linux-kernel - Re: [PATCH 3/8] ucounts: Fix and simplify RLIMIT

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Message-ID: <20220215102518.GE21589@blackbody.suse.cz>
Date:   Tue, 15 Feb 2022 11:25:18 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Solar Designer <solar@...nwall.com>, linux-kernel@...r.kernel.org,
        Alexey Gladkov <legion@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Shuah Khan <shuah@...nel.org>,
        Christian Brauner <brauner@...nel.org>,
        Ran Xiaokai <ran.xiaokai@....com.cn>, stable@...r.kernel.org
Subject: Re: [PATCH 3/8] ucounts: Fix and simplify RLIMIT_NPROC handling
 during setuid()+execve

On Mon, Feb 14, 2022 at 09:10:49AM -0600, "Eric W. Biederman" <ebiederm@...ssion.com> wrote:
> I really like how cleanly this patch seems to be.  Unfortunately it is
> wrong.

It seems [1] so:

setuid()		// RLIMIT_NPROC is fine at this moment
...		fork()
		...
...		fork()
execve()		// eh, oh

This "punishes" the exec'ing task although the cause is elsewhere.

Michal

[1] The decoupled setuid()+execve() check can be interpretted both ways.
I understood historically the excess at the setuid() moment is relevant.