4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Helge Deller <deller@xxxxxx>
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@xxxxxx>
Reviewed-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v5.4+
Signed-off-by: Hugo SIMELIERE <hsimeliere.opensource@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/video/fbdev/core/fbcon.c | 28 ++++++++++++++++++++++++++++
drivers/video/fbdev/core/fbmem.c | 9 ++++++---
include/linux/fbcon.h | 4 ++++
3 files changed, 38 insertions(+), 3 deletions(-)
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2734,6 +2734,34 @@ static void fbcon_set_all_vcs(struct fb_
fbcon_modechanged(info);
}
+/* 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);
+
static int fbcon_mode_deleted(struct fb_info *info,
struct fb_videomode *mode)
{
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1121,9 +1121,12 @@ static long do_fb_ioctl(struct fb_info *
console_unlock();
return -ENODEV;
}
- info->flags |= FBINFO_MISC_USEREVENT;
- ret = fb_set_var(info, &var);
- info->flags &= ~FBINFO_MISC_USEREVENT;
+ ret = fbcon_modechange_possible(info, &var);
+ if (!ret) {
+ info->flags |= FBINFO_MISC_USEREVENT;
+ ret = fb_set_var(info, &var);
+ info->flags &= ~FBINFO_MISC_USEREVENT;
+ }
unlock_fb_info(info);
console_unlock();
if (!ret && copy_to_user(argp, &var, sizeof(var)))
--- a/include/linux/fbcon.h
+++ b/include/linux/fbcon.h
@@ -4,9 +4,13 @@
#ifdef CONFIG_FRAMEBUFFER_CONSOLE
void __init fb_console_init(void);
void __exit fb_console_exit(void);
+int fbcon_modechange_possible(struct fb_info *info,
+ struct fb_var_screeninfo *var);
#else
static inline void fb_console_init(void) {}
static inline void fb_console_exit(void) {}
+static inline int fbcon_modechange_possible(struct fb_info *info,
+ struct fb_var_screeninfo *var) { return 0; }
#endif
#endif /* _LINUX_FBCON_H */
