d8a2dca040
commit e1a7bfe3807974e66f971f2589d4e0197ec0fced upstream. The procedure for adding a user control element has some window opened for race against the concurrent removal of a user element. This was caught by syzkaller, hitting a KASAN use-after-free error. This patch addresses the bug by wrapping the whole procedure to add a user control element with the card->controls_rwsem, instead of only around the increment of card->user_ctl_count. This required a slight code refactoring, too. The function snd_ctl_add() is split to two parts: a core function to add the control element and a part calling it. The former is called from the function for adding a user control element inside the controls_rwsem. One change to be noted is that snd_ctl_notify() for adding a control element gets called inside the controls_rwsem as well while it was called outside the rwsem. But this should be OK, as snd_ctl_notify() takes another (finer) rwlock instead of rwsem, and the call of snd_ctl_notify() inside rwsem is already done in another code path. Reported-by: syzbot+dc09047bce3820621ba2@syzkaller.appspotmail.com Cc: <stable@vger.kernel.org> Signed-off-by: Takashi Iwai <tiwai@suse.de> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.