From: Alexey Gladkov <firstname.lastname@example.org> To: Linus Torvalds <email@example.com> Cc: "Eric W. Biederman" <firstname.lastname@example.org>, Linux Kernel Mailing List <email@example.com>, Linux Containers <firstname.lastname@example.org> Subject: Re: [GIT PULL] ucounts: Count rlimits in each user namespace Date: Tue, 29 Jun 2021 22:20:28 +0200 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <CAHk-=wgcpK3XdFKJ98b_YucXbQMJMgJssAk=sQ-XUo-tyiMjVg@mail.gmail.com> On Tue, Jun 29, 2021 at 11:07:11AM -0700, Linus Torvalds wrote: > On Tue, Jun 29, 2021 at 10:18 AM Alexey Gladkov <firstname.lastname@example.org> wrote: > > > > > > > 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. > > .. but my point is that dec_rlimit_ucounts() and put_ucounts() should > be fine with whatever get_ucounts() returned. No > > It looks like put_ucounts() is unhappy with a NULL ucounts argument, > but I think _that_ is what should get fixed. > > I think that conceptually we should have two clear alternatives: > > (a) either "get_ucounts()" returning NULL should be an error, and we > would have returned long before get_ucounts() in the __sigqueue_alloc() performs the get_uid() function but does not ignore the counter overflow. Basically get_uid() can fail in same way as get_ucounts(), but we just ignore it. > or > > (b) a NULL uncounts is usable, and a sequence like > put_ucounts(get_ucounts()) should just always work. > > And honestly, a lot of the other ucounts funcrtions seem to take that > (b) approach. Example in that very function: > > ucounts = task_ucounts(t); > sigpending = inc_rlimit_ucounts(ucounts, UCOUNT_RLIMIT_SIGPENDING, 1); > > which at no point tested for NULL or returned an error. Waaaait. task_ucounts() is a different thing. This function only gets a field from the task structure without any reference counting. But the get_ucounts() is more like get_user_ns() or get_uid(), but does not ignore counter overflow. Earlier I tried to use refcount_t which never returns errors . We talked and you said that ignoring counter overflow errors is bad design for this case. > (And that also implies that the comment in dec_rlimit_ucounts() about > "Silence compiler warning" should just go away, because it's not just > a compiler warning, it's a required initialization). > > Linus  https://lore.kernel.org/lkml/CAHk-%3dwjYOCgM%2bmKzwTZwkDDg12DdYjFFkmoFKYLim7NFmR9HBg@mail.gmail.com/ -- Rgrds, legion
next prev parent reply other threads:[~2021-06-29 20:20 UTC|newest] Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-06-28 22:35 Eric W. Biederman 2021-06-29 3:47 ` Linus Torvalds 2021-06-29 15:04 ` Eric W. Biederman 2021-06-29 15:51 ` Eric W. Biederman 2021-06-29 16:34 ` Linus Torvalds 2021-06-29 16:42 ` Eric W. Biederman 2021-06-29 17:09 ` Eric W. Biederman 2021-07-01 16:41 ` Alexey Gladkov 2021-07-01 20:05 ` Eric W. Biederman 2021-06-29 17:17 ` Alexey Gladkov 2021-06-29 18:07 ` Linus Torvalds 2021-06-29 20:20 ` Alexey Gladkov [this message] 2021-06-29 20:33 ` Linus Torvalds 2021-06-29 21:22 ` Alexey Gladkov 2021-07-02 17:54 ` [PATCH] ucounts: Fix UCOUNT_RLIMIT_SIGPENDING counter leak Alexey Gladkov 2021-07-02 22:13 ` Linus Torvalds 2021-07-07 16:50 ` Alexey Gladkov 2021-07-07 17:23 ` Linus Torvalds 2021-07-08 10:33 ` [PATCH v2] " Alexey Gladkov 2021-07-08 18:44 ` Linus Torvalds 2021-07-08 11:00 ` [PATCH] ucounts: " Alexey Gladkov 2021-06-29 3:50 ` [GIT PULL] ucounts: Count rlimits in each user namespace pr-tracker-bot
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