WARNING in __proc_create

[syzbot]

Hello,

syzbot hit the following crash on net-next commit
617aebe6a97efa539cc4b8a52adccd89596e6be0 (Sun Feb 4 00:25:42 2018 +0000)
Merge tag 'usercopy-v4.16-rc1' of
git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

So far this crash happened 12 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: syzbot+0502b0...@syzkaller.appspotmail.com
It will help syzbot understand when the bug is fixed. See footer for
details.
If you forward the report, please keep this part and the footer.

audit: type=1400 audit(1518223777.419:7): avc: denied { map } for
pid=4159 comm="syzkaller598581" path="/root/syzkaller598581546" dev="sda1"
ino=16481 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023
tcontext=unconfined_u:object_r:user_home_t:s0 tclass=file permissive=1
------------[ cut here ]------------
name len 0
WARNING: CPU: 0 PID: 4159 at fs/proc/generic.c:354
__proc_create+0x696/0x880 fs/proc/generic.c:354
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 4159 Comm: syzkaller598581 Not tainted 4.15.0+ #221
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
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+0x22/0x40 arch/x86/entry/entry_64.S:1097
RIP: 0010:__proc_create+0x696/0x880 fs/proc/generic.c:354
RSP: 0018:ffff8801d3167418 EFLAGS: 00010282
RAX: dffffc0000000008 RBX: 1ffff1003a62ce88 RCX: ffffffff815a57ae
RDX: 0000000000000000 RSI: 1ffff1003a62ce33 RDI: 1ffff1003a62ce08
RBP: ffff8801d3167588 R08: 1ffff1003a62cdca R09: 0000000000000000
R10: ffff8801d31672d0 R11: 0000000000000000 R12: ffff8801b1ee9a70
R13: ffff8801d3167560 R14: 0000000000000000 R15: ffff8801d3167520
proc_create_data+0x76/0x180 fs/proc/generic.c:488
htable_create net/netfilter/xt_hashlimit.c:333 [inline]
hashlimit_mt_check_common.isra.9+0xaee/0x1420
net/netfilter/xt_hashlimit.c:900
hashlimit_mt_check_v1+0x48d/0x640 net/netfilter/xt_hashlimit.c:926
xt_check_match+0x231/0x7d0 net/netfilter/x_tables.c:470
check_match net/ipv6/netfilter/ip6_tables.c:492 [inline]
find_check_match net/ipv6/netfilter/ip6_tables.c:509 [inline]
find_check_entry.isra.7+0x42d/0xcf0 net/ipv6/netfilter/ip6_tables.c:560
translate_table+0xf52/0x1690 net/ipv6/netfilter/ip6_tables.c:744
do_replace net/ipv6/netfilter/ip6_tables.c:1160 [inline]
do_ip6t_set_ctl+0x370/0x5f0 net/ipv6/netfilter/ip6_tables.c:1686
nf_sockopt net/netfilter/nf_sockopt.c:106 [inline]
nf_setsockopt+0x67/0xc0 net/netfilter/nf_sockopt.c:115
ipv6_setsockopt+0x10b/0x130 net/ipv6/ipv6_sockglue.c:927
rawv6_setsockopt+0x4a/0xf0 net/ipv6/raw.c:1060
sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2975
SYSC_setsockopt net/socket.c:1849 [inline]
SyS_setsockopt+0x189/0x360 net/socket.c:1828
entry_SYSCALL_64_fastpath+0x29/0xa0
RIP: 0033:0x441319
RSP: 002b:00007ffde3898248 EFLAGS: 00000203 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: ffffffffffffffff RCX: 0000000000441319
RDX: 0000000000000040 RSI: 0000000000000029 RDI: 0000000000000003
RBP: 00000000006cb018 R08: 00000000000005c8 R09: 0000000000000000
R10: 0000000020ee3a38 R11: 0000000000000203 R12: 0000000000402c40
R13: 0000000000402cd0 R14: 0000000000000000 R15: 0000000000000000
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
This bug is generated by a dumb bot. It may contain errors.
See https://goo.gl/tpsmEJ for details.
Direct all questions to syzk...@googlegroups.com.

syzbot will keep track of this bug report.
If you forgot to add the Reported-by tag, once the fix for this bug is
merged
into any tree, please reply to this email with:
#syz fix: exact-commit-title
If you want to test a patch for this bug, please reply with:
#syz test: git://repo/address.git branch
and provide the patch inline or as an attachment.
To mark this as a duplicate of another syzbot report, please reply with:
#syz dup: exact-subject-of-another-report
If it's a one-off invalid bug report, please reply with:
#syz invalid
Note: if the crash happens again, it will cause creation of a new bug
report.
Note: all commands must start from beginning of the line in the email body.

[Cong Wang]

We need to reject empty names.

[Eric Dumazet]

I sent a patch a while back, but Pablo/Florian wanted more than that
simple fix.

We also need to filter special characters like '/'

Or maybe I am mixing with something else.

[Eric Dumazet]

On 03/09/2018 02:56 PM, Eric Dumazet wrote:

>
> I sent a patch a while back, but Pablo/Florian wanted more than that
> simple fix.
>
> We also need to filter special characters like '/'
>
> Or maybe I am mixing with something else.

Yes, Florian mentioned that we also had to reject "." and ".."

[Florian Westphal]

Eric Dumazet <eric.d...@gmail.com> wrote:
> >>fs/proc/generic.c:354
> >
> >We need to reject empty names.
> >
>
> I sent a patch a while back, but Pablo/Florian wanted more than that simple
> fix.
>
> We also need to filter special characters like '/'
>
> Or maybe I am mixing with something else.

Argh, sorry, this fell off the truck it seems :(

I'll work on this tomorrow unless someone else does it today ;)

[Cong Wang]

On Fri, Mar 9, 2018 at 2:58 PM, Eric Dumazet <eric.d...@gmail.com> wrote:
>
>
> On 03/09/2018 02:56 PM, Eric Dumazet wrote:
>
>>
>> I sent a patch a while back, but Pablo/Florian wanted more than that
>> simple fix.
>>
>> We also need to filter special characters like '/'

proc_create_data() itself accepts '/', so it must be xt_hashlimit doesn't
want it.

>>
>> Or maybe I am mixing with something else.
>
>
> Yes, Florian mentioned that we also had to reject "." and ".."
>

It could be, but looks like not as trivial as just strstr(".")?

BTW, the warning itself is all about empty names, so perhaps
it's better to fix them separately.

[Florian Westphal]

Cong Wang <xiyou.w...@gmail.com> wrote:
> On Fri, Mar 9, 2018 at 2:58 PM, Eric Dumazet <eric.d...@gmail.com> wrote:
> >
> >
> > On 03/09/2018 02:56 PM, Eric Dumazet wrote:
> >
> >>
> >> I sent a patch a while back, but Pablo/Florian wanted more than that
> >> simple fix.
> >>
> >> We also need to filter special characters like '/'
>
> proc_create_data() itself accepts '/', so it must be xt_hashlimit doesn't
> want it.

--hashimit-name / also triggers WARN for me.
. or .. "work", (no crash), but cause appearance of 2nd ./.. in
/proc/net/ipt_hashlimit , so I think its better to disallow that too.