Entreprise française de cybersécurité depuis 2004
☎ 03 60 47 09 81 - info@securiteinfo.com
☎ 03 60 47 09 81 - info@securiteinfo.com
In the Linux kernel, the following vulnerability has been resolved:perf/core: Prevent VMA split of buffer mappingsThe perf mmap code is careful about mmap()'ing the user page with theringbuffer and additionally the auxiliary buffer, when the event supportsit. Once the first mapping is established, subsequent mapping have to usethe same offset and the same size in both cases. The reference counting forthe ringbuffer and the auxiliary buffer depends on this being correct.Though perf does not prevent that a related mapping is split via mmap(2),munmap(2) or mremap(2). A split of a VMA results in perf_mmap_open() calls,which take reference counts, but then the subsequent perf_mmap_close()calls are not longer fulfilling the offset and size checks. This leads toreference count leaks.As perf already has the requirement for subsequent mappings to match theinitial mapping, the obvious consequence is that VMA splits, caused byresizing of a mapping or partial unmapping, have to be prevented.Implement the vm_operations_struct::may_split() callback and returnunconditionally -EINVAL.That ensures that the mapping offsets and sizes cannot be changed after thefact. Remapping to a different fixed address with the same size is stillpossible as it takes the references for the new mapping and drops those ofthe old mapping.
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