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Date:   Wed, 22 Jul 2020 18:41:52 +0200
From:   Alexander Potapenko <glider@...gle.com>
To:     syzbot <syzbot+721b564cd88ebb710182@...kaller.appspotmail.com>
Cc:     coreteam@...filter.org, David Miller <davem@...emloft.net>,
        fw@...len.de, kadlec@...filter.org, kuba@...nel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        netfilter-devel@...r.kernel.org, pablo@...filter.org,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: KMSAN: uninit-value in __skb_checksum_complete (4)

On Mon, Jul 20, 2020 at 2:25 AM syzbot
<syzbot+721b564cd88ebb710182@...kaller.appspotmail.com> wrote:
>
> syzbot has found a reproducer for the following issue on:
>
> HEAD commit:    14525656 compiler.h: reinstate missing KMSAN_INIT
> git tree:       https://github.com/google/kmsan.git master
> console output: https://syzkaller.appspot.com/x/log.txt?x=16a7c827100000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c534a9fad6323722
> dashboard link: https://syzkaller.appspot.com/bug?extid=721b564cd88ebb710182
> compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=115be9d7100000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15b9425f100000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+721b564cd88ebb710182@...kaller.appspotmail.com

Sorry for the noise. This is a false report caused by incorrect
copy_to_user() instrumentation after KMSAN rebase.
Should be fixed now.

