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

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Message-ID: <20210629171757.shyr222zjpm6ev5t@example.org>
Date:   Tue, 29 Jun 2021 19:17:57 +0200
From:   Alexey Gladkov <legion@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        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 Mon, Jun 28, 2021 at 08:47:12PM -0700, Linus Torvalds wrote:
> On Mon, Jun 28, 2021 at 3:35 PM Eric W. Biederman <ebiederm@...ssion.com> wrote:
> >
> > This is the work mainly by Alexey Gladkov to limit rlimits to the
> > rlimits of the user that created a user namespace, and to allow users to
> > have stricter limits on the resources created within a user namespace.
> 
> I guess all the performance issues got sorted, since I haven't seen
> any reports from the test robots.
> 
> I do end up with two questions, mainly because of looking at the
> result of the conflict resolution.
> 
> In particular, in __sigqueue_alloc(), two oddities..
> 
> Why the "sigpending < LONG_MAX" test in that
> 
>         if (override_rlimit || (sigpending < LONG_MAX && sigpending <=
> task_rlimit(t, RLIMIT_SIGPENDING))) {
> 
> thing?

inc_rlimit_ucounts() returns long and uses LONG_MAX as an overflow flag.
At the same time, we have increased the size of sigpending from int to
long.

> And why test for "ucounts" being non-NULL in
> 
>                 if (ucounts && dec_rlimit_ucounts(ucounts,
> UCOUNT_RLIMIT_SIGPENDING, 1))
>                         put_ucounts(ucounts);
> 
> when afaik both of those should be happy with a NULL 'ucounts' pointer
> (if it was NULL, we certainly already used it for the reverse
> operations for get_ucounts() and inc_rlimit_ucounts()..)

The get_ucount() can theoretically return NULL. It increments the
reference counter and if it overflows, the function will return NULL.

> Hmm?
> 
> And somebody should verify that I didn't screw anything up in my merge
> resolution. It all looked very straightforward, but mistakes happen..

-- 
Rgrds, legion