Subject: WARNING in _copy_to_user

From: syzbot <[email-masked]>
Date: Fri, 01 Dec 2017 03:30:01 -0800

Hello,

syzkaller hit the following crash on  
df8ba95c572a187ed2aa7403e97a7a7f58c01f00
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.

Unfortunately, I don't have any reproducer for this bug yet.

=====================================
WARNING: bad unlock balance detected!
4.15.0-rc1+ #202 Not tainted
-------------------------------------
syz-executor4/28722 is trying to release lock (mrt_lock) at:
[<00000000c358606b>] ipmr_mfc_seq_stop+0xe1/0x130 net/ipv6/ip6mr.c:553
but there are no more locks to release!

other info that might help us debug this:
2 locks held by syz-executor4/28722:
  #0:  (sb_writers#6){.+.+}, at: [<000000003332d098>] file_start_write  
include/linux/fs.h:2715 [inline]
  #0:  (sb_writers#6){.+.+}, at: [<000000003332d098>]  
do_sendfile+0xaec/0xe90 fs/read_write.c:1412
  #1:  (&p->lock){+.+.}, at: [<000000001572c807>] seq_read+0xd5/0x13d0  
fs/seq_file.c:165

stack backtrace:
CPU: 0 PID: 28722 Comm: syz-executor4 Not tainted 4.15.0-rc1+ #202
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
Call Trace:
  __dump_stack lib/dump_stack.c:17 [inline]
  dump_stack+0x194/0x257 lib/dump_stack.c:53
  print_unlock_imbalance_bug+0x12f/0x140 kernel/locking/lockdep.c:3561
  __lock_release kernel/locking/lockdep.c:3775 [inline]
  lock_release+0x5f9/0xda0 kernel/locking/lockdep.c:4023
  __raw_read_unlock include/linux/rwlock_api_smp.h:225 [inline]
  _raw_read_unlock+0x1a/0x30 kernel/locking/spinlock.c:255
  ipmr_mfc_seq_stop+0xe1/0x130 net/ipv6/ip6mr.c:553
  seq_read+0xc42/0x13d0 fs/seq_file.c:277
  proc_reg_read+0xef/0x170 fs/proc/inode.c:217
  do_loop_readv_writev fs/read_write.c:673 [inline]
  do_iter_read+0x3db/0x5b0 fs/read_write.c:897
  vfs_readv+0x121/0x1c0 fs/read_write.c:959
  kernel_readv fs/splice.c:361 [inline]
  default_file_splice_read+0x508/0xae0 fs/splice.c:416
  do_splice_to+0x110/0x170 fs/splice.c:880
  splice_direct_to_actor+0x242/0x820 fs/splice.c:952
  do_splice_direct+0x2a7/0x3d0 fs/splice.c:1061
  do_sendfile+0x5d5/0xe90 fs/read_write.c:1413
  SYSC_sendfile64 fs/read_write.c:1468 [inline]
  SyS_sendfile64+0xbd/0x160 fs/read_write.c:1460
  entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x4529d9
RSP: 002b:00007f225b206c58 EFLAGS: 00000212 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 0000000000758020 RCX: 00000000004529d9
RDX: 0000000020360ff8 RSI: 0000000000000014 RDI: 0000000000000014
RBP: 0000000000000561 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000008 R11: 0000000000000212 R12: 00000000006f51b8
R13: 00000000ffffffff R14: 00007f225b2076d4 R15: 0000000000000000
WARNING: CPU: 0 PID: 28722 at lib/usercopy.c:26 _copy_to_user+0xb5/0xc0  
lib/usercopy.c:26

---
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