netdev - Re: [syzbot] [net?] KASAN: invalid-access Read in __packet_get

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Date: Mon, 22 May 2023 10:52:49 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: syzbot <syzbot+64b0f633159fde08e1f1@...kaller.appspotmail.com>
Cc: bpf@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com, 
	kuba@...nel.org, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, 
	pabeni@...hat.com, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [net?] KASAN: invalid-access Read in __packet_get_status

On Mon, May 22, 2023 at 6:51 AM syzbot
<syzbot+64b0f633159fde08e1f1@...kaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    2d1bcbc6cd70 Merge tag 'probes-fixes-v6.4-rc1' of git://gi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=154b8fa1280000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=51dd28037b2a55f
> dashboard link: https://syzkaller.appspot.com/bug?extid=64b0f633159fde08e1f1
> 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=12b6382e280000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17fd0aee280000
>
> Downloadable assets:
> disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/384ffdcca292/non_bootable_disk-2d1bcbc6.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/d2e21a43e11e/vmlinux-2d1bcbc6.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/49e0b029f9af/Image-2d1bcbc6.gz.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+64b0f633159fde08e1f1@...kaller.appspotmail.com
>
> ==================================================================
> 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 = 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 = 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)=@...3={0x8000, 0x200, 0x80, 0x20000}, 0x1c)

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

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