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

From: Eric W. Biederman
Date: Tue Jun 29 2021 - 12:42:11 EST

Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> writes:

> On Tue, Jun 29, 2021 at 8:52 AM Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:
>> Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> 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.