linux-kernel - Re: packet: Improve exception handling in fanout

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date: Mon, 01 Jan 2024 10:29:21 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Markus Elfring <Markus.Elfring@....de>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>, 
 netdev@...r.kernel.org, 
 kernel-janitors@...r.kernel.org, 
 "David S. Miller" <davem@...emloft.net>, 
 Eric Dumazet <edumazet@...gle.com>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>, 
 Stephen Hemminger <stephen@...workplumber.org>
Cc: LKML <linux-kernel@...r.kernel.org>
Subject: Re: packet: Improve exception handling in fanout_add()

Markus Elfring wrote:
> > It is fine to call kfree with a possible NULL pointer:
> …
> > 	 * If @object is NULL, no operation is performed.
> > 	 */
> > 	void kfree(const void *object)
> 
> Such a function call triggers an input parameter validation
> with a corresponding immediate return, doesn't it?
> Do you find such data processing really helpful for the desired error/exception handling?

It's not just personal preference. It is an established pattern to
avoid extra NULL tests around kfree.

A quick git log to show a few recent examples of patches that expressly
remove such branches, e.g.,

commit d0110443cf4a ("amd/pds_core: core: No need for Null pointer check before kfree")
commit efd9d065de67 ("drm/radeon: Remove unnecessary NULL test before kfree in 'radeon_connector_free_edid'")

An interesting older thread on the topic:

https://linux-kernel.vger.kernel.narkive.com/KVjlDsTo/kfree-null

My summary, the many branches scattered throughout the kernel likely
are more expensive than the occasional save from seeing the rare NULL
pointer.