linux-kernel - Re: [PATCH 5/8] ucounts: Handle wrapping in is_ucounts

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Message-ID: <20220215112541.GH21589@blackbody.suse.cz>
Date:   Tue, 15 Feb 2022 12:25:41 +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 5/8] ucounts: Handle wrapping in is_ucounts_overlimit

On Mon, Feb 14, 2022 at 09:23:09AM -0600, "Eric W. Biederman" <ebiederm@...ssion.com> wrote:
> Pretty much. The function essentially only exists so that we can
> handle the weirdness of RLIMIT_NPROC.
> Now that I have discovered the
> weirdness of RLIMIT_NPROC is old historical sloppiness I expect the
> proper solution is to rework how RLIMIT_NPROC operates and to remove
> is_ucounts_overlimit all together.

The fork path could make do with some kind of atomic add+check (similar
to inc_ucounts) and overflows would be sanitized by that. (Seems to
apply to other former RLIMIT_* per-user counters too.)

The is_ucounts_overlimit() and overflowable increment indeed appears
necessary only to satisfy the set*uid+execve pair.

For the sake of bug-fixing, both the patches 5/8 and 6/8 can have 
Reviewed-by: Michal Koutný <mkoutny@...e.com>


Michal