WARNING: kobject bug in br_add_if

[syzbot]

Hello,

syzbot hit the following crash on upstream commit
10b84daddbec72c6b440216a69de9a9605127f7a (Sat Mar 31 17:59:00 2018 +0000)
Merge branch 'perf-urgent-for-linus' of
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
syzbot dashboard link:
https://syzkaller.appspot.com/bug?extid=de73361ee4971b6e6f75

So far this crash happened 4 times on net-next, upstream.
Unfortunately, I don't have any reproducer for this crash yet.
Raw console output:
https://syzkaller.appspot.com/x/log.txt?id=5007286875455488
Kernel config:
https://syzkaller.appspot.com/x/.config?id=-2760467897697295172
compiler: gcc (GCC) 7.1.1 20170620

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+de7336...@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.

R13: 0000000000000369 R14: 00000000006f7278 R15: 0000000000000006
------------[ cut here ]------------
binder: 23650:23651 unknown command 1078223622
kobject_add_internal failed for brport (error: -12 parent: bond0)
binder: 23650:23651 ioctl c0306201 2000dfd0 returned -22
WARNING: CPU: 1 PID: 23647 at lib/kobject.c:242
kobject_add_internal+0x3f6/0xbc0 lib/kobject.c:240
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 23647 Comm: syz-executor7 Not tainted 4.16.0-rc7+ #374
binder: BINDER_SET_CONTEXT_MGR already set
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+0x1f4/0x2b0 lib/bug.c:186
fixup_bug.part.10+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+0x1b/0x40 arch/x86/entry/entry_64.S:986
RIP: 0010:kobject_add_internal+0x3f6/0xbc0 lib/kobject.c:240
RSP: 0018:ffff8801d089f560 EFLAGS: 00010286
RAX: dffffc0000000008 RBX: ffff8801adbee178 RCX: ffffffff815b193e
RDX: 0000000000040000 RSI: ffffc900022aa000 RDI: 1ffff1003a113e31
RBP: ffff8801d089f658 R08: 1ffff1003a113df3 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 1ffff1003a113eb2
R13: 00000000fffffff4 R14: ffff8801abd88828 R15: ffff8801d75a1e00
kobject_add_varg lib/kobject.c:364 [inline]
kobject_init_and_add+0xf9/0x150 lib/kobject.c:436
br_add_if+0x79a/0x1a70 net/bridge/br_if.c:533
add_del_if+0xf4/0x140 net/bridge/br_ioctl.c:101
br_dev_ioctl+0xa2/0xc0 net/bridge/br_ioctl.c:396
dev_ifsioc+0x333/0x9b0 net/core/dev_ioctl.c:334
dev_ioctl+0x176/0xbe0 net/core/dev_ioctl.c:500
sock_do_ioctl+0x1ba/0x390 net/socket.c:981
sock_ioctl+0x367/0x670 net/socket.c:1081
vfs_ioctl fs/ioctl.c:46 [inline]
do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:686
SYSC_ioctl fs/ioctl.c:701 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:692
do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287
entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x454e79
RSP: 002b:00007eff7dab7c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007eff7dab86d4 RCX: 0000000000454e79
RDX: 0000000020000000 RSI: 00000000000089a2 RDI: 0000000000000014
RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000015
R13: 0000000000000369 R14: 00000000006f7278 R15: 0000000000000006
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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[Dmitry Vyukov]

On Wed, Apr 11, 2018 at 5:15 PM, syzbot
<syzbot+de7336...@syzkaller.appspotmail.com> wrote:
> Hello,
>
> syzbot hit the following crash on upstream commit
> 10b84daddbec72c6b440216a69de9a9605127f7a (Sat Mar 31 17:59:00 2018 +0000)
> Merge branch 'perf-urgent-for-linus' of
> git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
> syzbot dashboard link:
> https://syzkaller.appspot.com/bug?extid=de73361ee4971b6e6f75
>
> So far this crash happened 4 times on net-next, upstream.
> Unfortunately, I don't have any reproducer for this crash yet.
> Raw console output:
> https://syzkaller.appspot.com/x/log.txt?id=5007286875455488
> Kernel config:
> https://syzkaller.appspot.com/x/.config?id=-2760467897697295172
> compiler: gcc (GCC) 7.1.1 20170620
>
> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> Reported-by: syzbot+de7336...@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.

