diff mbox series

[v5,3/4] fbcon: Prevent that screen size is smaller than font size

Message ID 20220626085615.53728-4-deller@gmx.de (mailing list archive)
State Superseded
Headers show
Series fbcon: Fixes for screen resolution changes | expand

Commit Message

Helge Deller June 26, 2022, 8:56 a.m. UTC 
We need to prevent that users configure a screen size which is smaller than the
currently selected font size. Otherwise rendering chars on the screen will
access memory outside the graphics memory region.

This patch adds a new function fbcon_modechange_possible() which
implements this check and which later may be extended with other checks
if necessary.  The new function is called from the FBIOPUT_VSCREENINFO
ioctl handler in fbmem.c, which will return -EINVAL if userspace asked
for a too small screen size.

Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org # v5.4+
---
 drivers/video/fbdev/core/fbcon.c | 27 +++++++++++++++++++++++++++
 drivers/video/fbdev/core/fbmem.c |  4 +++-
 include/linux/fbcon.h            |  4 ++++
 3 files changed, 34 insertions(+), 1 deletion(-)

--
2.35.3

Comments

Daniel Vetter June 26, 2022, 9:58 a.m. UTC | #1 
On Sun, Jun 26, 2022 at 10:56:14AM +0200, Helge Deller wrote:
> We need to prevent that users configure a screen size which is smaller than the
> currently selected font size. Otherwise rendering chars on the screen will
> access memory outside the graphics memory region.
> 
> This patch adds a new function fbcon_modechange_possible() which
> implements this check and which later may be extended with other checks
> if necessary.  The new function is called from the FBIOPUT_VSCREENINFO
> ioctl handler in fbmem.c, which will return -EINVAL if userspace asked
> for a too small screen size.
> 
> Signed-off-by: Helge Deller <deller@gmx.de>
> Cc: stable@vger.kernel.org # v5.4+

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  drivers/video/fbdev/core/fbcon.c | 27 +++++++++++++++++++++++++++
>  drivers/video/fbdev/core/fbmem.c |  4 +++-
>  include/linux/fbcon.h            |  4 ++++
>  3 files changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> index e162d5e753e5..69c7261ac334 100644
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -2736,6 +2736,33 @@ void fbcon_update_vcs(struct fb_info *info, bool all)
>  }
>  EXPORT_SYMBOL(fbcon_update_vcs);
> 
> +/* let fbcon check if it supports a new screen resolution */
> +int fbcon_modechange_possible(struct fb_info *info, struct fb_var_screeninfo *var)
> +{
> +	struct fbcon_ops *ops = info->fbcon_par;
> +	struct vc_data *vc;
> +	int i;
> +
> +	WARN_CONSOLE_UNLOCKED();
> +
> +	if (!ops || ops->currcon < 0)
> +		return -EINVAL;
> +
> +	/* prevent setting a screen size which is smaller than font size */
> +	for (i = first_fb_vc; i <= last_fb_vc; i++) {
> +		vc = vc_cons[i].d;
> +		if (!vc || registered_fb[con2fb_map[i]] != info)
> +			continue;
> +
> +		if (vc->vc_font.width  > FBCON_SWAP(var->rotate, var->xres, var->yres) ||
> +		    vc->vc_font.height > FBCON_SWAP(var->rotate, var->yres, var->xres))
> +			return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(fbcon_modechange_possible);
> +
>  int fbcon_mode_deleted(struct fb_info *info,
>  		       struct fb_videomode *mode)
>  {
> diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
> index 5dfa4bbee642..b6e1d0f2b974 100644
> --- a/drivers/video/fbdev/core/fbmem.c
> +++ b/drivers/video/fbdev/core/fbmem.c
> @@ -1112,7 +1112,9 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
>  			return -EFAULT;
>  		console_lock();
>  		lock_fb_info(info);
> -		ret = fb_set_var(info, &var);
> +		ret = fbcon_modechange_possible(info, &var);
> +		if (!ret)
> +			ret = fb_set_var(info, &var);
>  		if (!ret)
>  			fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL);
>  		unlock_fb_info(info);
> diff --git a/include/linux/fbcon.h b/include/linux/fbcon.h
> index ff5596dd30f8..2382dec6d6ab 100644
> --- a/include/linux/fbcon.h
> +++ b/include/linux/fbcon.h
> @@ -15,6 +15,8 @@ void fbcon_new_modelist(struct fb_info *info);
>  void fbcon_get_requirement(struct fb_info *info,
>  			   struct fb_blit_caps *caps);
>  void fbcon_fb_blanked(struct fb_info *info, int blank);
> +int  fbcon_modechange_possible(struct fb_info *info,
> +			       struct fb_var_screeninfo *var);
>  void fbcon_update_vcs(struct fb_info *info, bool all);
>  void fbcon_remap_all(struct fb_info *info);
>  int fbcon_set_con2fb_map_ioctl(void __user *argp);
> @@ -33,6 +35,8 @@ static inline void fbcon_new_modelist(struct fb_info *info) {}
>  static inline void fbcon_get_requirement(struct fb_info *info,
>  					 struct fb_blit_caps *caps) {}
>  static inline void fbcon_fb_blanked(struct fb_info *info, int blank) {}
> +static inline int  fbcon_modechange_possible(struct fb_info *info,
> +				struct fb_var_screeninfo *var) { return 0; }
>  static inline void fbcon_update_vcs(struct fb_info *info, bool all) {}
>  static inline void fbcon_remap_all(struct fb_info *info) {}
>  static inline int fbcon_set_con2fb_map_ioctl(void __user *argp) { return 0; }
> --
> 2.35.3
>
diff mbox series

