======================================================
[ INFO: possible circular locking dependency detected ]
4.4.118-g5f7f76a #24 Not tainted
-------------------------------------------------------
syz-executor7/15285 is trying to acquire lock:
 (&mm->mmap_sem){++++++}, at: [<ffffffff81495644>] __might_fault+0xe4/0x1d0 mm/memory.c:3809

but task is already holding lock:
 (ashmem_mutex){+.+.+.}, at: [<ffffffff82c627f7>] ashmem_pin_unpin drivers/staging/android/ashmem.c:701 [inline]
 (ashmem_mutex){+.+.+.}, at: [<ffffffff82c627f7>] ashmem_ioctl+0x367/0xfa0 drivers/staging/android/ashmem.c:778
audit: type=1400 audit(1519668642.647:115): avc:  denied  { create } for  pid=15295 comm="syz-executor6" scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_generic_socket permissive=1
audit: type=1400 audit(1519668642.667:116): avc:  denied  { create } for  pid=15295 comm="syz-executor6" scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_generic_socket permissive=1

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

       [<ffffffff8123d7ce>] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592
       [<ffffffff8376948b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff8376948b>] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621
       [<ffffffff82c613b3>] ashmem_mmap+0x53/0x400 drivers/staging/android/ashmem.c:366
       [<ffffffff814b0e0f>] mmap_region+0x94f/0x1250 mm/mmap.c:1664
       [<ffffffff814b1c0d>] do_mmap+0x4fd/0x9d0 mm/mmap.c:1441
       [<ffffffff8147008e>] do_mmap_pgoff include/linux/mm.h:1915 [inline]
       [<ffffffff8147008e>] vm_mmap_pgoff+0x16e/0x1c0 mm/util.c:296
       [<ffffffff814afddf>] SYSC_mmap_pgoff mm/mmap.c:1491 [inline]
       [<ffffffff814afddf>] SyS_mmap_pgoff+0x33f/0x560 mm/mmap.c:1449
       [<ffffffff8101beb6>] SYSC_mmap arch/x86/kernel/sys_x86_64.c:95 [inline]
       [<ffffffff8101beb6>] SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:86
       [<ffffffff83772a5f>] entry_SYSCALL_64_fastpath+0x1c/0x98

       [<ffffffff8123ab2f>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
       [<ffffffff8123ab2f>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
       [<ffffffff8123ab2f>] validate_chain kernel/locking/lockdep.c:2144 [inline]
       [<ffffffff8123ab2f>] __lock_acquire+0x371f/0x4b50 kernel/locking/lockdep.c:3213
       [<ffffffff8123d7ce>] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592
       [<ffffffff814956aa>] __might_fault+0x14a/0x1d0 mm/memory.c:3810
       [<ffffffff82c62844>] copy_from_user arch/x86/include/asm/uaccess.h:724 [inline]
       [<ffffffff82c62844>] ashmem_pin_unpin drivers/staging/android/ashmem.c:706 [inline]
       [<ffffffff82c62844>] ashmem_ioctl+0x3b4/0xfa0 drivers/staging/android/ashmem.c:778
       [<ffffffff81559d4a>] vfs_ioctl fs/ioctl.c:43 [inline]
       [<ffffffff81559d4a>] do_vfs_ioctl+0x7aa/0xee0 fs/ioctl.c:607
       [<ffffffff8155a50f>] SYSC_ioctl fs/ioctl.c:622 [inline]
       [<ffffffff8155a50f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:613
       [<ffffffff83772a5f>] entry_SYSCALL_64_fastpath+0x1c/0x98

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 syz-executor7/15285:
 #0:  (ashmem_mutex){+.+.+.}, at: [<ffffffff82c627f7>] ashmem_pin_unpin drivers/staging/android/ashmem.c:701 [inline]
 #0:  (ashmem_mutex){+.+.+.}, at: [<ffffffff82c627f7>] ashmem_ioctl+0x367/0xfa0 drivers/staging/android/ashmem.c:778

stack backtrace:
CPU: 0 PID: 15285 Comm: syz-executor7 Not tainted 4.4.118-g5f7f76a #24
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 4080d0340ae8c213 ffff8800b9f7f9b8 ffffffff81d0402d
 ffffffff851a0010 ffffffff851a0010 ffffffff851bee80 ffff8800b30150f8
 ffff8800b3014800 ffff8800b9f7fa00 ffffffff81233ba1 ffff8800b30150f8
Call Trace:
 [<ffffffff81d0402d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d0402d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff81233ba1>] print_circular_bug+0x271/0x310 kernel/locking/lockdep.c:1226
 [<ffffffff8123ab2f>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
 [<ffffffff8123ab2f>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
 [<ffffffff8123ab2f>] validate_chain kernel/locking/lockdep.c:2144 [inline]
 [<ffffffff8123ab2f>] __lock_acquire+0x371f/0x4b50 kernel/locking/lockdep.c:3213
 [<ffffffff8123d7ce>] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592
 [<ffffffff814956aa>] __might_fault+0x14a/0x1d0 mm/memory.c:3810
 [<ffffffff82c62844>] copy_from_user arch/x86/include/asm/uaccess.h:724 [inline]
 [<ffffffff82c62844>] ashmem_pin_unpin drivers/staging/android/ashmem.c:706 [inline]
 [<ffffffff82c62844>] ashmem_ioctl+0x3b4/0xfa0 drivers/staging/android/ashmem.c:778
 [<ffffffff81559d4a>] vfs_ioctl fs/ioctl.c:43 [inline]
 [<ffffffff81559d4a>] do_vfs_ioctl+0x7aa/0xee0 fs/ioctl.c:607
 [<ffffffff8155a50f>] SYSC_ioctl fs/ioctl.c:622 [inline]
 [<ffffffff8155a50f>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:613
 [<ffffffff83772a5f>] entry_SYSCALL_64_fastpath+0x1c/0x98