linux-kernel - Re: [PATCH v9 4/8] Reimplement RLIMIT

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Message-ID: <m1eefmjanv.fsf@fess.ebiederm.org>
Date:   Wed, 07 Apr 2021 11:56:36 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Alexey Gladkov <gladkov.alexey@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Jann Horn <jannh@...gle.com>, Jens Axboe <axboe@...nel.dk>,
        Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v9 4/8] Reimplement RLIMIT_NPROC on top of ucounts

Alexey Gladkov <gladkov.alexey@...il.com> writes:

> On Mon, Apr 05, 2021 at 11:56:35AM -0500, Eric W. Biederman wrote:
>>
>> Also when setting ns->ucount_max[] in create_user_ns because one value
>> is signed and the other is unsigned.  Care should be taken so that
>> rlimit_infinity is translated into the largest positive value the
>> type can hold.
>
> You mean like that ?
>
> ns->ucount_max[UCOUNT_RLIMIT_NPROC] = rlimit(RLIMIT_NPROC) <= LONG_MAX ?
> 	rlimit(RLIMIT_NPROC) : LONG_MAX;
> ns->ucount_max[UCOUNT_RLIMIT_MSGQUEUE] = rlimit(RLIMIT_MSGQUEUE) <= LONG_MAX ?
> 	rlimit(RLIMIT_MSGQUEUE) : LONG_MAX;
> ns->ucount_max[UCOUNT_RLIMIT_SIGPENDING] = rlimit(RLIMIT_SIGPENDING) <= LONG_MAX ?
> 	rlimit(RLIMIT_SIGPENDING) : LONG_MAX;
> ns->ucount_max[UCOUNT_RLIMIT_MEMLOCK] = rlimit(RLIMIT_MEMLOCK) <= LONG_MAX ?
> 	rlimit(RLIMIT_MEMLOCK) : LONG_MAX;

Yes.

I only got as far as:
if (rlimit(RLIMI_NNN) == RLIM_INFINITY) {
	ns->ucount_max[UCOUNT_LIMIT_NNN] = LONG_MAX;
} else {
	ns->ucount_max[UCOUNT_LMIT_NNN] = rlmit(RLIMIT_NNN);
}
But forcing everything about LONG_MAX to LONG_MAX actually looks better
in practice.  Especially as that is effectively RLIMIT_INFINITY anyway.

Eric