Messages in this thread | | | Date | Fri, 30 Aug 2019 16:40:23 +0100 | From | Russell King - ARM Linux admin <> | Subject | Re: [BUG] Use of probe_kernel_address() in task_rcu_dereference() without checking return value |
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On Fri, Aug 30, 2019 at 08:30:00AM -0700, Linus Torvalds wrote: > On Fri, Aug 30, 2019 at 7:08 AM Russell King - ARM Linux admin > <linux@armlinux.org.uk> wrote: > > > > which means that when probe_kernel_address() returns -EFAULT, the > > destination is left uninitialised. In the case of > > task_rcu_dereference(), this means that "siginfo" can be used without > > having been initialised, resulting in this function returning an > > indeterminant result (based on the value of an uninitialised variable > > on the stack.) > > Do you actually see that behavior?
No, it was an observation of the code.
> Because the foillowing lines: > > smp_rmb(); > if (unlikely(task != READ_ONCE(*ptask))) > goto retry; > > are what is supposed to protect it - yes, it could have faulted, but > only if 'task' isn't valid any more, and we just re-checked it.
Ah, ok. Might be worth some comments - I find the comments in that function particularly unhelpful (even after Oleg mentions this is case 2.)
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