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From:   Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Date:   Mon, 22 May 2023 12:19:41 -0400
Message-ID: <CAF=yD-+MxyoD1Mbekf93-XhAA2urAf5audD8HefmF8bfsu51iQ@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,
        linux-arm-kernel@lists.infradead.org
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On Mon, May 22, 2023 at 10:52=E2=80=AFAM Willem de Bruijn
<willemdebruijn.kernel@gmail.com> wrote:
>
> 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:/=
/gi..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=3D154b8fa1280=
000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=3D51dd28037b2=
a55f
> > dashboard link: https://syzkaller.appspot.com/bug?extid=3D64b0f633159fd=
e08e1f1
> > 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=3D12b6382e2=
80000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=3D17fd0aee280=
000
> >
> > 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/vmli=
nux-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 co=
mmit:
> > 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.

The test is marked as repeat.

One possibility is that there is a race between packet arrival calling
flush_dcache_page and user mmap setup/teardown. That would exhibit as
flakiness.

ARM flush_dcache_page is quite outside my networking comfort zone.