fsverity: RCU-delay the freeing of struct fsverity_info

Overview

In the Linux kernel, the following vulnerability has been resolved:

fsverity: RCU-delay the freeing of struct fsverity_info

__fsverity_get_info() calls rhashtable_lookup_fast(), which just uses rcu_read_lock() and doesn't directly synchronize with fsverity_remove_info().

For the same inode this isn't a problem: its fsverity_info is removed only at inode eviction time or upon failure to enable verity, when the inode no longer needs its fsverity_info and it will no longer be accessed via that inode.

However, this is broken and can cause a use-after-free for concurrent __fsverity_get_info() for different inodes. Those rely on following fsverity_info::rhash_head in the rhashtable under rcu_read_lock() only. They also use fsverity_info::inode to do the key comparison.

Fix this by RCU-delaying the freeing of 'struct fsverity_info' after it's been removed from the rhashtable.

Affected

• Linux >= f77f281b61183a5c0b87e6a4d101c70bd32c1c79 < fa84f091a8e7fc46fd29834496fab9739dd4c8dc
• Linux >= f77f281b61183a5c0b87e6a4d101c70bd32c1c79 < e58c3805ed325fe2d4ae2dd467c0486cc860b733
• Linux 7.0

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.