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Message-ID: <CACT4Y+bZb6_gBqzLMbHujwNgD-6b9qNvxyf0vgwDuHc3WYZ5xQ@mail.gmail.com>
Date: Mon, 17 May 2021 17:46:06 +0200
From: Dmitry Vyukov <dvyukov@...gle.com>
To: syzbot <syzbot+106457891e3cf3b273a9@...kaller.appspotmail.com>
Cc: Andrii Nakryiko <andrii@...nel.org>,
Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>,
Daniel Borkmann <daniel@...earbox.net>,
David Miller <davem@...emloft.net>,
Alexander Potapenko <glider@...gle.com>,
John Fastabend <john.fastabend@...il.com>,
Martin KaFai Lau <kafai@...com>,
KP Singh <kpsingh@...nel.org>,
Jakub Kicinski <kuba@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
netdev <netdev@...r.kernel.org>,
Song Liu <songliubraving@...com>,
syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
Tanner Love <tannerlove@...gle.com>,
Willem de Bruijn <willemdebruijn.kernel@...il.com>,
Xie He <xie.he.0141@...il.com>, Yonghong Song <yhs@...com>
Subject: Re: [syzbot] KMSAN: uninit-value in virtio_net_hdr_to_skb
On Mon, May 17, 2021 at 5:44 PM syzbot
<syzbot+106457891e3cf3b273a9@...kaller.appspotmail.com> wrote:
>
> > On Mon, May 17, 2021 at 5:13 PM Willem de Bruijn
> > <willemdebruijn.kernel@...il.com> wrote:
> >>
> >> On Mon, May 17, 2021 at 10:57 AM Dmitry Vyukov <dvyukov@...gle.com> wrote:
> >> >
> >> > On Mon, May 17, 2021 at 4:06 PM Willem de Bruijn
> >> > <willemdebruijn.kernel@...il.com> wrote:
> >> > >
> >> > > On Mon, May 17, 2021 at 7:27 AM syzbot
> >> > > <syzbot+106457891e3cf3b273a9@...kaller.appspotmail.com> wrote:
> >> > > >
> >> > > > Hello,
> >> > > >
> >> > > > syzbot found the following issue on:
> >> > > >
> >> > > > HEAD commit: 4ebaab5f kmsan: drop unneeded references to kmsan_context_..
> >> > > > git tree: https://github.com/google/kmsan.git master
> >> > > > console output: https://syzkaller.appspot.com/x/log.txt?x=17ac508ed00000
> >> > > > kernel config: https://syzkaller.appspot.com/x/.config?x=ab8076fe8508c0d3
> >> > > > dashboard link: https://syzkaller.appspot.com/bug?extid=106457891e3cf3b273a9
> >> > > > compiler: Debian clang version 11.0.1-2
> >> > > > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=138f4972d00000
> >> > > > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1624ffced00000
> >> > > >
> >> > > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> >> > > > Reported-by: syzbot+106457891e3cf3b273a9@...kaller.appspotmail.com
> >> > > >
> >> > > > =====================================================
> >> > > > BUG: KMSAN: uninit-value in virtio_net_hdr_to_skb+0x1414/0x14f0 include/linux/virtio_net.h:86
> >> > >
> >> > > No answer/fix, just initial investigation.
> >> > >
> >> > > This is an odd location. Line 86 is the inner if statement. Both
> >> > > protocol and skb->protocol are clearly initialized by then. But, that
> >> > > is also not the allocation that MSAN reports, see below.
> >> > >
> >> > > if (!skb->protocol) {
> >> > > __be16 protocol =
> >> > > dev_parse_header_protocol(skb);
> >> > >
> >> > > virtio_net_hdr_set_proto(skb, hdr);
> >> > > if (protocol && protocol != skb->protocol)
> >> > > return -EINVAL;
> >> > > }
> >> > >
> >> > > The repro itself seems mostly straightforward:
> >> > >
> >> > > - create a packet socket
> >> > > - enable PACKET_VNET_HDR with setsockopt(r3, 0x107, 0xf ..)
> >> > > - bind to AF_PACKET (0x11)
> >> > >
> >> > > - create a pipe
> >> > > - write to pipe[1]
> >> > > - splice pipe[0] to the packet socket
> >> > >
> >> > > there are a few other calls that I think are irrelevant and/or would fail.
> >> > >
> >> > > Perhaps there is some race condition in device refcounting, as bind
> >> > > operates on that?
