• Eric Biggers's avatar
    fscrypt: use smp_load_acquire() for fscrypt_prepared_key · 97c6327f
    Eric Biggers authored
    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: 5fee3609 ("fscrypt: add inline encryption support")
    Cc: Satya Tangirala <satyat@google.com>
    Link: https://lore.kernel.org/r/20200721225920.114347-3-ebiggers@kernel.orgSigned-off-by: default avatarEric Biggers <ebiggers@google.com>
    97c6327f
inline_crypt.c 11.1 KB