On 12/30/22 07:35, Hang Zhang wrote:
In do_fb_ioctl(), user specified "fb_info" can be freed in the callee fbcon_get_con2fb_map_ioctl() -> set_con2fb_map() -> con2fb_release_oldinfo(), this free operation is protected by console_lock() in fbcon_set_con2fb_map_ioctl(), it also results in the change of certain states such as "minfo->dead" in matroxfb_remove(), so that it can be checked to avoid use-after-free before the use sites (e.g., the check at the beginning of matroxfb_ioctl()). However, the problem is that the use site is not protected by the same locks as for the free operation, e.g., "default" case in do_fb_ioctl() can lead to "matroxfb_ioctl()" but it's not protected by console_lock(), which can invalidate the aforementioned state set and check in a concurrent setting. Prevent the potential use-after-free issues by protecting the "default" case in do_fb_ioctl() with console_lock(), similarly as for many other cases like "case FBIOBLANK" and "case FBIOPAN_DISPLAY". Signed-off-by: Hang Zhang <zh.nvgt@xxxxxxxxx>
applied to fbdev git tree. Thanks, Helge
--- drivers/video/fbdev/core/fbmem.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 1e70d8c67653..8b1a1527d18a 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1182,6 +1182,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, console_unlock(); break; default: + console_lock(); lock_fb_info(info); fb = info->fbops; if (fb->fb_ioctl) @@ -1189,6 +1190,7 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd, else ret = -ENOTTY; unlock_fb_info(info); + console_unlock(); } return ret; }
