2011-02-06 15:58:15

by Andrea Righi

Subject: [PATCH] fb: fix potential deadlock between lock_fb_info and console_lock

The function 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().

Reported-by: Peter Nordström (Palm GBU) <[email protected]>
Signed-off-by: Andrea Righi <[email protected]>
---
drivers/video/fbmem.c | 24 +++++++++++++++---------
1 files changed, 15 insertions(+), 9 deletions(-)

diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
index e2bf953..def59f0 100644
--- a/drivers/video/fbmem.c
+++ b/drivers/video/fbmem.c
@@ -1034,14 +1034,16 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
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;
@@ -1070,12 +1072,14 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
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;
@@ -1117,14 +1121,16 @@ static long do_fb_ioctl(struct fb_info *info, unsigned int cmd,
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))
--
1.7.1