CVE-2022-49899: In the Linux kernel, the following vulnerability has been resolved:  fscrypt: stop using keyrings subsystem for fscrypt_master_key  The approach of fs/crypto/ internally managing the fscrypt_master_key structs as the payloads of "struct key" objects contained in a "struct key" keyring has outlived its usefulness.  The original idea was to simplify the code by reusing code from the keyrings subsystem. However, several issues have arisen that can't easily be resolved:  - When a master key struct is destroyed, blk_crypto_evict_key() must be   called on any per-mode keys embedded in it.  (This started being the   case when inline encryption support was added.)  Yet, the keyrings   subsystem can arbitrarily delay the destruction of keys, even past the   time the filesystem was unmounted.  Therefore, currently there is no   easy way to call blk_crypto_evict_key() when a master key is   destroyed.  Currently, this is worked around by holding an extra   reference to the filesystem's request_queue(s).  But it was overlooked   that the request_queue reference is *not* guaranteed to pin the   corresponding blk_crypto_profile too; for device-mapper devices that   support inline crypto, it doesn't.  This can cause a use-after-free.  - When the last inode that was using an incompletely-removed master key   is evicted, the master key removal is completed by removing the key   struct from the keyring.  Currently this is done via key_invalidate().   Yet, key_invalidate() takes the key semaphore.  This can deadlock when   called from the shrinker, since in fscrypt_ioctl_add_key(), memory is   allocated with GFP_KERNEL under the same semaphore.  - More generally, the fact that the keyrings subsystem can arbitrarily   delay the destruction of keys (via garbage collection delay, or via   random processes getting temporary key references) is undesirable, as   it means we can't strictly guarantee that all secrets are ever wiped.  - Doing the master key lookups via the keyrings subsystem results in the   key_permission LSM hook being called.  fscrypt doesn't want this, as   all access control for encrypted files is designed to happen via the   files themselves, like any other files.  The workaround which SELinux   users are using is to change their SELinux policy to grant key search   access to all domains.  This works, but it is an odd extra step that   shouldn't really have to be done.  The fix for all these issues is to change the implementation to what I should have done originally: don't use the keyrings subsystem to keep track of the filesystem's fscrypt_master_key structs.  Instead, just store them in a regular kernel data structure, and rework the reference counting, locking, and lifetime accordingly.  Retain support for RCU-mode key lookups by using a hash table.  Replace fscrypt_sb_free() with fscrypt_sb_delete(), which releases the keys synchronously and runs a bit earlier during unmount, so that block devices are still available.  A side effect of this patch is that neither the master keys themselves nor the filesystem keyrings will be listed in /proc/keys anymore. ("Master key users" and the master key users keyrings will still be listed.)  However, this was mostly an implementation detail, and it was intended just for debugging purposes.  I don't know of anyone using it.  This patch does *not* change how "master key users" (->mk_users) works; that still uses the keyrings subsystem.  That is still needed for key quotas, and changing that isn't necessary to solve the issues listed above.  If we decide to change that too, it would be a separate patch.  I've marked this as fixing the original commit that added the fscrypt keyring, but as noted above the most important issue that this patch fixes wasn't introduced until the addition of inline encryption support.