syzbot

random: cc1: uninitialized urandom read (8 bytes read)
audit: type=1400 audit(1537649248.581:9): avc:  denied  { map } for  pid=1826 comm="syz-execprog" path="/root/syzkaller-shm889316429" dev="sda1" ino=16482 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:object_r:file_t:s0 tclass=file permissive=1

======================================================
WARNING: possible circular locking dependency detected
4.14.71+ #8 Not tainted
------------------------------------------------------
syz-executor5/4593 is trying to acquire lock:
 (&sig->cred_guard_mutex){+.+.}, at: [<ffffffff8329e337>] do_io_accounting+0x1d7/0x770 fs/proc/base.c:2717

but task is already holding lock:
 (&p->lock){+.+.}, at: [<ffffffff831d06c4>] seq_read+0xd4/0x11d0 fs/seq_file.c:165

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&p->lock){+.+.}:
       __mutex_lock_common kernel/locking/mutex.c:756 [inline]
       __mutex_lock+0xf5/0x1480 kernel/locking/mutex.c:893
       seq_read+0xd4/0x11d0 fs/seq_file.c:165
       proc_reg_read+0xef/0x170 fs/proc/inode.c:217
       do_loop_readv_writev fs/read_write.c:698 [inline]
       do_iter_read+0x3cc/0x580 fs/read_write.c:922
       vfs_readv+0xe6/0x150 fs/read_write.c:984
       kernel_readv fs/splice.c:361 [inline]
       default_file_splice_read+0x495/0x860 fs/splice.c:416
       do_splice_to+0x102/0x150 fs/splice.c:880
       do_splice fs/splice.c:1173 [inline]
       SYSC_splice fs/splice.c:1402 [inline]
       SyS_splice+0xf4d/0x12a0 fs/splice.c:1382
       do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
       entry_SYSCALL_64_after_hwframe+0x42/0xb7

-> #1 (&pipe->mutex/1){+.+.}:
       __mutex_lock_common kernel/locking/mutex.c:756 [inline]
       __mutex_lock+0xf5/0x1480 kernel/locking/mutex.c:893
       __pipe_lock fs/pipe.c:88 [inline]
       fifo_open+0x156/0x9d0 fs/pipe.c:921
       do_dentry_open+0x426/0xda0 fs/open.c:764
       vfs_open+0x11c/0x210 fs/open.c:878
       do_last fs/namei.c:3408 [inline]
       path_openat+0x4eb/0x23a0 fs/namei.c:3550
       do_filp_open+0x197/0x270 fs/namei.c:3584
       do_open_execat+0x10d/0x5b0 fs/exec.c:849
       do_execveat_common.isra.14+0x6cb/0x1d60 fs/exec.c:1740
       do_execve fs/exec.c:1847 [inline]
       SYSC_execve fs/exec.c:1928 [inline]
       SyS_execve+0x34/0x40 fs/exec.c:1923
       do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
       entry_SYSCALL_64_after_hwframe+0x42/0xb7

-> #0 (&sig->cred_guard_mutex){+.+.}:
       lock_acquire+0x10f/0x380 kernel/locking/lockdep.c:3991
       __mutex_lock_common kernel/locking/mutex.c:756 [inline]
       __mutex_lock+0xf5/0x1480 kernel/locking/mutex.c:893
       do_io_accounting+0x1d7/0x770 fs/proc/base.c:2717
       proc_single_show+0xf1/0x160 fs/proc/base.c:748
       seq_read+0x4e0/0x11d0 fs/seq_file.c:237
       __vfs_read+0xf4/0x5b0 fs/read_write.c:411
       vfs_read+0x11e/0x330 fs/read_write.c:447
       SYSC_pread64 fs/read_write.c:615 [inline]
       SyS_pread64+0x136/0x160 fs/read_write.c:602
       do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
       entry_SYSCALL_64_after_hwframe+0x42/0xb7

other info that might help us debug this:

Chain exists of:
  &sig->cred_guard_mutex --> &pipe->mutex/1 --> &p->lock

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

1 lock held by syz-executor5/4593:
 #0:  (&p->lock){+.+.}, at: [<ffffffff831d06c4>] seq_read+0xd4/0x11d0 fs/seq_file.c:165

stack backtrace:
CPU: 1 PID: 4593 Comm: syz-executor5 Not tainted 4.14.71+ #8
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0xb9/0x11b lib/dump_stack.c:53
 print_circular_bug.isra.18.cold.43+0x2d3/0x40c kernel/locking/lockdep.c:1258
 check_prev_add kernel/locking/lockdep.c:1901 [inline]
 check_prevs_add kernel/locking/lockdep.c:2018 [inline]
 validate_chain kernel/locking/lockdep.c:2460 [inline]
 __lock_acquire+0x2ff9/0x4320 kernel/locking/lockdep.c:3487
 lock_acquire+0x10f/0x380 kernel/locking/lockdep.c:3991
 __mutex_lock_common kernel/locking/mutex.c:756 [inline]
 __mutex_lock+0xf5/0x1480 kernel/locking/mutex.c:893
 do_io_accounting+0x1d7/0x770 fs/proc/base.c:2717
 proc_single_show+0xf1/0x160 fs/proc/base.c:748
 seq_read+0x4e0/0x11d0 fs/seq_file.c:237
 __vfs_read+0xf4/0x5b0 fs/read_write.c:411
 vfs_read+0x11e/0x330 fs/read_write.c:447
 SYSC_pread64 fs/read_write.c:615 [inline]
 SyS_pread64+0x136/0x160 fs/read_write.c:602
 do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x457679
RSP: 002b:00007f3f75f96c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000011
RAX: ffffffffffffffda RBX: 00007f3f75f976d4 RCX: 0000000000457679
RDX: 0000000000000000 RSI: 00000000200012c0 RDI: 0000000000000006
RBP: 000000000072bfa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004d4860 R14: 00000000004c30c2 R15: 0000000000000001