linux-kernel - Re: [PATCH net-next] mptcp: pm: Fix undefined behavior in mptcp_remove_anno_list_by

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Message-Id: <7EEE7001-CCD4-4A5A-8723-3AAC3A88F6FF@linux.dev>
Date: Tue, 25 Mar 2025 13:51:28 +0100
From: Thorsten Blum <thorsten.blum@...ux.dev>
To: Jakub Kicinski <kuba@...nel.org>
Cc: Matthieu Baerts <matttbe@...nel.org>,
 Mat Martineau <martineau@...nel.org>,
 Geliang Tang <geliang@...nel.org>,
 "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>,
 netdev@...r.kernel.org,
 mptcp@...ts.linux.dev,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] mptcp: pm: Fix undefined behavior in
 mptcp_remove_anno_list_by_saddr()

On 25. Mar 2025, at 13:30, Jakub Kicinski wrote:
> On Tue, 25 Mar 2025 12:33:11 +0100 Thorsten Blum wrote:
>> On 25. Mar 2025, at 12:06, Thorsten Blum wrote:
>>> 
>>> Commit e4c28e3d5c090 ("mptcp: pm: move generic PM helpers to pm.c")
>>> removed a necessary if-check, leading to undefined behavior because
>>> the freed pointer is subsequently returned from the function.
>>> 
>>> Reintroduce the if-check to fix this and add a local return variable to
>>> prevent further checkpatch warnings, which originally led to the removal
>>> of the if-check.
>>> 
>>> Fixes: e4c28e3d5c090 ("mptcp: pm: move generic PM helpers to pm.c")
>>> Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
>>> ---  
>> 
>> Never mind, technically it's not actually undefined behavior because of
>> the implicit bool conversion, but returning a freed pointer still seems
>> confusing.
> 
> CCing the list back in.

Thanks!

The change imo still makes sense, but the commit message should be
updated. I'll submit a new patch for after the merge window.