======================================================
[ INFO: possible circular locking dependency detected ]
4.4.174+ #4 Not tainted
-------------------------------------------------------
syz-executor.5/31523 is trying to acquire lock:
 (&pipe->mutex/1){+.+.+.}, at: [<ffffffff814b28fd>] __pipe_lock fs/pipe.c:86 [inline]
 (&pipe->mutex/1){+.+.+.}, at: [<ffffffff814b28fd>] fifo_open+0x15d/0xa00 fs/pipe.c:896

but task is already holding lock:
 (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff814acb45>] prepare_bprm_creds+0x55/0x120 fs/exec.c:1225

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

       [<ffffffff81205f6e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff8270e5a2>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff8270e5a2>] mutex_lock_interruptible_nested+0xd2/0xce0 kernel/locking/mutex.c:650
       [<ffffffff815e7f78>] proc_pid_attr_write+0x1a8/0x2a0 fs/proc/base.c:2524
       [<ffffffff81496916>] __vfs_write+0x116/0x3d0 fs/read_write.c:491
       [<ffffffff81496ce2>] __kernel_write+0x112/0x370 fs/read_write.c:513
       [<ffffffff81532e6d>] write_pipe_buf+0x15d/0x1f0 fs/splice.c:1074
       [<ffffffff81533b6e>] splice_from_pipe_feed fs/splice.c:776 [inline]
       [<ffffffff81533b6e>] __splice_from_pipe+0x37e/0x7a0 fs/splice.c:901
       [<ffffffff81536be8>] splice_from_pipe+0x108/0x170 fs/splice.c:936
       [<ffffffff81536cdc>] default_file_splice_write+0x3c/0x80 fs/splice.c:1086
       [<ffffffff81537d31>] do_splice_from fs/splice.c:1128 [inline]
       [<ffffffff81537d31>] do_splice fs/splice.c:1404 [inline]
       [<ffffffff81537d31>] SYSC_splice fs/splice.c:1707 [inline]
       [<ffffffff81537d31>] SyS_splice+0xd71/0x13a0 fs/splice.c:1690
       [<ffffffff82718ba1>] entry_SYSCALL_64_fastpath+0x1e/0x9a

       [<ffffffff81202d86>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
       [<ffffffff81202d86>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
       [<ffffffff81202d86>] validate_chain kernel/locking/lockdep.c:2144 [inline]
       [<ffffffff81202d86>] __lock_acquire+0x37d6/0x4f50 kernel/locking/lockdep.c:3213
       [<ffffffff81205f6e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
       [<ffffffff8270c191>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       [<ffffffff8270c191>] mutex_lock_nested+0xc1/0xb80 kernel/locking/mutex.c:621
       [<ffffffff814b28fd>] __pipe_lock fs/pipe.c:86 [inline]
       [<ffffffff814b28fd>] fifo_open+0x15d/0xa00 fs/pipe.c:896
       [<ffffffff8149154f>] do_dentry_open+0x38f/0xbd0 fs/open.c:749
       [<ffffffff81494d3b>] vfs_open+0x10b/0x210 fs/open.c:862
       [<ffffffff814c5ddf>] do_last fs/namei.c:3269 [inline]
       [<ffffffff814c5ddf>] path_openat+0x136f/0x4470 fs/namei.c:3406
       [<ffffffff814ccab1>] do_filp_open+0x1a1/0x270 fs/namei.c:3440
       [<ffffffff814a7c8c>] do_open_execat+0x10c/0x6e0 fs/exec.c:805
       [<ffffffff814ad306>] do_execveat_common.isra.0+0x6f6/0x1e90 fs/exec.c:1577
       [<ffffffff814af422>] do_execve fs/exec.c:1683 [inline]
       [<ffffffff814af422>] SYSC_execve fs/exec.c:1764 [inline]
       [<ffffffff814af422>] SyS_execve+0x42/0x50 fs/exec.c:1759
       [<ffffffff82718ef5>] return_from_execve+0x0/0x23

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&sig->cred_guard_mutex);
                               lock(&pipe->mutex/1);
                               lock(&sig->cred_guard_mutex);
  lock(&pipe->mutex/1);

 *** DEADLOCK ***

1 lock held by syz-executor.5/31523:
 #0:  (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff814acb45>] prepare_bprm_creds+0x55/0x120 fs/exec.c:1225

