• Wenwen Wang's avatar
    ALSA: control: fix a redundant-copy issue · 3f12888d
    Wenwen Wang authored
    In snd_ctl_elem_add_compat(), the fields of the struct 'data' need to be
    copied from the corresponding fields of the struct 'data32' in userspace.
    This is achieved by invoking copy_from_user() and get_user() functions. The
    problem here is that the 'type' field is copied twice. One is by
    copy_from_user() and one is by get_user(). Given that the 'type' field is
    not used between the two copies, the second copy is *completely* redundant
    and should be removed for better performance and cleanup. Also, these two
    copies can cause inconsistent data: as the struct 'data32' resides in
    userspace and a malicious userspace process can race to change the 'type'
    field between the two copies to cause inconsistent data. Depending on how
    the data is used in the future, such an inconsistency may cause potential
    security risks.
    
    For above reasons, we should take out the second copy.
    Signed-off-by: default avatarWenwen Wang <wang6495@umn.edu>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
    3f12888d
control_compat.c 13 KB