linux-kernel - Re: [PATCH] kernel/groups.c: use bsearch library function

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Message-ID: <60e43953-a7f9-c52e-150c-74059d1b377b@rasmusvillemoes.dk>
Date:   Wed, 9 Oct 2019 09:46:21 +0200
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Thomas Meyer <thomas@...3r.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kernel/groups.c: use bsearch library function

On 07/10/2019 21.26, Thomas Meyer wrote:
> commit b7b2562f7252 ("kernel/groups.c: use sort library function")
> introduced the sort library function.
> also use the bsearch library function instead of open-coding the binary
> search.

Yes, but please note the difference between sorting the group_info and
searching it: The former is done quite rarely - the setgroups syscall is
used roughly once per login-session.

But the searching of that structure is done more or less every time a
user accesses a file not owned by that user (e.g., any time a normal
user accesses anything in /usr) - at least if I'm reading
acl_permission_check() right.

So using a callback-based interface, especially in a post-spectre world,
may have a somewhat large performance impact.

Rasmus