CVE-2024-35797 Information

May 18, 2024 cve

Description

In the Linux kernel the following vulnerability has been resolved:

mm: cachestat: fix two shmem bugs

When cachestat on shmem races with swapping and invalidation there are two possible bugs:

A swapin error can have resulted in a poisoned swap entry in the shmem inode’s xarray. Calling get_shadow_from_swap_cache() on it will result in an out-of-bounds access to swapper_spaces[].

Validate the entry with non_swap_entry() before going further.
When we find a valid swap entry in the shmem’s inode the shadow entry in the swapcache might not exist yet: swap IO is still in progress and we’re before __remove_mapping; swapin invalidation or swapoff have removed the shadow from swapcache after we saw the shmem swap entry.

This will send a NULL to workingset_test_recent(). The latter purely operates on pointer bits so it won’t crash - node 0 memcg ID 0 eviction timestamp 0 etc. are all valid inputs - but it’s a bogus test. In theory that could result in a false ecently evicted\ count.

Such a false positive wouldn’t be the end of the world. But for code clarity and (future) robustness be explicit about this case.

Bail on get_shadow_from_swap_cache() returning NULL.

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