syzbot

random: cc1: uninitialized urandom read (8 bytes read)
audit: type=1400 audit(1539634773.910:9): avc:  denied  { map } for  pid=1787 comm="syz-execprog" path="/root/syzkaller-shm608069533" 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
4.14.76+ #19 Not tainted
------------------------------------------------------
syz-executor5/4863 is trying to acquire lock:
 (&sig->cred_guard_mutex){+.+.}, at: [<ffffffff8a6a320f>] lock_trace+0x3f/0xc0 fs/proc/base.c:408

but task is already holding lock:
 (&p->lock){+.+.}, at: [<ffffffff8a5d0bb4>] 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
       lock_trace+0x3f/0xc0 fs/proc/base.c:408
       proc_pid_syscall+0xa2/0x240 fs/proc/base.c:640
       proc_single_show+0xf1/0x160 fs/proc/base.c:762
       seq_read+0x4e0/0x11d0 fs/seq_file.c:237
       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
       splice_direct_to_actor+0x21d/0x750 fs/splice.c:952
       do_splice_direct+0x17b/0x220 fs/splice.c:1061
       do_sendfile+0x4a1/0xb50 fs/read_write.c:1438
       SYSC_sendfile64 fs/read_write.c:1493 [inline]
       SyS_sendfile64+0xab/0x140 fs/read_write.c:1485
       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 ***

2 locks held by syz-executor5/4863:
 #0:  (sb_writers#7){.+.+}, at: [<ffffffff8a559d55>] file_start_write include/linux/fs.h:2722 [inline]
 #0:  (sb_writers#7){.+.+}, at: [<ffffffff8a559d55>] do_sendfile+0x9b5/0xb50 fs/read_write.c:1437
 #1:  (&p->lock){+.+.}, at: [<ffffffff8a5d0bb4>] seq_read+0xd4/0x11d0 fs/seq_file.c:165

stack backtrace:
CPU: 1 PID: 4863 Comm: syz-executor5 Not tainted 4.14.76+ #19
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
 lock_trace+0x3f/0xc0 fs/proc/base.c:408
 proc_pid_syscall+0xa2/0x240 fs/proc/base.c:640
 proc_single_show+0xf1/0x160 fs/proc/base.c:762
 seq_read+0x4e0/0x11d0 fs/seq_file.c:237
 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
 splice_direct_to_actor+0x21d/0x750 fs/splice.c:952
 do_splice_direct+0x17b/0x220 fs/splice.c:1061
 do_sendfile+0x4a1/0xb50 fs/read_write.c:1438
 SYSC_sendfile64 fs/read_write.c:1493 [inline]
 SyS_sendfile64+0xab/0x140 fs/read_write.c:1485
 do_syscall_64+0x19b/0x4b0 arch/x86/entry/common.c:289
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x457569
RSP: 002b:00007f78a3449c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 0000000000000004 RCX: 0000000000457569
RDX: 0000000020000240 RSI: 0000000000000007 RDI: 0000000000000006
RBP: 000000000072bfa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 00007f78a344a6d4
R13: 00000000004c34d0 R14: 00000000004d5298 R15: 00000000ffffffff