#syz invalid

> =====================================================
> BUG: KMSAN: uninit-value in __skb_checksum_complete+0x37f/0x540 net/core/skbuff.c:2850
> CPU: 1 PID: 8457 Comm: syz-executor769 Not tainted 5.8.0-rc5-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x1df/0x240 lib/dump_stack.c:118
>  kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:121
>  __msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215
>  __skb_checksum_complete+0x37f/0x540 net/core/skbuff.c:2850
>  nf_ip_checksum+0x53b/0x740 net/netfilter/utils.c:36
>  nf_nat_icmp_reply_translation+0x2ba/0x980 net/netfilter/nf_nat_proto.c:578
>  nf_nat_ipv4_fn net/netfilter/nf_nat_proto.c:637 [inline]
>  nf_nat_ipv4_local_fn+0x215/0x830 net/netfilter/nf_nat_proto.c:708
>  nf_hook_entry_hookfn include/linux/netfilter.h:135 [inline]
>  nf_hook_slow+0x16e/0x400 net/netfilter/core.c:512
>  nf_hook include/linux/netfilter.h:262 [inline]
>  __ip_local_out+0x69b/0x800 net/ipv4/ip_output.c:114
>  ip_local_out net/ipv4/ip_output.c:123 [inline]
>  ip_send_skb net/ipv4/ip_output.c:1560 [inline]
>  ip_push_pending_frames+0x16f/0x460 net/ipv4/ip_output.c:1580
>  icmp_push_reply+0x660/0x710 net/ipv4/icmp.c:390
>  __icmp_send+0x23ca/0x3150 net/ipv4/icmp.c:740
>  icmp_send include/net/icmp.h:43 [inline]
>  ip_fragment+0x39f/0x400 net/ipv4/ip_output.c:579
>  __ip_finish_output+0xd34/0xd80 net/ipv4/ip_output.c:304
>  ip_finish_output+0x166/0x410 net/ipv4/ip_output.c:316
>  NF_HOOK_COND include/linux/netfilter.h:296 [inline]
>  ip_output+0x593/0x680 net/ipv4/ip_output.c:430
>  dst_output include/net/dst.h:443 [inline]
>  ip_local_out net/ipv4/ip_output.c:125 [inline]
>  __ip_queue_xmit+0x1b5c/0x21a0 net/ipv4/ip_output.c:530
>  ip_queue_xmit include/net/ip.h:237 [inline]
>  l2tp_ip_sendmsg+0x1477/0x1870 net/l2tp/l2tp_ip.c:508
>  inet_sendmsg+0x2d8/0x2e0 net/ipv4/af_inet.c:814
>  sock_sendmsg_nosec net/socket.c:652 [inline]
>  sock_sendmsg net/socket.c:672 [inline]
>  kernel_sendmsg+0x384/0x440 net/socket.c:692
>  sock_no_sendpage+0x235/0x300 net/core/sock.c:2853
>  kernel_sendpage net/socket.c:3642 [inline]
>  sock_sendpage+0x1e1/0x2c0 net/socket.c:945
>  pipe_to_sendpage+0x38c/0x4c0 fs/splice.c:448
>  splice_from_pipe_feed fs/splice.c:502 [inline]
>  __splice_from_pipe+0x565/0xf00 fs/splice.c:626
>  splice_from_pipe fs/splice.c:661 [inline]
>  generic_splice_sendpage+0x1d5/0x2d0 fs/splice.c:834
>  do_splice_from fs/splice.c:846 [inline]
>  direct_splice_actor+0x1fd/0x580 fs/splice.c:1016
>  splice_direct_to_actor+0x6b2/0xf50 fs/splice.c:971
>  do_splice_direct+0x342/0x580 fs/splice.c:1059
>  do_sendfile+0x101b/0x1d40 fs/read_write.c:1540
>  __do_sys_sendfile64 fs/read_write.c:1601 [inline]
>  __se_sys_sendfile64+0x2bb/0x360 fs/read_write.c:1587
>  __x64_sys_sendfile64+0x56/0x70 fs/read_write.c:1587
>  do_syscall_64+0xb0/0x150 arch/x86/entry/common.c:386
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x440409
> Code: Bad RIP value.
> RSP: 002b:00007ffe9c5d76d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
> RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440409
> RDX: 0000000000000000 RSI: 0000000000000005 RDI: 0000000000000003
> RBP: 00000000006cb018 R08: 0000000000000014 R09: 65732f636f72702f
> R10: 0800000080004103 R11: 0000000000000246 R12: 0000000000401c70
> R13: 0000000000401d00 R14: 0000000000000000 R15: 0000000000000000
>
> Uninit was stored to memory at:
>  kmsan_save_stack_with_flags mm/kmsan/kmsan.c:144 [inline]
>  kmsan_internal_chain_origin+0xad/0x130 mm/kmsan/kmsan.c:310
>  kmsan_memcpy_memmove_metadata+0x272/0x2e0 mm/kmsan/kmsan.c:247
>  kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:267
>  __msan_memcpy+0x43/0x50 mm/kmsan/kmsan_instr.c:116
>  csum_partial_copy+0xae/0x100 lib/checksum.c:154
>  skb_copy_and_csum_bits+0x227/0x1130 net/core/skbuff.c:2737
>  icmp_glue_bits+0x166/0x380 net/ipv4/icmp.c:353
>  __ip_append_data+0x47c4/0x5630 net/ipv4/ip_output.c:1131
>  ip_append_data+0x328/0x480 net/ipv4/ip_output.c:1315
>  icmp_push_reply+0x206/0x710 net/ipv4/icmp.c:371
>  __icmp_send+0x23ca/0x3150 net/ipv4/icmp.c:740
>  icmp_send include/net/icmp.h:43 [inline]
>  ip_fragment+0x39f/0x400 net/ipv4/ip_output.c:579
>  __ip_finish_output+0xd34/0xd80 net/ipv4/ip_output.c:304
>  ip_finish_output+0x166/0x410 net/ipv4/ip_output.c:316
>  NF_HOOK_COND include/linux/netfilter.h:296 [inline]
