======================================================
[ INFO: possible circular locking dependency detected ]
4.4.132-g4f75c34 #42 Not tainted
-------------------------------------------------------
syz-executor5/8009 is trying to acquire lock:
 (&p->lock){+.+.+.}, at: [<ffffffff8158d0bd>] seq_read+0xdd/0x12d0 fs/seq_file.c:178

but task is already holding lock:
 (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff81532443>] prepare_bprm_creds+0x53/0x110 fs/exec.c:1221

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

       [<ffffffff8123585e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff838b7f2c>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff838b7f2c>] mutex_lock_killable_nested+0xcc/0x980 kernel/locking/mutex.c:641
       [<ffffffff81673394>] lock_trace+0x44/0xc0 fs/proc/base.c:446
       [<ffffffff81673b79>] proc_pid_syscall+0xa9/0x260 fs/proc/base.c:667
       [<ffffffff8167495d>] proc_single_show+0xfd/0x170 fs/proc/base.c:789
       [<ffffffff8158d496>] seq_read+0x4b6/0x12d0 fs/seq_file.c:240
       [<ffffffff8151c08c>] __vfs_read+0x11c/0x3e0 fs/read_write.c:432
       [<ffffffff8151de80>] vfs_read+0x130/0x360 fs/read_write.c:454
       [<ffffffff81520a75>] SYSC_pread64 fs/read_write.c:607 [inline]
       [<ffffffff81520a75>] SyS_pread64+0x145/0x170 fs/read_write.c:594
       [<ffffffff81115359>] sys32_pread+0x39/0x50 arch/x86/ia32/sys_ia32.c:179
       [<ffffffff81006d96>] do_syscall_32_irqs_on arch/x86/entry/common.c:392 [inline]
       [<ffffffff81006d96>] do_fast_syscall_32+0x326/0x8b0 arch/x86/entry/common.c:459
       [<ffffffff838c1b6a>] sysenter_flags_fixed+0xd/0x17

       [<ffffffff81232712>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
       [<ffffffff81232712>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
       [<ffffffff81232712>] validate_chain kernel/locking/lockdep.c:2144 [inline]
       [<ffffffff81232712>] __lock_acquire+0x3902/0x5270 kernel/locking/lockdep.c:3213
       [<ffffffff8123585e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff838b889b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff838b889b>] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621
       [<ffffffff8158d0bd>] seq_read+0xdd/0x12d0 fs/seq_file.c:178
       [<ffffffff8151c08c>] __vfs_read+0x11c/0x3e0 fs/read_write.c:432
       [<ffffffff8151de80>] vfs_read+0x130/0x360 fs/read_write.c:454
       [<ffffffff8152dc13>] kernel_read+0xf3/0x1a0 fs/exec.c:849
       [<ffffffff8152f4e7>] prepare_binprm+0x577/0x750 fs/exec.c:1396
       [<ffffffff815333d3>] do_execveat_common.isra.36+0xed3/0x1f10 fs/exec.c:1616
       [<ffffffff81534ebb>] compat_do_execveat fs/exec.c:1722 [inline]
       [<ffffffff81534ebb>] C_SYSC_execveat fs/exec.c:1792 [inline]
       [<ffffffff81534ebb>] compat_SyS_execveat+0x5b/0x70 fs/exec.c:1784
       [<ffffffff81006d96>] do_syscall_32_irqs_on arch/x86/entry/common.c:392 [inline]
       [<ffffffff81006d96>] do_fast_syscall_32+0x326/0x8b0 arch/x86/entry/common.c:459
       [<ffffffff838c1b6a>] sysenter_flags_fixed+0xd/0x17

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&sig->cred_guard_mutex);
                               lock(&p->lock);
                               lock(&sig->cred_guard_mutex);
  lock(&p->lock);

 *** DEADLOCK ***

1 lock held by syz-executor5/8009:
 #0:  (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff81532443>] prepare_bprm_creds+0x53/0x110 fs/exec.c:1221

stack backtrace:
CPU: 0 PID: 8009 Comm: syz-executor5 Not tainted 4.4.132-g4f75c34 #42
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 9c1f8eb17c9e2989 ffff8801bac9f608 ffffffff81e0df8d
 ffffffff853d0060 ffffffff8539e3e0 ffffffff853d0060 ffff8801d60de900
 ffff8801d60de000 ffff8801bac9f650 ffffffff8140e30b 0000000000000001
Call Trace:
 [<ffffffff81e0df8d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81e0df8d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff8140e30b>] print_circular_bug.cold.50+0x1bd/0x27d kernel/locking/lockdep.c:1226
 [<ffffffff81232712>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
 [<ffffffff81232712>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
 [<ffffffff81232712>] validate_chain kernel/locking/lockdep.c:2144 [inline]
 [<ffffffff81232712>] __lock_acquire+0x3902/0x5270 kernel/locking/lockdep.c:3213
 [<ffffffff8123585e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
 [<ffffffff838b889b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<ffffffff838b889b>] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621
 [<ffffffff8158d0bd>] seq_read+0xdd/0x12d0 fs/seq_file.c:178
 [<ffffffff8151c08c>] __vfs_read+0x11c/0x3e0 fs/read_write.c:432
 [<ffffffff8151de80>] vfs_read+0x130/0x360 fs/read_write.c:454
 [<ffffffff8152dc13>] kernel_read+0xf3/0x1a0 fs/exec.c:849
 [<ffffffff8152f4e7>] prepare_binprm+0x577/0x750 fs/exec.c:1396
 [<ffffffff815333d3>] do_execveat_common.isra.36+0xed3/0x1f10 fs/exec.c:1616
 [<ffffffff81534ebb>] compat_do_execveat fs/exec.c:1722 [inline]
 [<ffffffff81534ebb>] C_SYSC_execveat fs/exec.c:1792 [inline]
 [<ffffffff81534ebb>] compat_SyS_execveat+0x5b/0x70 fs/exec.c:1784
 [<ffffffff81006d96>] do_syscall_32_irqs_on arch/x86/entry/common.c:392 [inline]
 [<ffffffff81006d96>] do_fast_syscall_32+0x326/0x8b0 arch/x86/entry/common.c:459
 [<ffffffff838c1b6a>] sysenter_flags_fixed+0xd/0x17