KMSAN: uninit-value in __skb_flow_dissect (3)

[syzbot]

Hello,

syzbot found 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=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+051a53...@syzkaller.appspotmail.com

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 syzk...@googlegroups.com.

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]

On Wed, Jul 22, 2020 at 11:53 AM syzbot
<syzbot+051a53...@syzkaller.appspotmail.com> 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

--
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
Sitz der Gesellschaft: Hamburg