From: Mushahid Hussain <mushi.shar@xxxxxxxxx>
commit 0fc801f8018000c8e64a275a20cb1da7c54e46df upstream.
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.
Fixes: 2610df41489f ("staging: speakup: Add pause command used on switching to graphical mode")
Cc: stable <stable@xxxxxxxxxx>
Signed-off-by: Mushahid Hussain <mushi.shar@xxxxxxxxx>
Signed-off-by: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20221010165720.397042-1-mushi.shar@xxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/accessibility/speakup/main.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/accessibility/speakup/main.c
+++ b/drivers/accessibility/speakup/main.c
@@ -1778,7 +1778,7 @@ static void speakup_con_update(struct 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 */
