diff options
| author | Eric Biggers <ebiggers@google.com> | 2020-07-21 15:59:20 -0700 |
|---|---|---|
| committer | Eric Biggers <ebiggers@google.com> | 2020-07-21 16:02:41 -0700 |
| commit | f3db0bed458314a835ccef5ccb130270c5b2cf04 (patch) | |
| tree | 0a9b6eacb0dea29a4a18bf24ae56e29a67d3de08 /include/linux/fsverity.h | |
| parent | ba47d845d715a010f7b51f6f89bae32845e6acb7 (diff) | |
fs-verity: use smp_load_acquire() for ->i_verity_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.
fsverity_info::tree_params.hash_alg->tfm is a crypto_ahash object that's
internal to and is allocated by the crypto subsystem. So by using
READ_ONCE() for ->i_verity_info, we're relying on internal
implementation details of the crypto subsystem.
Remove this fragile assumption by using smp_load_acquire() instead.
Also fix the cmpxchg logic to correctly execute an ACQUIRE barrier when
losing the cmpxchg race, since cmpxchg doesn't guarantee a memory
barrier on failure.
(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: fd2d1acfcadf ("fs-verity: add the hook for file ->open()")
Link: https://lore.kernel.org/r/20200721225920.114347-6-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@google.com>
Diffstat (limited to 'include/linux/fsverity.h')
| -rw-r--r-- | include/linux/fsverity.h | 9 |
1 files changed, 7 insertions, 2 deletions
diff --git a/include/linux/fsverity.h b/include/linux/fsverity.h index 78201a6d35f6..c1144a450392 100644 --- a/include/linux/fsverity.h +++ b/include/linux/fsverity.h @@ -115,8 +115,13 @@ struct fsverity_operations { static inline struct fsverity_info *fsverity_get_info(const struct inode *inode) { - /* pairs with the cmpxchg() in fsverity_set_info() */ - return READ_ONCE(inode->i_verity_info); + /* + * Pairs with the cmpxchg_release() in fsverity_set_info(). + * I.e., another task may publish ->i_verity_info concurrently, + * executing a RELEASE barrier. We need to use smp_load_acquire() here + * to safely ACQUIRE the memory the other task published. + */ + return smp_load_acquire(&inode->i_verity_info); } /* enable.c */ |