On Wed, Jan 31, 2018 at 06:06:09PM +0000, Ben Hutchings wrote:
From: Takashi Iwai tiwai@suse.de
commit b3defb791b26ea0683a93a4f49c77ec45ec96f10 upstream.
The ALSA sequencer ioctls have no protection against racy calls while the concurrent operations may lead to interfere with each other. As reported recently, for example, the concurrent calls of setting client pool with a combination of write calls may lead to either the unkillable dead-lock or UAF.
As a slightly big hammer solution, this patch introduces the mutex to make each ioctl exclusive. Although this may reduce performance via parallel ioctl calls, usually it's not demanded for sequencer usages, hence it should be negligible.
Reported-by: Luo Quan a4651386@163.com Reviewed-by: Kees Cook keescook@chromium.org Reviewed-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Takashi Iwai tiwai@suse.de [bwh: Backported to 4.4: ioctl dispatch is done from snd_seq_do_ioctl(); take the mutex and add ret variable there.]
Thanks for the backport, now applied.
greg k-h