Re: KMSAN: uninit-value in ebt_stp_mt_check (2)

[syzbot]

syzbot has found a reproducer for the following crash on:

HEAD commit:    c6a6aed994b6 kmsan: remove dead code to trigger syzbot build
git tree:       https://github.com/google/kmsan.git/master
console output: https://syzkaller.appspot.com/x/log.txt?x=122606bf800000
kernel config:  https://syzkaller.appspot.com/x/.config?x=848e40757852af3e
dashboard link: https://syzkaller.appspot.com/bug?extid=da4494182233c23a5fcf
compiler:       clang version 7.0.0 (trunk 334104)
syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=121f481f800000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=121fbbd7800000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+da4494182233c23a5fcf@xxxxxxxxxxxxxxxxxxxxxxxxx

random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
random: sshd: uninitialized urandom read (32 bytes read)
==================================================================
BUG: KMSAN: uninit-value in ebt_stp_mt_check+0x24b/0x450  
net/bridge/netfilter/ebt_stp.c:162
CPU: 1 PID: 4523 Comm: syz-executor710 Not tainted 4.17.0+ #3
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+0x185/0x1d0 lib/dump_stack.c:113
 kmsan_report+0x149/0x260 mm/kmsan/kmsan.c:1084
 __msan_warning_32+0x6e/0xc0 mm/kmsan/kmsan_instr.c:620
 ebt_stp_mt_check+0x24b/0x450 net/bridge/netfilter/ebt_stp.c:162
 xt_check_match+0x1438/0x1650 net/netfilter/x_tables.c:506
 ebt_check_match net/bridge/netfilter/ebtables.c:372 [inline]
 ebt_check_entry net/bridge/netfilter/ebtables.c:702 [inline]
 translate_table+0x4e88/0x6120 net/bridge/netfilter/ebtables.c:943
 do_replace_finish+0x1258/0x2ea0 net/bridge/netfilter/ebtables.c:999
 do_replace+0x719/0x780 net/bridge/netfilter/ebtables.c:1138
 do_ebt_set_ctl+0x2ab/0x3c0 net/bridge/netfilter/ebtables.c:1517
 nf_sockopt net/netfilter/nf_sockopt.c:106 [inline]
 nf_setsockopt+0x47c/0x4e0 net/netfilter/nf_sockopt.c:115
 ip_setsockopt+0x24b/0x2b0 net/ipv4/ip_sockglue.c:1251
 udp_setsockopt+0x108/0x1b0 net/ipv4/udp.c:2416
 sock_common_setsockopt+0x13b/0x170 net/core/sock.c:3039
 __sys_setsockopt+0x496/0x540 net/socket.c:1903
 __do_sys_setsockopt net/socket.c:1914 [inline]
 __se_sys_setsockopt net/socket.c:1911 [inline]
 __x64_sys_setsockopt+0x15c/0x1c0 net/socket.c:1911
 do_syscall_64+0x15b/0x230 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x43fd89
RSP: 002b:00007ffc9d7edb28 EFLAGS: 00000213 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 000000000043fd89
RDX: 0000000000000080 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000300 R09: 00000000004002c8
R10: 0000000020000480 R11: 0000000000000213 R12: 00000000004016b0
R13: 0000000000401740 R14: 0000000000000000 R15: 0000000000000000

Local variable description: ----mtpar.i@translate_table
Variable was created at:
 translate_table+0xbb/0x6120 net/bridge/netfilter/ebtables.c:831
 do_replace_finish+0x1258/0x2ea0 net/bridge/netfilter/ebtables.c:999
==================================================================