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 may be extended with other checks later if necessary. The
new function will be called from the FBIOPUT_VSCREENINFO ioctl handler in
fbmem.c, which will then return -EINVAL to the user if the new screen size is
too small.
Signed-off-by: Helge Deller <deller@xxxxxx>
Cc: stable@xxxxxxxxxxxxxxx # v5.4+
---
drivers/video/fbdev/core/fbcon.c | 26 ++++++++++++++++++++++++++
include/linux/fbcon.h | 4 ++++
2 files changed, 30 insertions(+)
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index e162d5e753e5..e4cc4841ed7f 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2736,6 +2736,32 @@ 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;
+
+ 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 || vc->vc_mode != KD_TEXT ||
+ fbcon_info_from_console(i) != info)
+ continue;
+
+ if (FBCON_SWAP(var->rotate, var->xres, var->yres) < vc->vc_font.width ||
+ FBCON_SWAP(var->rotate, var->yres, var->xres) < vc->vc_font.height)
+ return -EINVAL;
+ }
+
+ return 0;
+}
+EXPORT_SYMBOL(fbcon_modechange_possible);
+
int fbcon_mode_deleted(struct fb_info *info,
struct fb_videomode *mode)
{
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
