在 2022/8/5 14:09, Cengiz Can 写道:
On Thu, 2022-08-04 at 12:27 +0000, Chen Jun wrote:
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 [Chen Jun: adjust context] Signed-off-by: Chen Jun chenjun102@huawei.com
drivers/video/fbdev/core/fbcon.c | 28 ++++++++++++++++++++++++++++ drivers/video/fbdev/core/fbmem.c | 10 +++++++--- include/linux/fbcon.h | 4 ++++ 3 files changed, 39 insertions(+), 3 deletions(-)
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c index a97e94b1c84f..b84264e98929 100644 --- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c @@ -2706,6 +2706,34 @@ 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 9087d467cc46..264e8ca5efa7 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1134,9 +1134,13 @@ 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;}lock_fb_info(info);Why do we lock and unlock here consecutively?
Can it be a leftover?
Because in upstream commit, lock encapsulates `fb_set_var`, `fbcon_modechange_possible` and `fbcon_update_vcs` calls, which makes sense.
Here, it doesn't.
Thanks, lock_fb_info(info) is wrong here.
console_unlock(); if (!ret && copy_to_user(argp, &var, sizeof(var)))diff --git a/include/linux/fbcon.h b/include/linux/fbcon.h index f68a7db14165..39939d55c834 100644 --- 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);+static inline int fbcon_modechange_possible(struct fb_info *info,
struct fb_var_screeninfo *var) { return 0; }#endif /* _LINUX_FBCON_H */