Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <00000000000037341d05fc460fa6@google.com>
In-Reply-To: <00000000000037341d05fc460fa6@google.com>
From:   Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date:   Mon, 22 May 2023 10:52:49 -0400
Message-ID: <CAF=yD-JpUc3SLtd7MtULmKOcERf6EJZ0rPc7WmJB2nUNUQRBjA@mail.gmail.com>
Subject: Re: [syzbot] [net?] KASAN: invalid-access Read in __packet_get_status
To:     syzbot <syzbot+64b0f633159fde08e1f1@syzkaller.appspotmail.com>
Cc:     bpf@vger.kernel.org, davem@davemloft.net, edumazet@google.com,
        kuba@kernel.org, linux-kernel@vger.kernel.org,
        netdev@vger.kernel.org, pabeni@redhat.com,
        syzkaller-bugs@googlegroups.com
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Mon, May 22, 2023 at 6:51=E2=80=AFAM syzbot
<syzbot+64b0f633159fde08e1f1@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    2d1bcbc6cd70 Merge tag 'probes-fixes-v6.4-rc1' of git://g=
i..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=3D154b8fa128000=
0
> kernel config:  https://syzkaller.appspot.com/x/.config?x=3D51dd28037b2a5=
5f
> dashboard link: https://syzkaller.appspot.com/bug?extid=3D64b0f633159fde0=
8e1f1
> compiler:       aarch64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110, =
GNU ld (GNU Binutils for Debian) 2.35.2
> userspace arch: arm64
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=3D12b6382e280=
000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=3D17fd0aee28000=
0
>
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/3=
84ffdcca292/non_bootable_disk-2d1bcbc6.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/d2e21a43e11e/vmlinu=
x-2d1bcbc6.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/49e0b029f9af/I=
mage-2d1bcbc6.gz.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the comm=
it:
> Reported-by: syzbot+64b0f633159fde08e1f1@syzkaller.appspotmail.com
>
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> BUG: KASAN: invalid-access in __packet_get_status+0x70/0xe0 net/packet/af=
_packet.c:438

The offending line is the last one in

"
static int __packet_get_status(const struct packet_sock *po, void *frame)
{
        union tpacket_uhdr h;

        smp_rmb();

        h.raw =3D frame;
        switch (po->tp_version) {
        case TPACKET_V1:
                flush_dcache_page(pgv_to_page(&h.h1->tp_status));
                return h.h1->tp_status;
        case TPACKET_V2:
                flush_dcache_page(pgv_to_page(&h.h2->tp_status));
"

The reproducer is very small:

"
// socket(PF_PACKET, SOCK_DGRAM, htons(ETH_P_ALL);
r0 =3D socket$packet(0x11, 0x2, 0x300)

// setsockopt PACKET_RX_RING with same block and frame sizes and counts
setsockopt$packet_rx_ring(r0, 0x107, 0x5,
&(0x7f0000000040)=3D@req3=3D{0x8000, 0x200, 0x80, 0x20000}, 0x1c)

// excessive length, too many bits in prot, MAP_SHARED | MAP_ANONYMOUS
mmap(&(0x7f0000568000/0x2000)=3Dnil, 0x1000000, 0x20567fff, 0x11, r0, 0x0)
"

What is odd here is that the program never sets packet version
explicitly, and the default is TPACKET_V1.