> >> > >
> >> > > > CPU: 0 PID: 8426 Comm: syz-executor777 Not tainted 5.12.0-rc6-syzkaller #0
> >> > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> >> > > > Call Trace:
> >> > > > __dump_stack lib/dump_stack.c:79 [inline]
> >> > > > dump_stack+0x24c/0x2e0 lib/dump_stack.c:120
> >> > > > kmsan_report+0xfb/0x1e0 mm/kmsan/kmsan_report.c:118
> >> > > > __msan_warning+0x5c/0xa0 mm/kmsan/kmsan_instr.c:197
> >> > > > virtio_net_hdr_to_skb+0x1414/0x14f0 include/linux/virtio_net.h:86
> >> > > > packet_snd net/packet/af_packet.c:2994 [inline]
> >> > > > packet_sendmsg+0x85b8/0x99d0 net/packet/af_packet.c:3031
> >> > > > sock_sendmsg_nosec net/socket.c:654 [inline]
> >> > > > sock_sendmsg net/socket.c:674 [inline]
> >> > > > kernel_sendmsg+0x22c/0x2f0 net/socket.c:694
> >> > > > sock_no_sendpage+0x205/0x2b0 net/core/sock.c:2860
> >> > > > kernel_sendpage+0x47a/0x590 net/socket.c:3631
> >> > > > sock_sendpage+0x161/0x1a0 net/socket.c:947
> >> > > > pipe_to_sendpage+0x3e4/0x520 fs/splice.c:364
> >> > > > splice_from_pipe_feed fs/splice.c:418 [inline]
> >> > > > __splice_from_pipe+0x5e3/0xff0 fs/splice.c:562
> >> > > > splice_from_pipe fs/splice.c:597 [inline]
> >> > > > generic_splice_sendpage+0x1d5/0x2c0 fs/splice.c:746
> >> > > > do_splice_from fs/splice.c:767 [inline]
> >> > > > do_splice+0x23c3/0x2c10 fs/splice.c:1079
> >> > > > __do_splice fs/splice.c:1144 [inline]
> >> > > > __do_sys_splice fs/splice.c:1350 [inline]
> >> > > > __se_sys_splice+0x8fa/0xb50 fs/splice.c:1332
> >> > > > __x64_sys_splice+0x6e/0x90 fs/splice.c:1332
> >> > > > do_syscall_64+0x9f/0x140 arch/x86/entry/common.c:48
> >> > > > entry_SYSCALL_64_after_hwframe+0x44/0xae
> >> > > > RIP: 0033:0x449a39
> >> > > > Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 d1 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> >> > > > RSP: 002b:00007f8ed790b2f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
> >> > > > RAX: ffffffffffffffda RBX: 00000000004cf518 RCX: 0000000000449a39
> >> > > > RDX: 0000000000000005 RSI: 0000000000000000 RDI: 0000000000000003
> >> > > > RBP: 00000000004cf510 R08: 000000000004ffe0 R09: 0000000000000000
> >> > > > R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004cf51c
> >> > > > R13: 000000000049e46c R14: 6d32cc5e8ead0600 R15: 0000000000022000
> >> > > >
> >> > > > Uninit was created at:
> >> > > > kmsan_save_stack_with_flags+0x3c/0x90 mm/kmsan/kmsan.c:121
> >> > > > kmsan_alloc_page+0xd0/0x1e0 mm/kmsan/kmsan_shadow.c:274
> >> > > > __alloc_pages_nodemask+0x827/0xf90 mm/page_alloc.c:5044
> >> > > > alloc_pages_current+0x7b6/0xb60 mm/mempolicy.c:2277
> >> > > > alloc_pages include/linux/gfp.h:561 [inline]
> >> > > > alloc_slab_page mm/slub.c:1653 [inline]
> >> > > > allocate_slab+0x364/0x1260 mm/slub.c:1793
> >> > > > new_slab mm/slub.c:1856 [inline]
> >> > > > new_slab_objects mm/slub.c:2602 [inline]
> >> > > > ___slab_alloc+0xd42/0x1930 mm/slub.c:2765
> >> > > > __slab_alloc mm/slub.c:2805 [inline]
> >> > > > slab_alloc_node mm/slub.c:2886 [inline]
> >> > > > slab_alloc mm/slub.c:2931 [inline]
> >> > > > kmem_cache_alloc_trace+0xc53/0x1030 mm/slub.c:2948
> >> > > > kmalloc include/linux/slab.h:554 [inline]
> >> > > > kzalloc include/linux/slab.h:684 [inline]
> >> > > > ____ip_mc_inc_group+0x4d7/0x10b0 net/ipv4/igmp.c:1435
> >> > >
> >> > > This allocates ip_mc_list, but it uses kzalloc. Can that ever count as
> >> > > uninitialized?
> >> >
> >> > Yes, kzalloc should never be a source of uninitialized-ness.
> >> > But it's not actually this kzalloc, it's underlying page allocation
> >> > (that is allocated uninitialized, so can be source of
> >> > uninitialized-ness).
> >> > If it would be this kzalloc, then stack would be shorter, along the
> >> > lines of kzalloc->kmem_cache_alloc_trace->kmsan_save_stack_with_flags.
> >> >
> >> > This smells like a wild access in virtio_net_hdr_to_skb, which just
> >> > hit a random uninit somewhere.
> >> > Searching for virtio_net_hdr_to_skb I found this:
> >> >
> >> > KASAN: use-after-free Read in eth_header_parse_protocol
> >> > https://syzkaller.appspot.com/bug?id=a486048b63065fd224f57b16d5a2fdece2b40eca
> >> >
> >> > Can it be a dup of that bug?
> >>
> >> Great find.
> >>
> >> That commit is not yet present at kmsan.git at 4ebaab5fb428.
> >>
> >> Certainly sounds plausible.
> >
> > Then let's consider:
> >
> > #syz dup: KASAN: use-after-free Read in eth_header_parse_protocol
>
> Can't dup bug to a bug in different reporting (upstream->internal).Please dup syzbot bugs only onto syzbot bugs for the same kernel/reporting.
Let's try:
#syz fix: net: ensure mac header is set in virtio_net_hdr_to_skb()
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