From: Eric Biggers <ebiggers@xxxxxxxxxx>
Add an ->s_master_keys keyring to 'struct super_block'. New fscrypt
ioctls will allow adding and removing encryption keys from this keyring.
This will enable solving multiple interrelated problems with how fscrypt
keys are provided and managed currently, including:
- Making the key status (which is currently per-process) match the
filesystem-level status of which encrypted files are "unlocked".
- Supporting a proper API to remove encryption keys, "locking" the
corresponding encrypted files.
- Caching an HMAC transform for each master key, allowing the use of
HKDF while still retaining good performance.
- Preventing denial of service via keyctl_invalidate().
Similar to the existing ->s_cop, the keyring is added to the VFS-level
superblock struct rather than separately to the ext4, f2fs, and ubifs
superblock structs so that it can be used by the shared code in
fs/crypto/. To minimize overhead, the keyring will only be allocated if
userspace actually adds a key; otherwise will stay NULL.
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
fs/super.c | 3 +++
include/linux/fs.h | 1 +
2 files changed, 4 insertions(+)
diff --git a/fs/super.c b/fs/super.c
index 48e25eba8465..7ca05dda905c 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -291,6 +291,9 @@ static void __put_super(struct super_block *s)
security_sb_free(s);
put_user_ns(s->s_user_ns);
kfree(s->s_subtype);
+#ifdef CONFIG_FS_ENCRYPTION
+ key_put(s->s_master_keys);
+#endif
call_rcu(&s->rcu, destroy_super_rcu);
}
}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index ba7889bb9ef6..70d929ac89f9 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1405,6 +1405,7 @@ struct super_block {
const struct xattr_handler **s_xattr;
#ifdef CONFIG_FS_ENCRYPTION
const struct fscrypt_operations *s_cop;
+ struct key *s_master_keys; /* master crypto keys in use */
#endif
struct hlist_bl_head s_roots; /* alternate root dentries for NFS */
struct list_head s_mounts; /* list of mounts; _not_ for fs use */
--
2.20.1
