linux-kernel - Re: [GIT PULL] ucounts: Count rlimits in each user namespace

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Date:   Tue, 29 Jun 2021 11:42:00 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Alexey Gladkov <legion@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Containers <containers@...ts.linux.dev>
Subject: Re: [GIT PULL] ucounts: Count rlimits in each user namespace

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Tue, Jun 29, 2021 at 8:52 AM Eric W. Biederman <ebiederm@...ssion.com> wrote:
>>
>> Linus Torvalds <torvalds@...ux-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.

Eric