From: Andrea Righi <redacted>
Subject: fb: fix potential deadlock between lock_fb_info and console_lock
fb_set_suspend() must be called with the console semaphore held, which
means the code path coming in here will first take the console_lock() and
then call lock_fb_info().
However several framebuffer ioctl commands acquire these locks in reverse
order (lock_fb_info() and then console_lock()). This gives rise to
potential AB-BA deadlock.
Fix this by changing the order of acquisition in the ioctl commands that
make use of console_lock().
Signed-off-by: Andrea Righi <redacted>
Reported-by: Peter Nordström (Palm GBU) <redacted>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <redacted>
---
drivers/video/fbmem.c | 24 +++++++++++++++---------
1 file changed, 15 insertions(+), 9 deletions(-)
diff -puN drivers/video/fbmem.c~fb-fix-potential-deadlock-between-lock_fb_info-and-console_lock drivers/video/fbmem.c
--- a/drivers/video/fbmem.c~fb-fix-potential-deadlock-between-lock_fb_info-and-console_lock
+++ a/drivers/video/fbmem.c
@@ -1076,14 +1076,16 @@ static long do_fb_ioctl(struct fb_info *
case FBIOPUT_VSCREENINFO:
if (copy_from_user(&var, argp, sizeof(var)))
return -EFAULT;
- if (!lock_fb_info(info))
- return -ENODEV;
console_lock();
+ if (!lock_fb_info(info)) {
+ console_unlock();
+ return -ENODEV;
+ }
info->flags |= FBINFO_MISC_USEREVENT;
ret = fb_set_var(info, &var);
info->flags &= ~FBINFO_MISC_USEREVENT;
- console_unlock();
unlock_fb_info(info);
+ console_unlock();
if (!ret && copy_to_user(argp, &var, sizeof(var)))
ret = -EFAULT;
break;@@ -1112,12 +1114,14 @@ static long do_fb_ioctl(struct fb_info *
case FBIOPAN_DISPLAY:
if (copy_from_user(&var, argp, sizeof(var)))
return -EFAULT;
- if (!lock_fb_info(info))
- return -ENODEV;
console_lock();
+ if (!lock_fb_info(info)) {
+ console_unlock();
+ return -ENODEV;
+ }
ret = fb_pan_display(info, &var);
- console_unlock();
unlock_fb_info(info);
+ console_unlock();
if (ret = 0 && copy_to_user(argp, &var, sizeof(var)))
return -EFAULT;
break;@@ -1159,14 +1163,16 @@ static long do_fb_ioctl(struct fb_info *
unlock_fb_info(info);
break;
case FBIOBLANK:
- if (!lock_fb_info(info))
- return -ENODEV;
console_lock();
+ if (!lock_fb_info(info)) {
+ console_unlock();
+ return -ENODEV;
+ }
info->flags |= FBINFO_MISC_USEREVENT;
ret = fb_blank(info, arg);
info->flags &= ~FBINFO_MISC_USEREVENT;
- console_unlock();
unlock_fb_info(info);
+ console_unlock();
break;
default:
if (!lock_fb_info(info))_