Re: [PATCH] Speakup: fix a segfault caused by switching consoles

[Greg KH <gregkh@linuxfoundation.org>]

On Mon, Oct 10, 2022 at 09:57:20PM +0500, Mushahid Hussain wrote:
> This patch fixes a segfault by adding a null check on synth in
> speakup_con_update(). The segfault can be reproduced as follows:
> 
> 	- Login into a text console
> 
> 	- Load speakup and speakup_soft modules
> 
> 	- Remove speakup_soft
> 
> 	- Switch to a graphics console
> 
> This is caused by lack of a null check on `synth` in
> speakup_con_update().
> 
> Here's the sequence that causes the segfault:
> 
> 	- When we remove the speakup_soft, synth_release() sets the synth
> 	  to null.
> 
> 	- After that, when we change the virtual console to graphics
> 	  console, vt_notifier_call() is fired, which then calls
> 	  speakup_con_update().
> 
> 	- Inside speakup_con_update() there's no null check on synth,
> 	  so it calls synth_printf().
> 
> 	- Inside synth_printf(), synth_buffer_add() and synth_start(),
> 	  both access synth, when it is null and causing a segfault.
> 
> Therefore adding a null check on synth solves the issue.
> 
> Signed-off-by: Mushahid Hussain <mushi.shar@gmail.com>
> Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
> ---
>  drivers/accessibility/speakup/main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

What commit id does this fix?  Should it go to stable kernels?

thanks,

greg k-h