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[7/7] video: fbdev: s3fb: Error out if 'pixclock' equals zero

Message ID 20220404084723.79089-8-zheyuma97@gmail.com (mailing list archive)
State Accepted, archived
Headers show
Series Fix divide errors in fbdev drivers | expand

Commit Message

Zheyu Ma April 4, 2022, 8:47 a.m. UTC
The userspace program could pass any values to the driver through
ioctl() interface. If the driver doesn't check the value of 'pixclock',
it may cause divide error.

Fix this by checking whether 'pixclock' is zero in s3fb_check_var().

The following log reveals it:

[  511.141561] divide error: 0000 [#1] PREEMPT SMP KASAN PTI
[  511.141607] RIP: 0010:s3fb_check_var+0x3f3/0x530
[  511.141693] Call Trace:
[  511.141695]  <TASK>
[  511.141716]  fb_set_var+0x367/0xeb0
[  511.141815]  do_fb_ioctl+0x234/0x670
[  511.141876]  fb_ioctl+0xdd/0x130
[  511.141888]  do_syscall_64+0x3b/0x90

Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
---
 drivers/video/fbdev/s3fb.c | 3 +++
 1 file changed, 3 insertions(+)

Comments

Geert Uytterhoeven April 4, 2022, 3:52 p.m. UTC | #1
On Mon, Apr 4, 2022 at 3:50 PM Zheyu Ma <zheyuma97@gmail.com> wrote:
> The userspace program could pass any values to the driver through
> ioctl() interface. If the driver doesn't check the value of 'pixclock',
> it may cause divide error.
>
> Fix this by checking whether 'pixclock' is zero in s3fb_check_var().
>
> The following log reveals it:
>
> [  511.141561] divide error: 0000 [#1] PREEMPT SMP KASAN PTI
> [  511.141607] RIP: 0010:s3fb_check_var+0x3f3/0x530
> [  511.141693] Call Trace:
> [  511.141695]  <TASK>
> [  511.141716]  fb_set_var+0x367/0xeb0
> [  511.141815]  do_fb_ioctl+0x234/0x670
> [  511.141876]  fb_ioctl+0xdd/0x130
> [  511.141888]  do_syscall_64+0x3b/0x90
>
> Signed-off-by: Zheyu Ma <zheyuma97@gmail.com>
> ---
>  drivers/video/fbdev/s3fb.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/video/fbdev/s3fb.c b/drivers/video/fbdev/s3fb.c
> index 5c74253e7b2c..b93c8eb02336 100644
> --- a/drivers/video/fbdev/s3fb.c
> +++ b/drivers/video/fbdev/s3fb.c
> @@ -549,6 +549,9 @@ static int s3fb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
>         int rv, mem, step;
>         u16 m, n, r;
>
> +       if (!var->pixclock)
> +               return -EINVAL;
> +

When passed an invalid value, .check_var() is supposed to
round up the invalid value to a valid value, if possible.

>         /* Find appropriate format */
>         rv = svga_match_format (s3fb_formats, var, NULL);

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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Patch

diff --git a/drivers/video/fbdev/s3fb.c b/drivers/video/fbdev/s3fb.c
index 5c74253e7b2c..b93c8eb02336 100644
--- a/drivers/video/fbdev/s3fb.c
+++ b/drivers/video/fbdev/s3fb.c
@@ -549,6 +549,9 @@  static int s3fb_check_var(struct fb_var_screeninfo *var, struct fb_info *info)
 	int rv, mem, step;
 	u16 m, n, r;
 
+	if (!var->pixclock)
+		return -EINVAL;
+
 	/* Find appropriate format */
 	rv = svga_match_format (s3fb_formats, var, NULL);