Messages in this thread | | | From | (Eric W. Biederman) | Date | Thu, 01 Jul 2021 15:05:18 -0500 | Subject | Re: [GIT PULL] ucounts: Count rlimits in each user namespace |
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Alexey Gladkov <legion@kernel.org> writes:
> On Tue, Jun 29, 2021 at 12:09:01PM -0500, Eric W. Biederman wrote: >> 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. > > Is it because user.sigpending was atomic_t before this patch ?
Apologies I was wrong.
The replacement of "<=" with "<" is correct for the case where "task_rlimit(t, RLIMIT_SIGPENDING) == LONG_MAX".
Unfortunately off by one for all other values of "task_rlimit(t, RLIMIT_SIGPENDING)".
It completely breaks things for the case where RLIMIT_SIGPENDING == 1, where no signals are allowed to be queued. Today allowing 1 queued signal with a single task and a sender that does not send a second signal until the first is consumed will work reliably.
That was just a brain fart on my part.
Eric
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