On Tue, Jun 29, 2021 at 11:07:11AM -0700, Linus Torvalds wrote: > On Tue, Jun 29, 2021 at 10:18 AM Alexey Gladkov <legion@xxxxxxxxxx> 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 [1]. 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 [1] https://lore.kernel.org/lkml/CAHk-%3dwjYOCgM%2bmKzwTZwkDDg12DdYjFFkmoFKYLim7NFmR9HBg@xxxxxxxxxxxxxx/ -- Rgrds, legion
