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 - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
