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fbcon: Prevent that screen size is smaller than font size

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commit e64242caef18b4a5840b0e7a9bff37abd4f4f933 upstream.

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>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: stable@vger.kernel.org # v5.4+
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Helge Deller 2022-06-25 13:00:34 +02:00 committed by Greg Kroah-Hartman
parent 4f34f380f9
commit af93e82197
3 changed files with 35 additions and 1 deletions
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28
drivers/video/fbdev/core/fbcon.c
View File

@ -2761,6 +2761,34 @@ 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;
unsigned int i;
WARN_CONSOLE_UNLOCKED();
if (!ops)
return 0;
/* 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 || vc->vc_mode != KD_TEXT ||
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_GPL(fbcon_modechange_possible);
int fbcon_mode_deleted(struct fb_info *info,
struct fb_videomode *mode)
{

4
drivers/video/fbdev/core/fbmem.c
View File

@ -1114,7 +1114,9 @@ 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);

4
include/linux/fbcon.h
View File

@ -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; }