>  ip_output+0x593/0x680 net/ipv4/ip_output.c:430
>  dst_output include/net/dst.h:443 [inline]
>  ip_local_out net/ipv4/ip_output.c:125 [inline]
>  __ip_queue_xmit+0x1b5c/0x21a0 net/ipv4/ip_output.c:530
>  ip_queue_xmit include/net/ip.h:237 [inline]
>  l2tp_ip_sendmsg+0x1477/0x1870 net/l2tp/l2tp_ip.c:508
>  inet_sendmsg+0x2d8/0x2e0 net/ipv4/af_inet.c:814
>  sock_sendmsg_nosec net/socket.c:652 [inline]
>  sock_sendmsg net/socket.c:672 [inline]
>  kernel_sendmsg+0x384/0x440 net/socket.c:692
>  sock_no_sendpage+0x235/0x300 net/core/sock.c:2853
>  kernel_sendpage net/socket.c:3642 [inline]
>  sock_sendpage+0x1e1/0x2c0 net/socket.c:945
>  pipe_to_sendpage+0x38c/0x4c0 fs/splice.c:448
>  splice_from_pipe_feed fs/splice.c:502 [inline]
>  __splice_from_pipe+0x565/0xf00 fs/splice.c:626
>  splice_from_pipe fs/splice.c:661 [inline]
>  generic_splice_sendpage+0x1d5/0x2d0 fs/splice.c:834
>  do_splice_from fs/splice.c:846 [inline]
>  direct_splice_actor+0x1fd/0x580 fs/splice.c:1016
>  splice_direct_to_actor+0x6b2/0xf50 fs/splice.c:971
>  do_splice_direct+0x342/0x580 fs/splice.c:1059
>  do_sendfile+0x101b/0x1d40 fs/read_write.c:1540
>  __do_sys_sendfile64 fs/read_write.c:1601 [inline]
>  __se_sys_sendfile64+0x2bb/0x360 fs/read_write.c:1587
>  __x64_sys_sendfile64+0x56/0x70 fs/read_write.c:1587
>  do_syscall_64+0xb0/0x150 arch/x86/entry/common.c:386
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Uninit was stored to memory at:
>  kmsan_save_stack_with_flags mm/kmsan/kmsan.c:144 [inline]
>  kmsan_internal_chain_origin+0xad/0x130 mm/kmsan/kmsan.c:310
>  kmsan_memcpy_memmove_metadata+0x272/0x2e0 mm/kmsan/kmsan.c:247
>  kmsan_memcpy_metadata+0xb/0x10 mm/kmsan/kmsan.c:267
>  __msan_memcpy+0x43/0x50 mm/kmsan/kmsan_instr.c:116
>  _copy_from_iter_full+0xbfe/0x13b0 lib/iov_iter.c:793
>  copy_from_iter_full include/linux/uio.h:156 [inline]
>  memcpy_from_msg include/linux/skbuff.h:3566 [inline]
>  l2tp_ip_sendmsg+0x6a5/0x1870 net/l2tp/l2tp_ip.c:462
>  inet_sendmsg+0x2d8/0x2e0 net/ipv4/af_inet.c:814
>  sock_sendmsg_nosec net/socket.c:652 [inline]
>  sock_sendmsg net/socket.c:672 [inline]
>  kernel_sendmsg+0x384/0x440 net/socket.c:692
>  sock_no_sendpage+0x235/0x300 net/core/sock.c:2853
>  kernel_sendpage net/socket.c:3642 [inline]
>  sock_sendpage+0x1e1/0x2c0 net/socket.c:945
>  pipe_to_sendpage+0x38c/0x4c0 fs/splice.c:448
>  splice_from_pipe_feed fs/splice.c:502 [inline]
>  __splice_from_pipe+0x565/0xf00 fs/splice.c:626
>  splice_from_pipe fs/splice.c:661 [inline]
>  generic_splice_sendpage+0x1d5/0x2d0 fs/splice.c:834
>  do_splice_from fs/splice.c:846 [inline]
>  direct_splice_actor+0x1fd/0x580 fs/splice.c:1016
>  splice_direct_to_actor+0x6b2/0xf50 fs/splice.c:971
>  do_splice_direct+0x342/0x580 fs/splice.c:1059
>  do_sendfile+0x101b/0x1d40 fs/read_write.c:1540
>  __do_sys_sendfile64 fs/read_write.c:1601 [inline]
>  __se_sys_sendfile64+0x2bb/0x360 fs/read_write.c:1587
>  __x64_sys_sendfile64+0x56/0x70 fs/read_write.c:1587
>  do_syscall_64+0xb0/0x150 arch/x86/entry/common.c:386
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Uninit was created at:
>  kmsan_save_stack_with_flags+0x3c/0x90 mm/kmsan/kmsan.c:144
>  kmsan_internal_alloc_meta_for_pages mm/kmsan/kmsan_shadow.c:269 [inline]
>  kmsan_alloc_page+0xb9/0x180 mm/kmsan/kmsan_shadow.c:293
>  __alloc_pages_nodemask+0x56a2/0x5dc0 mm/page_alloc.c:4889
>  alloc_pages_current+0x672/0x990 mm/mempolicy.c:2292
>  alloc_pages include/linux/gfp.h:545 [inline]
>  push_pipe+0x605/0xb70 lib/iov_iter.c:537
>  __pipe_get_pages lib/iov_iter.c:1278 [inline]
>  pipe_get_pages_alloc lib/iov_iter.c:1385 [inline]
>  iov_iter_get_pages_alloc+0x18a9/0x21c0 lib/iov_iter.c:1403
>  default_file_splice_read fs/splice.c:385 [inline]
>  do_splice_to+0x4fc/0x14f0 fs/splice.c:871
>  splice_direct_to_actor+0x45c/0xf50 fs/splice.c:950
>  do_splice_direct+0x342/0x580 fs/splice.c:1059
>  do_sendfile+0x101b/0x1d40 fs/read_write.c:1540
>  __do_sys_sendfile64 fs/read_write.c:1601 [inline]
>  __se_sys_sendfile64+0x2bb/0x360 fs/read_write.c:1587
>  __x64_sys_sendfile64+0x56/0x70 fs/read_write.c:1587
>  do_syscall_64+0xb0/0x150 arch/x86/entry/common.c:386
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> =====================================================
>


-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
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