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

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Message-ID: <20210701164144.u2dod4g2obfj4kit@example.org>
Date:   Thu, 1 Jul 2021 18:41:44 +0200
From:   Alexey Gladkov <legion@...nel.org>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.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

On Tue, Jun 29, 2021 at 12:09:01PM -0500, Eric W. Biederman wrote:
> ebiederm@...ssion.com (Eric W. Biederman) writes:
> 
> > 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.
> 
> 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.  

Is it because user.sigpending was atomic_t before this patch ?

-- 
Rgrds, legion