audit: type=1400 audit(1519637926.711:7): avc:  denied  { map } for  pid=4273 comm="syzkaller092219" path="/root/syzkaller092219473" 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

audit: type=1400 audit(1519637926.711:8): avc:  denied  { map } for  pid=4273 comm="syzkaller092219" path="/dev/ashmem" dev="devtmpfs" ino=1165 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=system_u:object_r:device_t:s0 tclass=chr_file permissive=1
======================================================
WARNING: possible circular locking dependency detected
4.16.0-rc2+ #239 Not tainted
------------------------------------------------------
syzkaller092219/4273 is trying to acquire lock:
 (&mm->mmap_sem){++++}, at: [<00000000bc197c3e>] __might_fault+0xe0/0x1d0 mm/memory.c:4570

but task is already holding lock:
 (ashmem_mutex){+.+.}, at: [<0000000025b2a1db>] ashmem_pin_unpin drivers/staging/android/ashmem.c:705 [inline]
 (ashmem_mutex){+.+.}, at: [<0000000025b2a1db>] ashmem_ioctl+0x3db/0x11b0 drivers/staging/android/ashmem.c:782

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (ashmem_mutex){+.+.}:
       __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
       ashmem_mmap+0x53/0x410 drivers/staging/android/ashmem.c:362
       call_mmap include/linux/fs.h:1786 [inline]
       mmap_region+0xa99/0x15a0 mm/mmap.c:1705
       do_mmap+0x6c0/0xe00 mm/mmap.c:1483
       do_mmap_pgoff include/linux/mm.h:2223 [inline]
       vm_mmap_pgoff+0x1de/0x280 mm/util.c:355
       SYSC_mmap_pgoff mm/mmap.c:1533 [inline]
       SyS_mmap_pgoff+0x462/0x5f0 mm/mmap.c:1491
       do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
       do_fast_syscall_32+0x3ec/0xf9f arch/x86/entry/common.c:392
       entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

-> #0 (&mm->mmap_sem){++++}:
       lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920
       __might_fault+0x13a/0x1d0 mm/memory.c:4571
       _copy_from_user+0x2c/0x110 lib/usercopy.c:10
       copy_from_user include/linux/uaccess.h:147 [inline]
       ashmem_pin_unpin drivers/staging/android/ashmem.c:710 [inline]
       ashmem_ioctl+0x438/0x11b0 drivers/staging/android/ashmem.c:782
       compat_ashmem_ioctl+0x3e/0x50 drivers/staging/android/ashmem.c:813
       C_SYSC_ioctl fs/compat_ioctl.c:1461 [inline]
       compat_SyS_ioctl+0x151/0x2a30 fs/compat_ioctl.c:1407
       do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
       do_fast_syscall_32+0x3ec/0xf9f arch/x86/entry/common.c:392
       entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(ashmem_mutex);
                               lock(&mm->mmap_sem);
                               lock(ashmem_mutex);
  lock(&mm->mmap_sem);

 *** DEADLOCK ***

1 lock held by syzkaller092219/4273:
 #0:  (ashmem_mutex){+.+.}, at: [<0000000025b2a1db>] ashmem_pin_unpin drivers/staging/android/ashmem.c:705 [inline]
 #0:  (ashmem_mutex){+.+.}, at: [<0000000025b2a1db>] ashmem_ioctl+0x3db/0x11b0 drivers/staging/android/ashmem.c:782

stack backtrace:
CPU: 1 PID: 4273 Comm: syzkaller092219 Not tainted 4.16.0-rc2+ #239
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+0x194/0x24d lib/dump_stack.c:53
 print_circular_bug.isra.38+0x2cd/0x2dc kernel/locking/lockdep.c:1223
 check_prev_add kernel/locking/lockdep.c:1863 [inline]
 check_prevs_add kernel/locking/lockdep.c:1976 [inline]
 validate_chain kernel/locking/lockdep.c:2417 [inline]
 __lock_acquire+0x30a8/0x3e00 kernel/locking/lockdep.c:3431
 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3920
 __might_fault+0x13a/0x1d0 mm/memory.c:4571
 _copy_from_user+0x2c/0x110 lib/usercopy.c:10
 copy_from_user include/linux/uaccess.h:147 [inline]
 ashmem_pin_unpin drivers/staging/android/ashmem.c:710 [inline]
 ashmem_ioctl+0x438/0x11b0 drivers/staging/android/ashmem.c:782
 compat_ashmem_ioctl+0x3e/0x50 drivers/staging/android/ashmem.c:813
 C_SYSC_ioctl fs/compat_ioctl.c:1461 [inline]
 compat_SyS_ioctl+0x151/0x2a30 fs/compat_ioctl.c:1407
 do_syscall_32_irqs_on arch/x86/entry/common.c:330 [inline]
 do_fast_syscall_32+0x3ec/0xf9f arch/x86/entry/common.c:392
 entry_SYSENTER_compat+0x70/0x7f arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7efdc99
RSP: 002b:00000000ffb7d5dc EFLAGS: 00000282 ORIG_R