Please sign in to comment.
fscrypt: remove broken support for detecting keyring key revocation
Filesystem encryption ostensibly supported revoking a keyring key that had been used to "unlock" encrypted files, causing those files to become "locked" again. This was, however, buggy for several reasons, the most severe of which was that when key revocation happened to be detected for an inode, its fscrypt_info was immediately freed, even while other threads could be using it for encryption or decryption concurrently. This could be exploited to crash the kernel or worse. This patch fixes the use-after-free by removing the code which detects the keyring key having been revoked, invalidated, or expired. Instead, an encrypted inode that is "unlocked" now simply remains unlocked until it is evicted from memory. Note that this is no worse than the case for block device-level encryption, e.g. dm-crypt, and it still remains possible for a privileged user to evict unused pages, inodes, and dentries by running 'sync; echo 3 > /proc/sys/vm/drop_caches', or by simply unmounting the filesystem. In fact, one of those actions was already needed anyway for key revocation to work even somewhat sanely. This change is not expected to break any applications. In the future I'd like to implement a real API for fscrypt key revocation that interacts sanely with ongoing filesystem operations --- waiting for existing operations to complete and blocking new operations, and invalidating and sanitizing key material and plaintext from the VFS caches. But this is a hard problem, and for now this bug must be fixed. This bug affected almost all versions of ext4, f2fs, and ubifs encryption, and it was potentially reachable in any kernel configured with encryption support (CONFIG_EXT4_ENCRYPTION=y, CONFIG_EXT4_FS_ENCRYPTION=y, CONFIG_F2FS_FS_ENCRYPTION=y, or CONFIG_UBIFS_FS_ENCRYPTION=y). Note that older kernels did not use the shared fs/crypto/ code, but due to the potential security implications of this bug, it may still be worthwhile to backport this fix to them. Fixes: b7236e2 ("ext4 crypto: reorganize how we store keys in the inode") Cc: firstname.lastname@example.org # v4.2+ Signed-off-by: Eric Biggers <email@example.com> Signed-off-by: Theodore Ts'o <firstname.lastname@example.org> Acked-by: Michael Halcrow <email@example.com>
- Loading branch information...
Showing with 11 additions and 57 deletions.