• Takashi Iwai's avatar
    ALSA: core: Fix card races between register and disconnect · 2a3f7221
    Takashi Iwai authored
    There is a small race window in the card disconnection code that
    allows the registration of another card with the very same card id.
    This leads to a warning in procfs creation as caught by syzkaller.
    
    The problem is that we delete snd_cards and snd_cards_lock entries at
    the very beginning of the disconnection procedure.  This makes the
    slot available to be assigned for another card object while the
    disconnection procedure is being processed.  Then it becomes possible
    to issue a procfs registration with the existing file name although we
    check the conflict beforehand.
    
    The fix is simply to move the snd_cards and snd_cards_lock clearances
    at the end of the disconnection procedure.  The references to these
    entries are merely either from the global proc files like
    /proc/asound/cards or from the card registration / disconnection, so
    it should be fine to shift at the very end.
    
    Reported-by: syzbot+48df349490c36f9f54ab@syzkaller.appspotmail.com
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
    2a3f7221
init.c 26 KB