Re: WARNING: kobject bug in br_add_if

[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+de73361ee4971b6e6f75@xxxxxxxxxxxxxxxxxxxxxxxxx> 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+de73361ee4971b6e6f75@xxxxxxxxxxxxxxxxxxxxxxxxx
> > 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
> 
> > ------------[ 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..