Re: KMSAN: uninit-value in __skb_flow_dissect (3)

[Alexander Potapenko]

On Wed, Jul 22, 2020 at 11:53 AM syzbot
<syzbot+051a531e8f1f59cf6dc9@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:

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


> 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=154bb20f100000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c534a9fad6323722
> dashboard link: https://syzkaller.appspot.com/bug?extid=051a531e8f1f59cf6dc9
> compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
> userspace arch: i386
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13946658900000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=17adcb6f100000
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+051a531e8f1f59cf6dc9@xxxxxxxxxxxxxxxxxxxxxxxxx
>
> batman_adv: batadv0: Interface activated: batadv_slave_1
> =====================================================
> BUG: KMSAN: uninit-value in __skb_flow_dissect+0x30f0/0x8440 net/core/flow_dissector.c:1163
> CPU: 0 PID: 8524 Comm: syz-executor152 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_flow_dissect+0x30f0/0x8440 net/core/flow_dissector.c:1163
>  skb_flow_dissect_flow_keys include/linux/skbuff.h:1310 [inline]
>  ___skb_get_hash net/core/flow_dissector.c:1520 [inline]
>  __skb_get_hash+0x131/0x480 net/core/flow_dissector.c:1586
>  skb_get_hash include/linux/skbuff.h:1348 [inline]
>  udp_flow_src_port+0xa5/0x690 include/net/udp.h:220
>  geneve_xmit_skb drivers/net/geneve.c:895 [inline]
>  geneve_xmit+0xdf1/0x2bf0 drivers/net/geneve.c:1005
>  __netdev_start_xmit include/linux/netdevice.h:4611 [inline]
>  netdev_start_xmit include/linux/netdevice.h:4625 [inline]
>  xmit_one net/core/dev.c:3556 [inline]
>  dev_hard_start_xmit+0x50e/0xa70 net/core/dev.c:3572
>  __dev_queue_xmit+0x2f8d/0x3b20 net/core/dev.c:4131
>  dev_queue_xmit+0x4b/0x60 net/core/dev.c:4164
>  pppoe_sendmsg+0xb43/0xb90 drivers/net/ppp/pppoe.c:900
>  sock_sendmsg_nosec net/socket.c:652 [inline]
>  sock_sendmsg net/socket.c:672 [inline]
>  kernel_sendmsg+0x433/0x440 net/socket.c:692
>  sock_no_sendpage+0x235/0x300 net/core/sock.c:2853
>  kernel_sendpage net/socket.c:3644 [inline]
>  sock_sendpage+0x25b/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_compat_sys_sendfile fs/read_write.c:1622 [inline]
>  __se_compat_sys_sendfile+0x301/0x3c0 fs/read_write.c:1605
>  __ia32_compat_sys_sendfile+0x56/0x70 fs/read_write.c:1605
>  do_syscall_32_irqs_on arch/x86/entry/common.c:430 [inline]
>  __do_fast_syscall_32+0x2aa/0x400 arch/x86/entry/common.c:477
>  do_fast_syscall_32+0x6b/0xd0 arch/x86/entry/common.c:505
>  do_SYSENTER_32+0x73/0x90 arch/x86/entry/common.c:554
>  entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
> RIP: 0023:0xf7f13549
> Code: Bad RIP value.
> RSP: 002b:00000000ffd520cc EFLAGS: 00000217 ORIG_RAX: 00000000000000bb
> RAX: ffffffffffffffda RBX: 0000000000000006 RCX: 0000000000000005
> RDX: 0000000000000000 RSI: 000000007fffffff RDI: 0000000000000006
> RBP: 0000000020000000 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: 0000000000000000 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
>  pppoe_sendmsg+0xaed/0xb90 drivers/net/ppp/pppoe.c:896
>  sock_sendmsg_nosec net/socket.c:652 [inline]
>  sock_sendmsg net/socket.c:672 [inline]
>  kernel_sendmsg+0x433/0x440 net/socket.c:692
>  sock_no_sendpage+0x235/0x300 net/core/sock.c:2853
>  kernel_sendpage net/socket.c:3644 [inline]
>  sock_sendpage+0x25b/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_compat_sys_sendfile fs/read_write.c:1622 [inline]
>  __se_compat_sys_sendfile+0x301/0x3c0 fs/read_write.c:1605
>  __ia32_compat_sys_sendfile+0x56/0x70 fs/read_write.c:1605
>  do_syscall_32_irqs_on arch/x86/entry/common.c:430 [inline]
>  __do_fast_syscall_32+0x2aa/0x400 arch/x86/entry/common.c:477
>  do_fast_syscall_32+0x6b/0xd0 arch/x86/entry/common.c:505
>  do_SYSENTER_32+0x73/0x90 arch/x86/entry/common.c:554
>  entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
>
> Local variable ----hdr@pppoe_sendmsg created at:
>  pppoe_sendmsg+0xa6/0xb90 drivers/net/ppp/pppoe.c:843
>  pppoe_sendmsg+0xa6/0xb90 drivers/net/ppp/pppoe.c:843
> =====================================================
>
>
> ---
> This report is generated by a bot. It may contain errors.
> See https://goo.gl/tpsmEJ for more information about syzbot.
> syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxxx
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> syzbot can test patches for this issue, for details see:
> https://goo.gl/tpsmEJ#testing-patches



-- 
Alexander Potapenko
Software Engineer

Google Germany GmbH
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