Re: [syzbot] WARNING: refcount bug in nldev_newlink

[Guoqing Jiang <guoqing.jiang@linux.dev>]

Hi,

On 12/8/22 5:14 PM, Leon Romanovsky wrote:
> On Wed, Dec 07, 2022 at 12:51:39PM -0800, syzbot wrote:
>> Hello,
>>
>> syzbot found the following issue on:
>>
>> HEAD commit:    591cd61541b9 Add linux-next specific files for 20221207
>> git tree:       linux-next
>> console+strace: https://syzkaller.appspot.com/x/log.txt?x=11aeafad880000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=8b2d3e63e054c24f
>> dashboard link: https://syzkaller.appspot.com/bug?extid=3fd8326d9a0812d19218
>> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=112536fb880000
>> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16aa2e6d880000
>>
>> Downloadable assets:
>> disk image: https://storage.googleapis.com/syzbot-assets/bc862c01ec56/disk-591cd615.raw.xz
>> vmlinux: https://storage.googleapis.com/syzbot-assets/8f9b93f8ed2f/vmlinux-591cd615.xz
>> kernel image: https://storage.googleapis.com/syzbot-assets/9d5cb636d548/bzImage-591cd615.xz
>>
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+3fd8326d9a0812d19218@syzkaller.appspotmail.com
>>
>> WARNING: CPU: 0 PID: 5156 at lib/refcount.c:31 refcount_warn_saturate+0x1d7/0x1f0 lib/refcount.c:31
>> Modules linked in:
>> CPU: 0 PID: 5156 Comm: syz-executor773 Not tainted 6.1.0-rc8-next-20221207-syzkaller #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022
>> RIP: 0010:refcount_warn_saturate+0x1d7/0x1f0 lib/refcount.c:31
>> Code: 05 5a 60 51 0a 01 e8 35 0a b5 05 0f 0b e9 d3 fe ff ff e8 6c 9b 75 fd 48 c7 c7 c0 6d a6 8a c6 05 37 60 51 0a 01 e8 16 0a b5 05 <0f> 0b e9 b4 fe ff ff 48 89 ef e8 5a b5 c3 fd e9 5c fe ff ff 0f 1f
>> RSP: 0018:ffffc90003ebf0d8 EFLAGS: 00010286
>> RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
>> RDX: ffff88802bfcba80 RSI: ffffffff8166b1dc RDI: fffff520007d7e0d
>> RBP: ffff888070296600 R08: 0000000000000005 R09: 0000000000000000
>> R10: 0000000080000000 R11: 0000000000000000 R12: 1ffff920007d7e20
>> R13: 0000000000000000 R14: ffff888070296600 R15: ffffc90003ebf608
>> FS:  000055555600f300(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007ffed185b004 CR3: 00000000265db000 CR4: 00000000003506f0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>>   <TASK>
>>   __refcount_dec include/linux/refcount.h:344 [inline]
>>   refcount_dec include/linux/refcount.h:359 [inline]
>>   ref_tracker_free+0x539/0x6b0 lib/ref_tracker.c:118
>>   netdev_tracker_free include/linux/netdevice.h:4039 [inline]
>>   netdev_put include/linux/netdevice.h:4056 [inline]
>>   dev_put include/linux/netdevice.h:4082 [inline]
>>   nldev_newlink+0x360/0x5d0 drivers/infiniband/core/nldev.c:1733
>>   rdma_nl_rcv_msg+0x371/0x6a0 drivers/infiniband/core/netlink.c:195
>>   rdma_nl_rcv_skb.constprop.0.isra.0+0x2fc/0x440 drivers/infiniband/core/netlink.c:239
>>   netlink_unicast_kernel net/netlink/af_netlink.c:1330 [inline]
>>   netlink_unicast+0x547/0x7f0 net/netlink/af_netlink.c:1356
>>   netlink_sendmsg+0x91b/0xe10 net/netlink/af_netlink.c:1932
>>   sock_sendmsg_nosec net/socket.c:714 [inline]
>>   sock_sendmsg+0xd3/0x120 net/socket.c:734
>>   ____sys_sendmsg+0x712/0x8c0 net/socket.c:2476
>>   ___sys_sendmsg+0x110/0x1b0 net/socket.c:2530
>>   __sys_sendmsg+0xf7/0x1c0 net/socket.c:2559
>>   do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>>   do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
>>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
>> RIP: 0033:0x7fd5bc473699
>> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 41 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
>> RSP: 002b:00007ffed185aff8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
>> RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fd5bc473699
>> RDX: 0000000000000000 RSI: 0000000020000340 RDI: 0000000000000003
>> RBP: 0000000000000000 R08: 000000000000000d R09: 000000000000000d
>> R10: 00007ffed185aa70 R11: 0000000000000246 R12: 00007ffed185b010
>> R13: 00000000000f4240 R14: 0000000000011fc1 R15: 00007ffed185b004
>>   </TASK>
>>
>>
>> ---
>> This report is generated by a bot. It may contain errors.
>> See https://goo.gl/tpsmEJ for more information about syzbot.
>> syzbot engineers can be reached at syzkaller@googlegroups.com.
>>
>> syzbot will keep track of this issue. See:
>> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>> syzbot can test patches for this issue, for details see:
>> https://goo.gl/tpsmEJ#testing-patches
> Jason, what do you think?
>
> diff --git a/drivers/infiniband/core/nldev.c b/drivers/infiniband/core/nldev.c
> index a981ac2f0975..982938c1dae3 100644
> --- a/drivers/infiniband/core/nldev.c
> +++ b/drivers/infiniband/core/nldev.c
> @@ -1730,7 +1730,8 @@ static int nldev_newlink(struct sk_buff *skb, struct nlmsghdr *nlh,
>   #endif
>          err = ops ? ops->newlink(ibdev_name, ndev) : -EINVAL;
>          up_read(&link_ops_rwsem);
> -       dev_put(ndev);
> +       if (err)
> +               dev_put(ndev);
>   
>          return err;
>   }
>

I guess the dev_put is paired with dev_hold in dev_get_by_name,
maybe it should be protected by ink_ops_rwsem, otherwise
siw_exit_module could call  ib_unregister_driver -> free_netdevs
after rdma_link_unregister (which needs to hold link_ops_rwsem),
then seems it is possible that ndev is freed before nldev_newlink
calls dev_put.

diff --git a/drivers/infiniband/core/nldev.c 
b/drivers/infiniband/core/nldev.c
index 12dc97067ed2..f49bc8ee46da 100644
--- a/drivers/infiniband/core/nldev.c
+++ b/drivers/infiniband/core/nldev.c
@@ -1715,8 +1715,8 @@ static int nldev_newlink(struct sk_buff *skb, 
struct nlmsghdr *nlh,
         }
  #endif
         err = ops ? ops->newlink(ibdev_name, ndev) : -EINVAL;
-       up_read(&link_ops_rwsem);
         dev_put(ndev);
+       up_read(&link_ops_rwsem);

         return err;
  }

Thanks,
Guoqing