQj7g Q4Kh6OsmIuBI5myWf20R741aPLBx9+aqJmJIl8UA39lw/Ay8w3ZbmSekOqB8btlq5f DVJxKU/4oml7JWnE1z5fCaaHFy1O4w3s6tYbg+9d51h5vsz/wT9+ysWqGQEieuWC8h +ZqnbzNRSNkfA== Message-ID: Date: Tue, 18 Aug 2026 17:50:21 +0200 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH mptcp-next v2 1/5] mptcp: sched: change scheduler sysctl atomically Content-Language: fr To: gang.yan@linux.dev, sashiko-reviews@lists.linux.dev Cc: mptcp@lists.linux.dev References: <20260818094825.48446-1-gang.yan@linux.dev> <20260818094825.48446-2-gang.yan@linux.dev> <20260818095955.6892E1F000E9@smtp.kernel.org> From: Matthieu Baerts Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Gang, On 18/08/2026 14:56, gang.yan@linux.dev wrote: > August 18, 2026 at 5:59 PM, sashiko-bot@kernel.org mailto:sashiko-bot@kernel.org wrote: > > >> >> Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider: >> - [High] Use-After-Free and module reference leak due to missing reference counting when setting the default MPTCP scheduler >> - [Medium] Redundant scheduler list traversal during socket initialization defeats pointer caching >> -- >> >> --- Patch [1]: [PATCH mptcp-next v2 1/5] mptcp: sched: change scheduler sysctl atomically --- >> commit d5b1780c033b9909a1b30fbd814812af5c25ed2f >> Author: Gang Yan >> >> mptcp: sched: change scheduler sysctl atomically >> >> This commit changes the per-netns scheduler storage from an inline string >> to an RCU-protected pointer to an mptcp_sched_ops struct. It updates the >> sysctl read/write paths and socket initialization to use this pointer, >> aiming to prevent concurrent readers from observing half-written names. >> >> Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/626 >> >>> >>> diff --git a/net/mptcp/ctrl.c b/net/mptcp/ctrl.c >>> index 63c5747f0f63c..479b31eb30079 100644 >>> --- a/net/mptcp/ctrl.c >>> +++ b/net/mptcp/ctrl.c >>> >> [ ... ] >> >>> >>> @@ -126,7 +133,7 @@ static int mptcp_set_scheduler(char *scheduler, const char *name) >>> rcu_read_lock(); >>> sched = mptcp_sched_find(name); >>> if (sched) >>> - strscpy(scheduler, name, MPTCP_SCHED_NAME_MAX); >>> + xchg(&pernet->scheduler, sched); >>> >> [Severity: High] >> When replacing the scheduler pointer here with xchg(), does this leak the >> module reference for the previous scheduler returned by xchg()? >> >> Also, do we need to acquire a module reference for the newly assigned sched >> via bpf_try_module_get() before storing it? Without a reference, could the >> module be unloaded, leaving pernet->scheduler pointing to freed memory that >> would trigger a use-after-free when dereferenced by a concurrent reader in >> proc_scheduler()? > > Hi Matt, (you can address such email to the list, I'm not the only one here ;) ) > As far as I know, for linux-master branch, the sched ops cannot be torndown, and > the only static default scheduler is used, so no reference counting is needed. Thank you for replying to these emails from Sashiko, that's the right way to do! > It is safe for now, the pm is as the same. Right? Oh, sorry, I just realised the BPF module part for the scheduler is already in Linux mainstream [1], but not the PM one [2]: [1] https://elixir.bootlin.com/linux/v7.2/source/net/mptcp/sched.c#L130-L160 [2] https://elixir.bootlin.com/linux/v7.2/source/net/mptcp/pm.c#L1225-L1254 Sorry for the confusion, but then I guess the split is only needed for the PM side. In fact patch 1/3 from the v1 can apply on net-next directly. So in terms of split, the sched part from v1 was OK (no split), but for the PM, we need the split from v2. Cheers, Matt -- Sponsored by the NGI0 Core fund.