• Eric Biggers's avatar
    fscrypt: use smp_load_acquire() for ->i_crypt_info · ab673b98
    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_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: e37a784d ("fscrypt: use READ_ONCE() to access ->i_crypt_info")
    Link: https://lore.kernel.org/r/20200721225920.114347-5-ebiggers@kernel.orgSigned-off-by: default avatarEric Biggers <ebiggers@google.com>
    ab673b98
policy.c 23.4 KB