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fscrypt: simplify master key locking

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commit 4a4b8721f1a5e4b01e45b3153c68d5a1014b25de upstream.

The stated reasons for separating fscrypt_master_key::mk_secret_sem from
the standard semaphore contained in every 'struct key' no longer apply.

First, due to commit a992b20cd4 ("fscrypt: add
fscrypt_prepare_new_inode() and fscrypt_set_context()"),
fscrypt_get_encryption_info() is no longer called from within a
filesystem transaction.

Second, due to commit d3ec10aa95 ("KEYS: Don't write out to userspace
while holding key semaphore"), the semaphore for the "keyring" key type
no longer ranks above page faults.

That leaves performance as the only possible reason to keep the separate
mk_secret_sem.  Specifically, having mk_secret_sem reduces the
contention between setup_file_encryption_key() and
FS_IOC_{ADD,REMOVE}_ENCRYPTION_KEY.  However, these ioctls aren't
executed often, so this doesn't seem to be worth the extra complexity.

Therefore, simplify the locking design by just using key->sem instead of
mk_secret_sem.

Link: https://lore.kernel.org/r/20201117032626.320275-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Eric Biggers
2022-11-04 16:37:58 -07:00
committed by Greg Kroah-Hartman
parent 54c13d3520
commit 092401142b
4 changed files with 21 additions and 34 deletions
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8
fs/crypto/hooks.c
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@@ -139,6 +139,7 @@ int fscrypt_prepare_setflags(struct inode *inode,
unsigned int oldflags, unsigned int flags)
{
struct fscrypt_info *ci;
struct key *key;
struct fscrypt_master_key *mk;
int err;
@@ -154,13 +155,14 @@ int fscrypt_prepare_setflags(struct inode *inode,
ci = inode->i_crypt_info;
if (ci->ci_policy.version != FSCRYPT_POLICY_V2)
return -EINVAL;
mk = ci->ci_master_key->payload.data[0];
down_read(&mk->mk_secret_sem);
key = ci->ci_master_key;
mk = key->payload.data[0];
down_read(&key->sem);
if (is_master_key_secret_present(&mk->mk_secret))
err = fscrypt_derive_dirhash_key(ci, mk);
else
err = -ENOKEY;
up_read(&mk->mk_secret_sem);
up_read(&key->sem);
return err;
}
return 0;