Re: [PATCH 6.8.y-and-older] ALSA: timer: Set lower bound of start tick time

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Mon, May 27, 2024 at 08:23:59AM +0200, Takashi Iwai wrote:
> commit 4a63bd179fa8d3fcc44a0d9d71d941ddd62f0c4e upstream.
> 
> Currently ALSA timer doesn't have the lower limit of the start tick
> time, and it allows a very small size, e.g. 1 tick with 1ns resolution
> for hrtimer.  Such a situation may lead to an unexpected RCU stall,
> where  the callback repeatedly queuing the expire update, as reported
> by fuzzer.
> 
> This patch introduces a sanity check of the timer start tick time, so
> that the system returns an error when a too small start size is set.
> As of this patch, the lower limit is hard-coded to 100us, which is
> small enough but can still work somehow.
> 
> [ backport note: the error handling is changed, as the original commit
>   is based on the recent cleanup with guard() in commit beb45974dd49
>   -- tiwai ]
> 
> Reported-by: syzbot+43120c2af6ca2938cc38@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/r/000000000000fa00a1061740ab6d@google.com
> Cc: <stable@vger.kernel.org>
> Link: https://lore.kernel.org/r/20240514182745.4015-1-tiwai@suse.de
> Signed-off-by: Takashi Iwai <tiwai@suse.de>
> ---
> 
> Greg, this is an alternative fix to the original cherry-pick; apply
> to 6.8.y and older stable kernels.  Thanks!

Now queued up, thanks!

greg k-h