blk-mq: release crypto keyslot before reporting I/O complete

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: blk-mq: release crypto keyslot before reporting I/O complete Once all I/O using a blk_crypto_key has completed, filesystems can call blk_crypto_evict_key(). However, the block layer currently doesn't call blk_crypto_put_keyslot() until the request is being freed, which happens after upper layers have been told (via bio_endio()) the I/O has completed. This causes a race condition where blk_crypto_evict_key() can see 'slot_refs != 0' without there being an actual bug. This makes __blk_crypto_evict_key() hit the 'WARN_ON_ONCE(atomic_read(&slot->slot_refs) != 0)' and return without doing anything, eventually causing a use-after-free in blk_crypto_reprogram_all_keys(). (This is a very rare bug and has only been seen when per-file keys are being used with fscrypt.) There are two options to fix this: either release the keyslot before bio_endio() is called on the request's last bio, or make __blk_crypto_evict_key() ignore slot_refs. Let's go with the first solution, since it preserves the ability to report bugs (via WARN_ON_ONCE) where a key is evicted while still in-use.

References

• https://git.kernel.org/stable/c/874bdf43b4a7dc5463c31508f62b3e42eb237b08
• https://git.kernel.org/stable/c/d206f79d9cd658665b37ce8134c6ec849ac7af0c
• https://git.kernel.org/stable/c/7d206ec7a04e8545828191b6ea8b49d3ea61391f
• https://git.kernel.org/stable/c/b278570e2c59d538216f8b656e97680188a8fba4
• https://git.kernel.org/stable/c/92d5d233b9ff531cf9cc36ab4251779e07adb633
• https://git.kernel.org/stable/c/9cd1e566676bbcb8a126acd921e4e194e6339603