4.19-stable review patch. If anyone has any objections, please let me know.
------------------
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: Hugo SIMELIERE hsimeliere.opensource@witekio.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- 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 */