======================================================
[ INFO: possible circular locking dependency detected ]
4.9.186+ #14 Not tainted
-------------------------------------------------------
syz-executor.4/32153 is trying to acquire lock:
 (&p->lock){+.+.+.}, at: [<00000000234ece4d>] seq_read+0xd6/0x1250 fs/seq_file.c:178
but task is already holding lock:
 (&sig->cred_guard_mutex){+.+.+.}, at: [<0000000071573381>] prepare_bprm_creds+0x55/0x120 fs/exec.c:1369
which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

       lock_acquire+0x133/0x3d0 kernel/locking/lockdep.c:3756
       __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       mutex_lock_killable_nested+0xcd/0xa10 kernel/locking/mutex.c:641
       lock_trace+0x44/0xc0 fs/proc/base.c:431
       proc_pid_syscall+0x9b/0x250 fs/proc/base.c:663
       proc_single_show+0xf6/0x160 fs/proc/base.c:785
       seq_read+0x4cd/0x1250 fs/seq_file.c:240
       do_loop_readv_writev.part.0+0xcc/0x2c0 fs/read_write.c:721
       do_loop_readv_writev fs/read_write.c:710 [inline]
       do_readv_writev+0x556/0x7a0 fs/read_write.c:876
       vfs_readv+0x86/0xc0 fs/read_write.c:900
       kernel_readv fs/splice.c:363 [inline]
       default_file_splice_read+0x44b/0x7e0 fs/splice.c:435
       do_splice_to+0x108/0x170 fs/splice.c:899
       splice_direct_to_actor+0x246/0x820 fs/splice.c:971
       do_splice_direct+0x1a5/0x260 fs/splice.c:1080
       do_sendfile+0x503/0xc00 fs/read_write.c:1402
       SYSC_sendfile64 fs/read_write.c:1463 [inline]
       SyS_sendfile64+0x145/0x160 fs/read_write.c:1449
       do_syscall_64+0x1ad/0x5c0 arch/x86/entry/common.c:288
       entry_SYSCALL_64_after_swapgs+0x5d/0xdb

       check_prev_add kernel/locking/lockdep.c:1828 [inline]
       check_prevs_add kernel/locking/lockdep.c:1938 [inline]
       validate_chain kernel/locking/lockdep.c:2265 [inline]
       __lock_acquire+0x2d10/0x4350 kernel/locking/lockdep.c:3345
       lock_acquire+0x133/0x3d0 kernel/locking/lockdep.c:3756
       __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       mutex_lock_nested+0xc7/0x920 kernel/locking/mutex.c:621
       seq_read+0xd6/0x1250 fs/seq_file.c:178
       __vfs_read+0x116/0x550 fs/read_write.c:451
       vfs_read+0x137/0x380 fs/read_write.c:474
       kernel_read+0x103/0x1b0 fs/exec.c:893
       prepare_binprm fs/exec.c:1549 [inline]
       prepare_binprm+0x575/0x770 fs/exec.c:1536
       do_execveat_common.isra.0+0xd09/0x1db0 fs/exec.c:1766
       do_execveat fs/exec.c:1840 [inline]
       SYSC_execveat fs/exec.c:1921 [inline]
       SyS_execveat+0x55/0x70 fs/exec.c:1913
       do_syscall_64+0x1ad/0x5c0 arch/x86/entry/common.c:288
       entry_SYSCALL_64_after_swapgs+0x5d/0xdb

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-executor.4/32153:
 #0:  (&sig->cred_guard_mutex){+.+.+.}, at: [<0000000071573381>] prepare_bprm_creds+0x55/0x120 fs/exec.c:1369

stack backtrace:
CPU: 1 PID: 32153 Comm: syz-executor.4 Not tainted 4.9.186+ #14
 ffff8801c5a57668 ffffffff81b660c1 ffffffff83cb0f00 ffffffff83caf5b0
 ffffffff83cb0f00 ffffffff84250f80 ffff8801a7008000 ffff8801c5a576c0
 ffffffff814053dc ffff8801a7008000 ffff8801c5a577b0 ffff8801a70088d8
Call Trace:
 [<0000000085f75f42>] __dump_stack lib/dump_stack.c:15 [inline]
 [<0000000085f75f42>] dump_stack+0xc1/0x120 lib/dump_stack.c:51
 [<000000002eef8033>] print_circular_bug.cold+0x2f6/0x454 kernel/locking/lockdep.c:1202
 [<000000004ecb5502>] check_prev_add kernel/locking/lockdep.c:1828 [inline]
 [<000000004ecb5502>] check_prevs_add kernel/locking/lockdep.c:1938 [inline]
 [<000000004ecb5502>] validate_chain kernel/locking/lockdep.c:2265 [inline]
 [<000000004ecb5502>] __lock_acquire+0x2d10/0x4350 kernel/locking/lockdep.c:3345
 [<00000000999278e7>] lock_acquire+0x133/0x3d0 kernel/locking/lockdep.c:3756
 [<00000000676911f8>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<00000000676911f8>] mutex_lock_nested+0xc7/0x920 kernel/locking/mutex.c:621
 [<00000000234ece4d>] seq_read+0xd6/0x1250 fs/seq_file.c:178
 [<0000000049cbc757>] __vfs_read+0x116/0x550 fs/read_write.c:451
 [<000000002384ec41>] vfs_read+0x137/0x380 fs/read_write.c:474
 [<0000000041c5cd35>] kernel_read+0x103/0x1b0 fs/exec.c:893
 [<000000004ac9d4d9>] prepare_binprm fs/exec.c:1549 [inline]
 [<000000004ac9d4d9>] prepare_binprm+0x575/0x770 fs/exec.c:1536
 [<00000000290875a7>] do_execveat_common.isra.0+0xd09/0x1db0 fs/exec.c:1766
 [<00000000ef6c145a>] do_execveat fs/exec.c:1840 [inline]
 [<00000000ef6c145a>] SYSC_execveat fs/exec.c:1921 [inline]
 [<00000000ef6c145a>] SyS_execveat+0x55/0x70 fs/exec.c:1913
 [<00000000ad08d513>] do_syscall_64+0x1ad/0x5c0 arch/x86/entry/common.c:288
 [<00000000ad1207a7>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb