Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH] exit: Put an upper limit on how often we can oops | Date | Tue, 8 Nov 2022 09:26:06 +0000 |
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From: Jann Horn > Sent: 07 November 2022 20:13 > > Many Linux systems are configured to not panic on oops; but allowing an > attacker to oops the system **really** often can make even bugs that look > completely unexploitable exploitable (like NULL dereferences and such) if > each crash elevates a refcount by one or a lock is taken in read mode, and > this causes a counter to eventually overflow. > > The most interesting counters for this are 32 bits wide (like open-coded > refcounts that don't use refcount_t). (The ldsem reader count on 32-bit > platforms is just 16 bits, but probably nobody cares about 32-bit platforms > that much nowadays.) > > So let's panic the system if the kernel is constantly oopsing.
I think you are pretty much guaranteed to run out of memory (or at least KVA) before any 32bit counter wraps.
That is probably even harder to diagnose than a refcount wrap!
David
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