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From: ebiederm@xmission.com (Eric W. Biederman)
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Alexey Gladkov <legion@kernel.org>,
	 Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	 Linux Containers <containers@lists.linux.dev>
Subject: Re: [GIT PULL] ucounts: Count rlimits in each user namespace
Date: Tue, 29 Jun 2021 12:09:01 -0500	[thread overview]
Message-ID: <87a6n8simq.fsf@disp2133> (raw)
In-Reply-To: <87mtr8sjvr.fsf@disp2133> (Eric W. Biederman's message of "Tue, 29 Jun 2021 11:42:00 -0500")

ebiederm@xmission.com (Eric W. Biederman) writes:

> Linus Torvalds <torvalds@linux-foundation.org> writes:
>
>> On Tue, Jun 29, 2021 at 8:52 AM Eric W. Biederman <ebiederm@xmission.com> wrote:
>>>
>>> Linus Torvalds <torvalds@linux-foundation.org> writes:
>>>
>>> > Why the "sigpending < LONG_MAX" test in that
>>> >
>>> >         if (override_rlimit || (sigpending < LONG_MAX && sigpending <=
>>> > task_rlimit(t, RLIMIT_SIGPENDING))) {
>>> > thing?
>>>
>>> On second look that sigpending < LONG_MAX check is necessary.  When
>>> inc_rlimit_ucounts detects a problem it returns LONG_MAX.
>>
>> I saw that, but _without_ that test you'd be left with just that
>>
>>     sigpending <= task_rlimit(t, RLIMIT_SIGPENDING)
>>
>> and if task_rlimit() is LONG_MAX, then that means "no limits", so it is all ok.
>
> It means no limits locally.  The creator of your user namespace might
> have had a limit which you are also bound by.
>
> The other possibility is that inc_rlimits_ucounts caused a sigpending
> counter to overflow.  In which case we need to fail and run
> dec_rlimit_ucounts to keep the counter from staying overflowed.
>
> So I don't see a clever way to avoid the sigpending < LONG_MAX  test.

Hmm.  I take that back.  There is a simple clever way to satisfy all of
the tests.

- sigpending < LONG_MAX && sigpending <= task_rlimit(t, RLIMIT_SIGPENDING)
+ sigpending < task_rlimit(t, RLIMIT_SIGPENDING)

That would just need a small comment to explain the subtleties.  

Eric

  reply	other threads:[~2021-06-29 17:09 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-28 22:35 Eric W. Biederman
2021-06-29  3:47 ` Linus Torvalds
2021-06-29 15:04   ` Eric W. Biederman
2021-06-29 15:51   ` Eric W. Biederman
2021-06-29 16:34     ` Linus Torvalds
2021-06-29 16:42       ` Eric W. Biederman
2021-06-29 17:09         ` Eric W. Biederman [this message]
2021-07-01 16:41           ` Alexey Gladkov
2021-07-01 20:05             ` Eric W. Biederman
2021-06-29 17:17   ` Alexey Gladkov
2021-06-29 18:07     ` Linus Torvalds
2021-06-29 20:20       ` Alexey Gladkov
2021-06-29 20:33         ` Linus Torvalds
2021-06-29 21:22           ` Alexey Gladkov
2021-07-02 17:54           ` [PATCH] ucounts: Fix UCOUNT_RLIMIT_SIGPENDING counter leak Alexey Gladkov
2021-07-02 22:13             ` Linus Torvalds
2021-07-07 16:50               ` Alexey Gladkov
2021-07-07 17:23                 ` Linus Torvalds
2021-07-08 10:33                   ` [PATCH v2] " Alexey Gladkov
2021-07-08 18:44                     ` Linus Torvalds
2021-07-08 11:00                   ` [PATCH] ucounts: " Alexey Gladkov
2021-06-29  3:50 ` [GIT PULL] ucounts: Count rlimits in each user namespace pr-tracker-bot

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