linux-kernel - Re: [syzbot] KASAN: vmalloc-out-of-bounds Read in bpf_jit

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Message-ID: <CANp29Y64wUeARFUn8Z0fjk7duxaZ3bJM2uGuVug_0ZmhGG_UTA@mail.gmail.com>
Date:   Wed, 16 Feb 2022 10:38:24 +0100
From:   Aleksandr Nogikh <nogikh@...gle.com>
To:     Song Liu <song@...nel.org>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        syzbot <syzbot+2f649ec6d2eea1495a8f@...kaller.appspotmail.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Martin KaFai Lau <kafai@...com>,
        KP Singh <kpsingh@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        open list <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Song Liu <songliubraving@...com>,
        syzkaller-bugs@...glegroups.com, Yonghong Song <yhs@...com>
Subject: Re: [syzbot] KASAN: vmalloc-out-of-bounds Read in bpf_jit_free

Hi Song,

Is syzkaller not doing something you expect it to do with this config?

On Wed, Feb 16, 2022 at 2:38 AM Song Liu <song@...nel.org> wrote:
>
> On Mon, Feb 14, 2022 at 10:41 PM Song Liu <song@...nel.org> wrote:
> >
> > On Mon, Feb 14, 2022 at 3:52 PM Daniel Borkmann <daniel@...earbox.net> wrote:
> > >
> > > Song, ptal.
> > >
> > > On 2/14/22 7:45 PM, syzbot wrote:
> > > > Hello,
> > > >
> > > > syzbot found the following issue on:
> > > >
> > > > HEAD commit:    e5313968c41b Merge branch 'Split bpf_sk_lookup remote_port..
> > > > git tree:       bpf-next
> > > > console output: https://syzkaller.appspot.com/x/log.txt?x=10baced8700000
> > > > kernel config:  https://syzkaller.appspot.com/x/.config?x=c40b67275bfe2a58
> > > > dashboard link: https://syzkaller.appspot.com/bug?extid=2f649ec6d2eea1495a8f
>
> How do I run the exact same syzkaller? I am doing something like
>
> ./bin/syz-manager -config qemu.cfg
>
> with the cfg file like:
>
> {
>         "target": "linux/amd64",
>         "http": ":56741",
>         "workdir": "workdir",
>         "kernel_obj": "linux",
>         "image": "./pkg/mgrconfig/testdata/stretch.img",

This image location looks suspicious - we store some dummy data for
tests in that folder.
Instances now run on buildroot-based images, generated with
https://github.com/google/syzkaller/blob/master/tools/create-buildroot-image.sh

>         "syzkaller": ".",
>         "disable_syscalls": ["keyctl", "add_key", "request_key"],

For our bpf instances, instead of disable_syscalls we use enable_syscalls:

"enable_syscalls": [
"bpf", "mkdir", "mount$bpf", "unlink", "close",
"perf_event_open*", "ioctl$PERF*", "getpid", "gettid",
"socketpair", "sendmsg", "recvmsg", "setsockopt$sock_attach_bpf",
"socket$kcm", "ioctl$sock_kcm*", "syz_clone",
"mkdirat$cgroup*", "openat$cgroup*", "write$cgroup*",
"openat$tun", "write$tun", "ioctl$TUN*", "ioctl$SIOCSIFHWADDR",
"openat$ppp", "syz_open_procfs$namespace"
]

>         "suppressions": ["some known bug"],
>         "procs": 8,

We usually run with "procs": 6, but it's not that important.

>         "type": "qemu",
>         "vm": {
>                 "count": 16,
>                 "cpu": 2,
>                 "mem": 2048,
>                 "kernel": "linux/arch/x86/boot/bzImage"
>         }
> }

Otherwise I don't see any really significant differences.

--
Best Regards
Aleksandr

>
> Is this correct? I am using stretch.img from syzkaller site, and the
> .config from
> the link above.
>
> Thanks,
> Song
>