On Mon, May 17, 2021 at 4:06 PM Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx> wrote: > > On Mon, May 17, 2021 at 7:27 AM syzbot > <syzbot+106457891e3cf3b273a9@xxxxxxxxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx > > > > ===================================================== > > 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?
