2022-10-10 17:00:29

by SikkiLadho

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

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 <[email protected]>
Signed-off-by: Samuel Thibault <[email protected]>
---
drivers/accessibility/speakup/main.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/accessibility/speakup/main.c b/drivers/accessibility/speakup/main.c
index f52265293482..73db0cb44fc7 100644
--- a/drivers/accessibility/speakup/main.c
+++ b/drivers/accessibility/speakup/main.c
@@ -1778,7 +1778,7 @@ static void speakup_con_update(struct vc_data *vc)
{
unsigned long flags;

- if (!speakup_console[vc->vc_num] || spk_parked)
+ if (!speakup_console[vc->vc_num] || spk_parked || !synth)
return;
if (!spin_trylock_irqsave(&speakup_info.spinlock, flags))
/* Speakup output, discard */
--
2.38.0

2022-10-10 17:42:40

by Greg Kroah-Hartman

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

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 <[email protected]>
> Signed-off-by: Samuel Thibault <[email protected]>
> ---
> 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

2022-10-10 18:05:01

by Samuel Thibault

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

Hello,

Greg KH, le lun. 10 oct. 2022 19:02:46 +0200, a ecrit:
> 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 <[email protected]>
> > Signed-off-by: Samuel Thibault <[email protected]>
> > ---
> > drivers/accessibility/speakup/main.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
>
> What commit id does this fix?

It is there since 2610df41489f548e235171b86895d4b49e6acb1f
("staging: speakup: Add pause command used on switching to graphical
mode")

> Should it go to stable kernels?

Yes, please.

Mushahid, you can see in Documentation/process/submitting-patches.rst
how to encode this in the patch submission.

Samuel