stack backtrace:
CPU: 0 PID: 31523 Comm: syz-executor.5 Not tainted 4.4.174+ #4
 0000000000000000 1c0743cbf12b170a ffff8801b77e7530 ffffffff81aad1a1
 ffffffff84057a80 ffff88009d8497c0 ffffffff83abd2b0 ffffffff83ab6860
 ffffffff83abd2b0 ffff8801b77e7580 ffffffff813abcda ffff8801b77e7660
Call Trace:
 [<ffffffff81aad1a1>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81aad1a1>] dump_stack+0xc1/0x120 lib/dump_stack.c:51
 [<ffffffff813abcda>] print_circular_bug.cold+0x2f7/0x44e kernel/locking/lockdep.c:1226
 [<ffffffff81202d86>] check_prev_add kernel/locking/lockdep.c:1853 [inline]
 [<ffffffff81202d86>] check_prevs_add kernel/locking/lockdep.c:1958 [inline]
 [<ffffffff81202d86>] validate_chain kernel/locking/lockdep.c:2144 [inline]
 [<ffffffff81202d86>] __lock_acquire+0x37d6/0x4f50 kernel/locking/lockdep.c:3213
 [<ffffffff81205f6e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
 [<ffffffff8270c191>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<ffffffff8270c191>] mutex_lock_nested+0xc1/0xb80 kernel/locking/mutex.c:621
 [<ffffffff814b28fd>] __pipe_lock fs/pipe.c:86 [inline]
 [<ffffffff814b28fd>] fifo_open+0x15d/0xa00 fs/pipe.c:896
 [<ffffffff8149154f>] do_dentry_open+0x38f/0xbd0 fs/open.c:749
 [<ffffffff81494d3b>] vfs_open+0x10b/0x210 fs/open.c:862
 [<ffffffff814c5ddf>] do_last fs/namei.c:3269 [inline]
 [<ffffffff814c5ddf>] path_openat+0x136f/0x4470 fs/namei.c:3406
 [<ffffffff814ccab1>] do_filp_open+0x1a1/0x270 fs/namei.c:3440
 [<ffffffff814a7c8c>] do_open_execat+0x10c/0x6e0 fs/exec.c:805
 [<ffffffff814ad306>] do_execveat_common.isra.0+0x6f6/0x1e90 fs/exec.c:1577
 [<ffffffff814af422>] do_execve fs/exec.c:1683 [inline]
 [<ffffffff814af422>] SYSC_execve fs/exec.c:1764 [inline]
 [<ffffffff814af422>] SyS_execve+0x42/0x50 fs/exec.c:1759
 [<ffffffff82718ef5>] stub_execve+0x5/0x5 arch/x86/entry/entry_64.S:440
audit: type=1400 audit(1575057667.469:1818): avc:  denied  { create } for  pid=31517 comm="syz-executor.3" 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=0
audit: type=1326 audit(1575057667.609:1819): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 pid=31522 comm="syz-executor.5" exe="/root/syz-executor.5" sig=9 arch=c000003e syscall=228 compat=0 ip=0x45d4ba code=0x0
audit: type=1400 audit(1575057667.739:1820): avc:  denied  { create } for  pid=31550 comm="syz-executor.4" scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_fib_lookup_socket permissive=0
audit: type=1400 audit(1575057667.779:1821): avc:  denied  { create } for  pid=31550 comm="syz-executor.4" scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_fib_lookup_socket permissive=0
audit: type=1400 audit(1575057667.799:1822): avc:  denied  { create } for  pid=31537 comm="syz-executor.3" 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=0
audit: type=1400 audit(1575057667.799:1823): avc:  denied  { create } for  pid=31550 comm="syz-executor.4" scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_fib_lookup_socket permissive=0
audit: type=1400 audit(1575057667.859:1824): avc:  denied  { create } for  pid=31550 comm="syz-executor.4" scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=netlink_fib_lookup_socket permissive=0
audit_printk_skb: 21 callbacks suppressed
audit: type=1400 audit(1575057672.519:1832): avc:  denied  { create } for  pid=31632 comm="syz-executor.2" 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=0
audit: type=1400 audit(1575057672.559:1833): avc:  denied  { create } for  pid=31635 comm="syz-executor.3" 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=0
audit: type=1326 audit(1575057672.569:1834): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 pid=31637 comm="syz-executor.5" exe="/root/syz-executor.5" sig=9 arch=c000003e syscall=228 compat=0 ip=0x45d4ba code=0x0
audit: type=1400 audit(1575057673.819:1835): avc:  denied  { create } for  pid=31675 comm="syz-executor.2" 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=0
audit: type=1400 audit(1575057673.819:1836): avc:  denied  { create } for  pid=31676 comm="syz-executor.3" 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=0
audit: type=1326 audit(1575057673.879:1837): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 pid=31677 comm="syz-executor.5" exe="/root/syz-executor.5" sig=9 arch=c000003e syscall=228 compat=0 ip=0x45d4ba code=0x0
audit: type=1326 audit(1575057674.629:1838): auid=4294967295 uid=0 gid=0 ses=4294967295 subj=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 pid=31744 comm="syz-executor.5" exe="/root/syz-executor.5" sig=9 arch=c000003e syscall=228 compat=0 ip=0x45d4ba code=0x0
audit: type=1400 audit(1575057674.659:1839): avc:  denied  { create } for  pid=31734 comm="syz-executor.3" 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=0
audit: type=1400 audit(1575057674.689:1840): avc:  denied  { create } for  pid=31739 comm="syz-executor.2" 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=0