mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2025-01-12 16:19:53 +00:00
7206998f57
When a codec is unbound dynamically via sysfs while its stream is in
use, we may face a potential deadlock at the proc remove or a UAF.
This happens since the hda_pcm is managed by a linked list, as it
handles the hda_pcm object release via kref.
When a PCM is opened at the unbinding time, the release of hda_pcm
gets delayed and it ends up with the close of the PCM stream releasing
the associated hda_pcm object of its own. The hda_pcm destructor
contains the PCM device release that includes the removal of procfs
entries. And, this removal has the sync of the close of all in-use
files -- which would never finish because it's called from the PCM
file descriptor itself, i.e. it's trying to shoot its foot.
For addressing the deadlock above, this patch changes the way to
manage and release the hda_pcm object. The kref of hda_pcm is
dropped, and instead a simple refcount is introduced in hda_codec for
keeping the track of the active PCM streams, and at each PCM open and
close, this refcount is adjusted accordingly. At unbinding, the
driver calls snd_device_disconnect() for each PCM stream, then
synchronizes with the refcount finish, and finally releases the object
resources.
Fixes: bbbc7e8502c9 ("ALSA: hda - Allocate hda_pcm objects dynamically")
Link: https://lore.kernel.org/r/20211116072459.18930-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.