Re: WARNING in bpf_cgroup_link_release

From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Andrii Nakryiko <andriin@fb.com>,
	Daniel Borkmann <daniel@iogearbox.net>,
	syzbot <syzbot+8a5dadc5c0b1d7055945@syzkaller.appspotmail.com>,
	Alexei Starovoitov <ast@kernel.org>, bpf <bpf@vger.kernel.org>,
	john fastabend <john.fastabend@gmail.com>,
	Martin Lau <kafai@fb.com>, KP Singh <kpsingh@chromium.org>,
	open list <linux-kernel@vger.kernel.org>,
	Networking <netdev@vger.kernel.org>,
	Song Liu <songliubraving@fb.com>,
	syzkaller-bugs@googlegroups.com, Yonghong Song <yhs@fb.com>
Subject: Re: WARNING in bpf_cgroup_link_release
Date: Thu, 16 Apr 2020 12:47:25 -0700	[thread overview]
Message-ID: <CAEf4BzY2XwQw0ZMN6PaJtN=DfAMQyMtGuo7dnmVH1embBXmhuw@mail.gmail.com> (raw)
In-Reply-To: <20200416102612.GO1163@kadam>

On Thu, Apr 16, 2020 at 3:29 AM Dan Carpenter <dan.carpenter@oracle.com> wrote:
>
> On Wed, Apr 15, 2020 at 09:51:40AM -0700, 'Andrii Nakryiko' via syzkaller-bugs wrote:
> > On 4/15/20 4:57 AM, Daniel Borkmann wrote:
> > > On 4/15/20 8:55 AM, syzbot wrote:
> > > > Hello,
> > > >
> > > > syzbot found the following crash on:
> > >
> > > Andrii, ptal.
> > >
> > > > HEAD commit:    1a323ea5 x86: get rid of 'errret' argument to
> > > > __get_user_x..
> > > > git tree:       bpf-next
> > > > console output: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_log.txt-3Fx-3D148ccb57e00000&d=DwICaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=vxqvl81C2rT6GOGdPyz8iQ&m=T2Ez0XmyIpHmEa_MPTTUOh61jMDXqwETtTaTbSe-2M4&s=-6XBbsNV1O4X5flrx4Yssfjc56d0qeSHgwHhd92UPJc&e=
> > > > kernel config:  https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_x_.config-3Fx-3D8c1e98458335a7d1&d=DwICaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=vxqvl81C2rT6GOGdPyz8iQ&m=T2Ez0XmyIpHmEa_MPTTUOh61jMDXqwETtTaTbSe-2M4&s=s5-1AlWtSiBvo66WN4_UXoXMGIGIqsoUCrmAnxNnfX0&e=
> > > > dashboard link: https://urldefense.proofpoint.com/v2/url?u=https-3A__syzkaller.appspot.com_bug-3Fextid-3D8a5dadc5c0b1d7055945&d=DwICaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=vxqvl81C2rT6GOGdPyz8iQ&m=T2Ez0XmyIpHmEa_MPTTUOh61jMDXqwETtTaTbSe-2M4&s=hAA0702qJH5EwRwvG0RKmj8FwIRm1O8hvmoS7ne5Dls&e=
> > > > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > > >
> > > > Unfortunately, I don't have any reproducer for this crash yet.
> > > >
> > > > IMPORTANT: if you fix the bug, please add the following tag to the
> > > > commit:
> > > > Reported-by: syzbot+8a5dadc5c0b1d7055945@syzkaller.appspotmail.com
> > > >
> > > > ------------[ cut here ]------------
> > > > WARNING: CPU: 0 PID: 25081 at kernel/bpf/cgroup.c:796
> > > > bpf_cgroup_link_release+0x260/0x3a0 kernel/bpf/cgroup.c:796
> >
> > This warning is triggered due to __cgroup_bpf_detach returning an error. It
> > can do it only in two cases: either attached item is not found, which from
> > starting at code some moreI don't see how that can happen. The other reason
> > - kmalloc() failing to allocate memory for new effective prog array.
>
> If you look at the log file then this was allocation fault injection in
> bpf_prog_array_alloc().

Ah, I see, thanks for pointing this out! So that confirms that it's
not a bug, but just unfortunate result of potentially failing cgroup
BPF program detach code path.

>
> https://syzkaller.appspot.com/x/log.txt?x=148ccb57e00000
>
> regards,
> dan carpenter
>