Patch

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index e162d5e753e5..69c7261ac334 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2736,6 +2736,33 @@  void fbcon_update_vcs(struct fb_info *info, bool all)
 }
 EXPORT_SYMBOL(fbcon_update_vcs);

+/* let fbcon check if it supports a new screen resolution */
+int fbcon_modechange_possible(struct fb_info *info, struct fb_var_screeninfo *var)
+{
+	struct fbcon_ops *ops = info->fbcon_par;
+	struct vc_data *vc;
+	int i;
+
+	WARN_CONSOLE_UNLOCKED();
+
+	if (!ops || ops->currcon < 0)
+		return -EINVAL;
+
+	/* prevent setting a screen size which is smaller than font size */
+	for (i = first_fb_vc; i <= last_fb_vc; i++) {
+		vc = vc_cons[i].d;
+		if (!vc || registered_fb[con2fb_map[i]] != info)
+			continue;
+
+		if (vc->vc_font.width  > FBCON_SWAP(var->rotate, var->xres, var->yres) ||
+		    vc->vc_font.height > FBCON_SWAP(var->rotate, var->yres, var->xres))
+			return -EINVAL;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL(fbcon_modechange_possible);
+
 int fbcon_mode_deleted(struct fb_info *info,
 		       struct fb_videomode *mode)
 {
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index 5dfa4bbee642..b6e1d0f2b974 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1112,7 +1112,9 @@  static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
 			return -EFAULT;
 		console_lock();
 		lock_fb_info(info);
-		ret = fb_set_var(info, &var);
+		ret = fbcon_modechange_possible(info, &var);
+		if (!ret)
+			ret = fb_set_var(info, &var);
 		if (!ret)
 			fbcon_update_vcs(info, var.activate & FB_ACTIVATE_ALL);
 		unlock_fb_info(info);
diff --git a/include/linux/fbcon.h b/include/linux/fbcon.h
index ff5596dd30f8..2382dec6d6ab 100644
--- a/include/linux/fbcon.h
+++ b/include/linux/fbcon.h
@@ -15,6 +15,8 @@  void fbcon_new_modelist(struct fb_info *info);
 void fbcon_get_requirement(struct fb_info *info,
 			   struct fb_blit_caps *caps);
 void fbcon_fb_blanked(struct fb_info *info, int blank);
+int  fbcon_modechange_possible(struct fb_info *info,
+			       struct fb_var_screeninfo *var);
 void fbcon_update_vcs(struct fb_info *info, bool all);
 void fbcon_remap_all(struct fb_info *info);
 int fbcon_set_con2fb_map_ioctl(void __user *argp);
@@ -33,6 +35,8 @@  static inline void fbcon_new_modelist(struct fb_info *info) {}
 static inline void fbcon_get_requirement(struct fb_info *info,
 					 struct fb_blit_caps *caps) {}
 static inline void fbcon_fb_blanked(struct fb_info *info, int blank) {}
+static inline int  fbcon_modechange_possible(struct fb_info *info,
+				struct fb_var_screeninfo *var) { return 0; }
 static inline void fbcon_update_vcs(struct fb_info *info, bool all) {}
 static inline void fbcon_remap_all(struct fb_info *info) {}
 static inline int fbcon_set_con2fb_map_ioctl(void __user *argp) { return 0; }