diff options
| author | Eric Biggers <ebiggers@google.com> | 2020-07-21 15:59:17 -0700 |
|---|---|---|
| committer | Eric Biggers <ebiggers@google.com> | 2020-07-21 16:02:13 -0700 |
| commit | 97c6327f7192d7312eabc033b26a41ad6816496c (patch) | |
| tree | 07b36406f882ba6ad91a800c832c8436417f9eb1 /fs/crypto/keysetup.c | |
| parent | bd0d97b7191e8f3573681fa854fdb04c1a970c1e (diff) | |
fscrypt: use smp_load_acquire() for fscrypt_prepared_key
Normally smp_store_release() or cmpxchg_release() is paired with
smp_load_acquire(). Sometimes smp_load_acquire() can be replaced with
the more lightweight READ_ONCE(). However, for this to be safe, all the
published memory must only be accessed in a way that involves the
pointer itself. This may not be the case if allocating the object also
involves initializing a static or global variable, for example.
fscrypt_prepared_key includes a pointer to a crypto_skcipher object,
which is internal to and is allocated by the crypto subsystem. By using
READ_ONCE() for it, we're relying on internal implementation details of
the crypto subsystem.
Remove this fragile assumption by using smp_load_acquire() instead.
(Note: I haven't seen any real-world problems here. This change is just
fixing the code to be guaranteed correct and less fragile.)
Fixes: 5fee36095cda ("fscrypt: add inline encryption support")
Cc: Satya Tangirala <satyat@google.com>
Link: https://lore.kernel.org/r/20200721225920.114347-3-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Diffstat (limited to 'fs/crypto/keysetup.c')
| -rw-r--r-- | fs/crypto/keysetup.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c index 22a94b18fe70..7f85fc645602 100644 --- a/fs/crypto/keysetup.c +++ b/fs/crypto/keysetup.c @@ -129,8 +129,10 @@ int fscrypt_prepare_key(struct fscrypt_prepared_key *prep_key, if (IS_ERR(tfm)) return PTR_ERR(tfm); /* - * Pairs with READ_ONCE() in fscrypt_is_key_prepared(). (Only matters - * for the per-mode keys, which are shared by multiple inodes.) + * Pairs with the smp_load_acquire() in fscrypt_is_key_prepared(). + * I.e., here we publish ->tfm with a RELEASE barrier so that + * concurrent tasks can ACQUIRE it. Note that this concurrency is only + * possible for per-mode keys, not for per-file keys. */ smp_store_release(&prep_key->tfm, tfm); return 0; |