From e37a784d8b6a1e726de5ddc7b4809c086a08db09 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Thu, 11 Apr 2019 14:32:15 -0700 Subject: fscrypt: use READ_ONCE() to access ->i_crypt_info ->i_crypt_info starts out NULL and may later be locklessly set to a non-NULL value by the cmpxchg() in fscrypt_get_encryption_info(). But ->i_crypt_info is used directly, which technically is incorrect. It's a data race, and it doesn't include the data dependency barrier needed to safely dereference the pointer on at least one architecture. Fix this by using READ_ONCE() instead. Note: we don't need to use smp_load_acquire(), since dereferencing the pointer only requires a data dependency barrier, which is already included in READ_ONCE(). We also don't need READ_ONCE() in places where ->i_crypt_info is unconditionally dereferenced, since it must have already been checked. Also downgrade the cmpxchg() to cmpxchg_release(), since RELEASE semantics are sufficient on the write side. Signed-off-by: Eric Biggers Signed-off-by: Theodore Ts'o --- include/linux/fscrypt.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'include/linux/fscrypt.h') diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h index 6cf8a34523ff..ec8ab7108599 100644 --- a/include/linux/fscrypt.h +++ b/include/linux/fscrypt.h @@ -79,7 +79,8 @@ struct fscrypt_ctx { static inline bool fscrypt_has_encryption_key(const struct inode *inode) { - return (inode->i_crypt_info != NULL); + /* pairs with cmpxchg_release() in fscrypt_get_encryption_info() */ + return READ_ONCE(inode->i_crypt_info) != NULL; } static inline bool fscrypt_dummy_context_enabled(struct inode *inode) -- cgit v1.2.3