From: Helge Deller deller@gmx.de
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 --- drivers/video/fbdev/core/fbcon.c | 28 ++++++++++++++++++++++++++++ drivers/video/fbdev/core/fbmem.c | 4 +++- include/linux/fbcon.h | 4 ++++ 3 files changed, 35 insertions(+), 1 deletion(-)
--- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c @@ -2761,6 +2761,34 @@ void fbcon_update_vcs(struct fb_info *in } 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) { --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1114,7 +1114,9 @@ static long do_fb_ioctl(struct fb_info * 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); --- a/include/linux/fbcon.h +++ b/include/linux/fbcon.h @@ -15,6 +15,8 @@ void fbcon_new_modelist(struct fb_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(st 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; }