blk-crypto: make blk_crypto_evict_key() more robust

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: blk-crypto: make blk_crypto_evict_key() more robust If blk_crypto_evict_key() sees that the key is still in-use (due to a bug) or that ->keyslot_evict failed, it currently just returns while leaving the key linked into the keyslot management structures. However, blk_crypto_evict_key() is only called in contexts such as inode eviction where failure is not an option. So actually the caller proceeds with freeing the blk_crypto_key regardless of the return value of blk_crypto_evict_key(). These two assumptions don't match, and the result is that there can be a use-after-free in blk_crypto_reprogram_all_keys() after one of these errors occurs. (Note, these errors *shouldn't* happen; we're just talking about what happens if they do anyway.) Fix this by making blk_crypto_evict_key() unlink the key from the keyslot management structures even on failure. Also improve some comments.

References

• https://git.kernel.org/stable/c/701a8220762ff90615dc91d3543f789391b63298
• https://git.kernel.org/stable/c/5bb4005fb667c6e2188fa87950f8d5faf2994410
• https://git.kernel.org/stable/c/64ef787bb1588475163069c2e62fdd8f6c27b1f6
• https://git.kernel.org/stable/c/809a5be62e92a444a3c3d7b9f438019d0b322f55
• https://git.kernel.org/stable/c/5c62852942667c613de0458fc797c5b8c36112b5
• https://git.kernel.org/stable/c/5c7cb94452901a93e90c2230632e2c12a681bc92