Messages in this thread | | | Subject | Re: [PATCH] genirq: fix reference leaks on irq affinity notifiers | From | Ben Hutchings <> | Date | Tue, 17 Mar 2020 14:56:46 +0000 |
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On Tue, 2020-03-17 at 10:58 +0000, Edward Cree wrote: > On 15/03/2020 20:29, Ben Hutchings wrote: > > ...since the pending work item holds a reference to the notification > > state, it's still not clear to me why or whether "genirq: Prevent use- > > after-free and work list corruption" was needed. > Yeah, I think that commit was bogus. The email thread[1] doesn't > exactly inspire confidence either. I think the submitter just didn't > realise that there was a ref corresponding to the work; AFAICT there's > no way the alleged "work list corruption" could happen. > > > If it's reasonable to cancel_work_sync() when removing a notifier, I > > think we can remove the kref and call the release function directly. > I'd prefer to stick to the smaller fix for -rc and stable. But if you > want to remove the kref for -next, I'd be happy to Ack that patch.
OK, then you can add:
Acked-by: Ben Hutchings <ben@decadent.org.uk>
to this one.
> Btw, we (sfc linux team) think there's still a use-after-free issue in > the cpu_rmap lib, as follows: > 1) irq_cpu_rmap_add creates a glue and notifier, adds glue to rmap->obj > 2) someone else does irq_set_affinity_notifier. > This causes cpu_rmap's notifier (old_notify) to get released, and so > irq_cpu_rmap_release kfrees glue. But it's still in rmap->obj > 3) free_irq_cpu_rmap loops over obj, finds the glue, tries to clear its > notifier. > Now one could say that this UAF is academic, since having two bits of > code trying to register notifiers for the same IRQ is broken anyway > (in this case, the rmap would stop getting updated, because the > "someone else" stole the notifier).
So far as I can remember, my thinking was that only non-shared IRQs will have notifiers and only the current user of the IRQ will set the notifier. The doc comment for irq_set_affinity_notifier() implies the latter restriction, but it might be worth spelling this out explicitly.
Ben.
> But I thought I'd bring it up in case it's halfway relevant. > > -ed > > [1] https://lore.kernel.org/lkml/1553119211-29761-1-git-send-email-psodagud@codeaurora.org/T/#u -- Ben Hutchings For every complex problem there is a solution that is simple, neat, and wrong.
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