This issue happens when a userspace program does an ioctl
FBIOPUT_VSCREENINFO passing the fb_var_screeninfo struct
containing only the fields xres, yres, and bits_per_pixel
with values.
If this struct is the same as the previous ioctl, the
vc_resize() detects it and doesn't call the resize_screen(),
leaving the fb_var_screeninfo incomplete. And this leads to
the updatescrollmode() calculates a wrong value to
fbcon_display->vrows, which makes the real_y() return a
wrong value of y, and that value, eventually, causes
the imageblit to access an out-of-bound address value.
To solve this issue I made the resize_screen() be called
even if the screen does not need any resizing, so it will
"fix and fill" the fb_var_screeninfo independently.
Reported-and-tested-by: [email protected]
Signed-off-by: Igor Matheus Andrade Torrente <[email protected]>
---
v2: It Tries to avoid the problem found by Greg in the previous
patch.
v3: Add a big comment explaining why this is being done the way
it is.
---
drivers/tty/vt/vt.c | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index fa1548d4f94b..a0207525a945 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1220,7 +1220,20 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc,
new_screen_size = new_row_size * new_rows;
if (new_cols == vc->vc_cols && new_rows == vc->vc_rows)
- return 0;
+ /* This function is being called here to cover the case
+ * where the userspace calls the FBIOPUT_VSCREENINFO twice,
+ * passing the same fb_var_screeninfo containing only the
+ * fields xres, yres, and bits_per_pixel with yeird(but valid)
+ * values.
+ * In the second call, the struct fb_var_screeninfo isn't
+ * being modified by the underlying driver because of the
+ * if above, and this eventually causes out-of-bound
+ * access by the imageblit function.
+ * To give the correct values to the struct and to not have
+ * to deal with possible erros from the code bellow, we call
+ * the resize_screen here as well.
+ */
+ return resize_screen(vc, new_cols, new_rows, user);
if (new_screen_size > KMALLOC_MAX_SIZE || !new_screen_size)
return -EINVAL;
--
2.20.1
On Thu, Jun 17, 2021 at 07:37:20PM -0300, Igor Matheus Andrade Torrente wrote:
> This issue happens when a userspace program does an ioctl
> FBIOPUT_VSCREENINFO passing the fb_var_screeninfo struct
> containing only the fields xres, yres, and bits_per_pixel
> with values.
>
> If this struct is the same as the previous ioctl, the
> vc_resize() detects it and doesn't call the resize_screen(),
> leaving the fb_var_screeninfo incomplete. And this leads to
> the updatescrollmode() calculates a wrong value to
> fbcon_display->vrows, which makes the real_y() return a
> wrong value of y, and that value, eventually, causes
> the imageblit to access an out-of-bound address value.
>
> To solve this issue I made the resize_screen() be called
> even if the screen does not need any resizing, so it will
> "fix and fill" the fb_var_screeninfo independently.
>
> Reported-and-tested-by: [email protected]
> Signed-off-by: Igor Matheus Andrade Torrente <[email protected]>
> ---
> v2: It Tries to avoid the problem found by Greg in the previous
> patch.
>
> v3: Add a big comment explaining why this is being done the way
> it is.
> ---
> drivers/tty/vt/vt.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> index fa1548d4f94b..a0207525a945 100644
> --- a/drivers/tty/vt/vt.c
> +++ b/drivers/tty/vt/vt.c
> @@ -1220,7 +1220,20 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc,
> new_screen_size = new_row_size * new_rows;
>
> if (new_cols == vc->vc_cols && new_rows == vc->vc_rows)
> - return 0;
> + /* This function is being called here to cover the case
Please do not use networking style comments, use normal ones:
/*
* This function...
> + * where the userspace calls the FBIOPUT_VSCREENINFO twice,
> + * passing the same fb_var_screeninfo containing only the
> + * fields xres, yres, and bits_per_pixel with yeird(but valid)
"yeird"?
And put a space after that word please.
thanks,
greg k-h