From b3f3107fbd928fed6e4fecbe3da2ed5f43216439 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa Date: Thu, 8 Nov 2018 14:01:02 +0100 Subject: block/loop: Use global lock for ioctl() operation. commit 310ca162d779efee8a2dc3731439680f3e9c1e86 upstream. syzbot is reporting NULL pointer dereference [1] which is caused by race condition between ioctl(loop_fd, LOOP_CLR_FD, 0) versus ioctl(other_loop_fd, LOOP_SET_FD, loop_fd) due to traversing other loop devices at loop_validate_file() without holding corresponding lo->lo_ctl_mutex locks. Since ioctl() request on loop devices is not frequent operation, we don't need fine grained locking. Let's use global lock in order to allow safe traversal at loop_validate_file(). Note that syzbot is also reporting circular locking dependency between bdev->bd_mutex and lo->lo_ctl_mutex [2] which is caused by calling blkdev_reread_part() with lock held. This patch does not address it. [1] https://syzkaller.appspot.com/bug?id=f3cfe26e785d85f9ee259f385515291d21bd80a3 [2] https://syzkaller.appspot.com/bug?id=bf154052f0eea4bc7712499e4569505907d15889 Signed-off-by: Tetsuo Handa Reported-by: syzbot Reviewed-by: Jan Kara Signed-off-by: Jan Kara Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- drivers/block/loop.h | 1 - 1 file changed, 1 deletion(-) (limited to 'drivers/block/loop.h') diff --git a/drivers/block/loop.h b/drivers/block/loop.h index 60f0fd2c0c65..a923e74495ce 100644 --- a/drivers/block/loop.h +++ b/drivers/block/loop.h @@ -55,7 +55,6 @@ struct loop_device { spinlock_t lo_lock; int lo_state; - struct mutex lo_ctl_mutex; struct kthread_worker worker; struct task_struct *worker_task; bool use_dio; -- cgit v1.2.3