+Greg

The plan is to remove this WARNING from kobject_add, if there are no objections.

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[Hangbin Liu]

On Wed, Apr 11, 2018 at 05:18:23PM +0200, Dmitry Vyukov wrote:
> On Wed, Apr 11, 2018 at 5:15 PM, syzbot
> <syzbot+de7336...@syzkaller.appspotmail.com> wrote:
> > Hello,
> >
> > syzbot hit the following crash on upstream commit
> > 10b84daddbec72c6b440216a69de9a9605127f7a (Sat Mar 31 17:59:00 2018 +0000)
> > Merge branch 'perf-urgent-for-linus' of
> > git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
> > syzbot dashboard link:
> > https://syzkaller.appspot.com/bug?extid=de73361ee4971b6e6f75
> >
> > So far this crash happened 4 times on net-next, upstream.
> > Unfortunately, I don't have any reproducer for this crash yet.
> > Raw console output:
> > https://syzkaller.appspot.com/x/log.txt?id=5007286875455488
> > Kernel config:
> > https://syzkaller.appspot.com/x/.config?id=-2760467897697295172
> > compiler: gcc (GCC) 7.1.1 20170620
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+de7336...@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.
>
> +Greg
>
> The plan is to remove this WARNING from kobject_add, if there are no objections.

Hi Dmitry,

For this bug, why should we remove the WARNING instead of adding a check in
br_add_if()? Something like

diff --git a/net/bridge/br_if.c b/net/bridge/br_if.c
index 82c1a6f..79dcc3d 100644
--- a/net/bridge/br_if.c
+++ b/net/bridge/br_if.c
@@ -518,8 +518,8 @@ int br_add_if(struct net_bridge *br, struct net_device *dev,
return -ELOOP;
}

- /* Device is already being bridged */
- if (br_port_exists(dev))
+ /* Device still has master upper dev */
+ if (netdev_master_upper_dev_get(dev))
return -EBUSY;

/* No bridging devices that dislike that (e.g. wireless) */

Thanks
Hangbin

[Dmitry Vyukov]

Mainline because nobody wants to fix these.
If you think this is a real bug and you are ready to fix it, please
mail an official patch.

[Hangbin Liu]

> >> > ------------[ cut here ]------------
> >> > binder: 23650:23651 unknown command 1078223622
> >> > kobject_add_internal failed for brport (error: -12 parent: bond0)

Re-checked the error. This is a -ENOMEM. So normally we could ignore it.

But on the other hand, although we could find out the slave iface's
master in netdev_master_upper_dev_link(). It already go much further
and allocate some resource and change iface state. e.g.

[54273.968516] br0: port 1(em1) entered blocking state
[54273.973979] br0: port 1(em1) entered disabled state

So I think we'd better return as early as possible. I will post a fix
for this.

Thanks
Hangbin

[Nikolay Aleksandrov]

On 26/04/18 13:37, Hangbin Liu wrote:
> On Thu, Apr 26, 2018 at 10:04:16AM +0200, Dmitry Vyukov wrote:
>> On Thu, Apr 26, 2018 at 8:13 AM, Hangbin Liu <liuha...@gmail.com> wrote:
>>> On Wed, Apr 11, 2018 at 05:18:23PM +0200, Dmitry Vyukov wrote:
>>>> On Wed, Apr 11, 2018 at 5:15 PM, syzbot
>>>> <syzbot+de7336...@syzkaller.appspotmail.com> wrote:
>>>>> kobject_add_internal failed for brport (error: -12 parent: bond0)

[snip]

>
> Re-checked the error. This is a -ENOMEM. So normally we could ignore it.
>
> But on the other hand, although we could find out the slave iface's
> master in netdev_master_upper_dev_link(). It already go much further
> and allocate some resource and change iface state. e.g.
>
> [54273.968516] br0: port 1(em1) entered blocking state
> [54273.973979] br0: port 1(em1) entered disabled state
>
> So I think we'd better return as early as possible. I will post a fix
> for this.
>
> Thanks
> Hangbin

If I'm not mistaken the bridge allocated resources for the port are
cleaned on kobject_init_and_add() error return. Or are you talking
about some other resources ?

[Nikolay Aleksandrov]

Ah, my bad - you weren't talking about resource freeing.
Nevermind my comment.