diff options
| author | Eric Biggers <ebiggers@google.com> | 2020-07-21 15:59:19 -0700 |
|---|---|---|
| committer | Eric Biggers <ebiggers@google.com> | 2020-07-21 16:02:13 -0700 |
| commit | ab673b987488c4fab7a0bc4824a48211f9d910e3 (patch) | |
| tree | 16ec1d6324aa8c0fe60f3d5f45f35b65de43f2ae /fs/crypto/keysetup.c | |
| parent | 777afe4e68d7ac37711d36098bea65650ec305a0 (diff) | |
fscrypt: use smp_load_acquire() for ->i_crypt_info
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_info includes various sub-objects which are internal to and are
allocated by other kernel subsystems such as keyrings and crypto. So by
using READ_ONCE() for ->i_crypt_info, we're relying on internal
implementation details of these other kernel subsystems.
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: e37a784d8b6a ("fscrypt: use READ_ONCE() to access ->i_crypt_info")
Link: https://lore.kernel.org/r/20200721225920.114347-5-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 | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c index 7f85fc645602..fea6226afc2b 100644 --- a/fs/crypto/keysetup.c +++ b/fs/crypto/keysetup.c @@ -518,7 +518,17 @@ int fscrypt_get_encryption_info(struct inode *inode) if (res) goto out; + /* + * Multiple tasks may race to set ->i_crypt_info, so use + * cmpxchg_release(). This pairs with the smp_load_acquire() in + * fscrypt_get_info(). I.e., here we publish ->i_crypt_info with a + * RELEASE barrier so that other tasks can ACQUIRE it. + */ if (cmpxchg_release(&inode->i_crypt_info, NULL, crypt_info) == NULL) { + /* + * We won the race and set ->i_crypt_info to our crypt_info. + * Now link it into the master key's inode list. + */ if (master_key) { struct fscrypt_master_key *mk = master_key->payload.data[0]; @@ -589,7 +599,7 @@ EXPORT_SYMBOL(fscrypt_free_inode); */ int fscrypt_drop_inode(struct inode *inode) { - const struct fscrypt_info *ci = READ_ONCE(inode->i_crypt_info); + const struct fscrypt_info *ci = fscrypt_get_info(inode); const struct fscrypt_master_key *mk; /* |