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+ Link: https://lore.kernel.org/all/20220706150253.2186-1-deller@xxxxxx/ [sudip: adjust context] Signed-off-by: Chen Jun <chenjun102@xxxxxxxxxx> --- drivers/video/console/fbcon.c | 28 ++++++++++++++++++++++++++++ drivers/video/fbdev/core/fbmem.c | 10 +++++++--- include/linux/fbcon.h | 12 ++++++++++++ 3 files changed, 47 insertions(+), 3 deletions(-) create mode 100644 include/linux/fbcon.h diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c index e9eb8aaa2040..2097670b22f7 100644 --- a/drivers/video/console/fbcon.c +++ b/drivers/video/console/fbcon.c @@ -2689,6 +2689,34 @@ static void fbcon_set_all_vcs(struct fb_info *info) 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) { diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 90d918c78f04..b13f6f02633d 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -32,6 +32,7 @@ #include <linux/device.h> #include <linux/efi.h> #include <linux/fb.h> +#include <linux/fbcon.h> #include <linux/overflow.h> #include <asm/fb.h> @@ -1142,9 +1143,12 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, 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))) diff --git a/include/linux/fbcon.h b/include/linux/fbcon.h new file mode 100644 index 000000000000..f3da28242ef4 --- /dev/null +++ b/include/linux/fbcon.h @@ -0,0 +1,12 @@ +#ifndef _LINUX_FBCON_H +#define _LINUX_FBCON_H + +#ifdef CONFIG_FRAMEBUFFER_CONSOLE +int fbcon_modechange_possible(struct fb_info *info, + struct fb_var_screeninfo *var); +#else +static inline int fbcon_modechange_possible(struct fb_info *info, + struct fb_var_screeninfo *var) { return 0; } +#endif + +#endif /* _LINUX_FBCON_H */ -- 2.17.1
