Subject: Re: WARNING: ODEBUG bug in do_ipt_get_ctl

From: Eric Biggers <[email-masked]>
Date: Wed, 4 Jul 2018 14:19:40 -0700

On Sun, Feb 25, 2018 at 08:22:01AM -0800, syzbot wrote:
> syzbot has found reproducer for the following crash on net-next commit
> f74290fdb363665538743d14c4f00aeacdb68d87 (Sat Feb 24 05:04:20 2018 +0000)
> Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
> 
> So far this crash happened 3 times on net-next, upstream.
> C reproducer is attached.
> syzkaller reproducer is attached.
> Raw console output is attached.
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached.
> 
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: [email-masked]
> It will help syzbot understand when the bug is fixed.
> 
> ------------[ cut here ]------------
> ODEBUG: free active (active state 0) object type: timer_list hint:
> delayed_work_timer_fn+0x0/0x90 kernel/workqueue.c:1355
> WARNING: CPU: 1 PID: 4244 at lib/debugobjects.c:291
> debug_print_object+0x166/0x220 lib/debugobjects.c:288
> Kernel panic - not syncing: panic_on_warn set ...
> 
> CPU: 1 PID: 4244 Comm: syzkaller150583 Not tainted 4.16.0-rc2+ #241
> 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+0x194/0x24d lib/dump_stack.c:53
>  panic+0x1e4/0x41c kernel/panic.c:183
>  __warn+0x1dc/0x200 kernel/panic.c:547
>  report_bug+0x211/0x2d0 lib/bug.c:184
>  fixup_bug.part.11+0x37/0x80 arch/x86/kernel/traps.c:178
>  fixup_bug arch/x86/kernel/traps.c:247 [inline]
>  do_error_trap+0x2d7/0x3e0 arch/x86/kernel/traps.c:296
>  do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:315
>  invalid_op+0x58/0x80 arch/x86/entry/entry_64.S:957
> RIP: 0010:debug_print_object+0x166/0x220 lib/debugobjects.c:288
> RSP: 0018:ffff8801cc2c7778 EFLAGS: 00010082
> RAX: dffffc0000000008 RBX: 0000000000000003 RCX: ffffffff815abe7e
> RDX: 0000000000000000 RSI: 1ffff10039858e9f RDI: 1ffff10039858e74
> RBP: ffff8801cc2c77b8 R08: 0000000000000000 R09: 1ffff10039858e46
> R10: ffffed0039858f1e R11: ffffffff86f395b8 R12: 0000000000000001
> R13: ffffffff86f4ae20 R14: ffffffff86407fa0 R15: ffffffff815fe8e0
>  __debug_check_no_obj_freed lib/debugobjects.c:745 [inline]
>  debug_check_no_obj_freed+0x662/0xf1f lib/debugobjects.c:774
>  __vunmap+0x112/0x380 mm/vmalloc.c:1530
>  vfree+0x50/0xe0 mm/vmalloc.c:1606
>  copy_entries_to_user net/ipv4/netfilter/ip_tables.c:880 [inline]
>  get_entries net/ipv4/netfilter/ip_tables.c:1035 [inline]
>  do_ipt_get_ctl+0x7f5/0xac0 net/ipv4/netfilter/ip_tables.c:1708
>  nf_sockopt net/netfilter/nf_sockopt.c:104 [inline]
>  nf_getsockopt+0x6a/0xc0 net/netfilter/nf_sockopt.c:122
>  ip_getsockopt+0x152/0x200 net/ipv4/ip_sockglue.c:1572
>  tcp_getsockopt+0x82/0xd0 net/ipv4/tcp.c:3332
>  sock_common_getsockopt+0x95/0xd0 net/core/sock.c:2938
>  SYSC_getsockopt net/socket.c:1881 [inline]
>  SyS_getsockopt+0x178/0x340 net/socket.c:1863
>  do_syscall_64+0x280/0x940 arch/x86/entry/common.c:287
>  entry_SYSCALL_64_after_hwframe+0x42/0xb7
> RIP: 0033:0x455faa
> RSP: 002b:000000000080e8c8 EFLAGS: 00000216 ORIG_RAX: 0000000000000037
> RAX: ffffffffffffffda RBX: 00000000006ea840 RCX: 0000000000455faa
> RDX: 0000000000000041 RSI: 0000000000000000 RDI: 0000000000000004
> RBP: 00000000006ea840 R08: 000000000080e8ec R09: 0000000000004000
> R10: 000000000080e9f0 R11: 0000000000000216 R12: 0000000000000004
> R13: 000000000080e9f0 R14: 000000000080e8f0 R15: 0000000000000000

This last occurred 4 months ago, the report doesn't make sense, and I can't
reproduce it even with the same kernel commit, kernel config, and C repro syzbot
gave.  The "debug objects" infrastructure is complaining that there was an
active timer freed by the 'vfree(counters);' in copy_entries_to_user(), via
IPT_SO_GET_ENTRIES.  But, 'counters' is simply an array of

	struct xt_counters {
		__u64 pcnt, bcnt;                       /* Packet and byte counters */
	};

There's no timer it can be freeing.

So I'm invalidating this report, as it probably was a weird bug elsewhere in the
kernel that has been fixed by now.

#syz invalid

- Eric