audit: type=1400 audit(1513727379.883:7): avc:  denied  { map } for  pid=3145 comm="syzkaller883040" path="/root/syzkaller883040234" dev="sda1" ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1

======================================================
WARNING: possible circular locking dependency detected
4.15.0-rc4+ #138 Not tainted
------------------------------------------------------
syzkaller883040/3145 is trying to acquire lock:
 (&bdev->bd_mutex){+.+.}, at: [<00000000abac8f72>] blkdev_reread_part+0x1e/0x40 block/ioctl.c:192

but task is already holding lock:
 (&lo->lo_ctl_mutex#2){+.+.}, at: [<00000000253ad9ca>] lo_compat_ioctl+0x109/0x140 drivers/block/loop.c:1538

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&lo->lo_ctl_mutex#2){+.+.}:
       __mutex_lock_common kernel/locking/mutex.c:756 [inline]
       __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893
       mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
       lo_release+0x6b/0x180 drivers/block/loop.c:1592
       __blkdev_put+0x602/0x7c0 fs/block_dev.c:1770
       blkdev_put+0x85/0x4f0 fs/block_dev.c:1835
       blkdev_close+0x8b/0xb0 fs/block_dev.c:1842
       __fput+0x327/0x7e0 fs/file_table.c:210
       ____fput+0x15/0x20 fs/file_table.c:244
       task_work_run+0x199/0x270 kernel/task_work.c:113
       tracehook_notify_resume include/linux/tracehook.h:191 [inline]
       exit_to_usermode_loop+0x296/0x310 arch/x86/entry/common.c:162
       prepare_exit_to_usermode arch/x86/entry/common.c:195 [inline]
       syscall_return_slowpath+0x490/0x550 arch/x86/entry/common.c:264
       entry_SYSCALL_64_fastpath+0x94/0x96

-> #0 (&bdev->bd_mutex){+.+.}:
       lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3914
       __mutex_lock_common kernel/locking/mutex.c:756 [inline]
       __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893
       mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
       blkdev_reread_part+0x1e/0x40 block/ioctl.c:192
       loop_reread_partitions+0x12f/0x1a0 drivers/block/loop.c:619
       loop_set_status+0x9ba/0xf60 drivers/block/loop.c:1161
       loop_set_status_compat+0x92/0xf0 drivers/block/loop.c:1511
       lo_compat_ioctl+0x114/0x140 drivers/block/loop.c:1539
       compat_blkdev_ioctl+0x3ae/0x1840 block/compat_ioctl.c:406
       C_SYSC_ioctl fs/compat_ioctl.c:1473 [inline]
       compat_SyS_ioctl+0x151/0x2a30 fs/compat_ioctl.c:1419
       do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline]
       do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389
       entry_SYSENTER_compat+0x54/0x63 arch/x86/entry/entry_64_compat.S:125

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&lo->lo_ctl_mutex#2);
                               lock(&bdev->bd_mutex);
                               lock(&lo->lo_ctl_mutex#2);
  lock(&bdev->bd_mutex);

 *** DEADLOCK ***

1 lock held by syzkaller883040/3145:
 #0:  (&lo->lo_ctl_mutex#2){+.+.}, at: [<00000000253ad9ca>] lo_compat_ioctl+0x109/0x140 drivers/block/loop.c:1538

stack backtrace:
CPU: 1 PID: 3145 Comm: syzkaller883040 Not tainted 4.15.0-rc4+ #138
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 print_circular_bug.isra.37+0x2cd/0x2dc kernel/locking/lockdep.c:1218
 check_prev_add kernel/locking/lockdep.c:1858 [inline]
 check_prevs_add kernel/locking/lockdep.c:1971 [inline]
 validate_chain kernel/locking/lockdep.c:2412 [inline]
 __lock_acquire+0x30a8/0x3e00 kernel/locking/lockdep.c:3426
 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3914
 __mutex_lock_common kernel/locking/mutex.c:756 [inline]
 __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893
 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
 blkdev_reread_part+0x1e/0x40 block/ioctl.c:192
 loop_reread_partitions+0x12f/0x1a0 drivers/block/loop.c:619
 loop_set_status+0x9ba/0xf60 drivers/block/loop.c:1161
 loop_set_status_compat+0x92/0xf0 drivers/block/loop.c:1511
 lo_compat_ioctl+0x114/0x140 drivers/block/loop.c:1539
 compat_blkdev_ioctl+0x3ae/0x1840 block/compat_ioctl.c:406
 C_SYSC_ioctl fs/compat_ioctl.c:1473 [inline]
 compat_SyS_ioctl+0x151/0x2a30 fs/compat_ioctl.c:1419
 do_syscall_32_irqs_on arch/x86/entry/common.c:327 [inline]
 do_fast_syscall_32+0x3ee/0xf9d arch/x86/entry/common.c:389
 entry_SYSENTER_compat+0x54/0x63 arch/x86/entry/entry_64_compat.S:125
RIP: 0023:0xf7f68c79
RSP: 002b:00000000ffb7ffbc EFLAGS: 00000282 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 0000000000004c02
RDX: 0000000020063f68 RSI: 00000000080ef00c RDI: 000000000000003f
RBP: 0000000000001000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000