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From:   Yanjun Zhu <yanjunz@mellanox.com>
To:     Jason Gunthorpe <jgg@mellanox.com>,
        syzbot <syzbot+e11efb687f5ab7f01f3d@syzkaller.appspotmail.com>
CC:     "dledford@redhat.com" <dledford@redhat.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>,
        Moni Shoua <monis@mellanox.com>,
        "syzkaller-bugs@googlegroups.com" <syzkaller-bugs@googlegroups.com>
Subject: RE: KASAN: use-after-free Read in rxe_query_port
Thread-Topic: KASAN: use-after-free Read in rxe_query_port
Thread-Index: AQHV9jkJCU28FFAXfky+bua200OhVqhBGZPg
Date:   Tue, 10 Mar 2020 02:43:51 +0000
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Hi, Jason

I checked the source code and the symptoms.
1. In dmesg " rdma_rxe: ignoring netdev event =3D 10 for netdevsim0 ", this=
 indicates that the NIC which the rxe is based on is set to down.
Then the following will run:
"
ib_unregister_work
    __ib_unregister_device
        disable_device
            remove_client_context
                kfree
"
Finally the port is freed.
2. Cocurrently this port is accessed by the function=20
"
ib_query_port
    __ib_query_port
        rxe_query_port
"
So the use-after-free problem occurs.

Please comment.

Thanks a lot.
Zhu Yanjun

-----Original Message-----
From: Jason Gunthorpe <jgg@mellanox.com>=20
Sent: Tuesday, March 10, 2020 1:35 AM
To: syzbot <syzbot+e11efb687f5ab7f01f3d@syzkaller.appspotmail.com>
Cc: dledford@redhat.com; linux-kernel@vger.kernel.org; linux-rdma@vger.kern=
el.org; Moni Shoua <monis@mellanox.com>; syzkaller-bugs@googlegroups.com; Y=
anjun Zhu <yanjunz@mellanox.com>
Subject: Re: KASAN: use-after-free Read in rxe_query_port

On Sun, Mar 01, 2020 at 03:20:12AM -0800, syzbot wrote:
> Hello,
>=20
> syzbot found the following crash on:
>=20
> HEAD commit:    f8788d86 Linux 5.6-rc3
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=3D132d3645e0000=
0
> kernel config:  https://syzkaller.appspot.com/x/.config?x=3D9833e26bab355=
358
> dashboard link: https://syzkaller.appspot.com/bug?extid=3De11efb687f5ab7f=
01f3d
> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
>=20
> Unfortunately, I don't have any reproducer for this crash yet.
>=20
> IMPORTANT: if you fix the bug, please add the following tag to the commit=
:
> Reported-by: syzbot+e11efb687f5ab7f01f3d@syzkaller.appspotmail.com

Yanjun, do you have some idea what this could be?

Thanks,
Jason