KMSAN: uninit-value in route4_get

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    21c44613 kmsan: page_alloc: more assuring comment
git tree:       https://github.com/google/kmsan.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=111271e4100000
kernel config:  https://syzkaller.appspot.com/x/.config?x=a5915107b3106aaa
dashboard link: https://syzkaller.appspot.com/bug?extid=0f695e9c22e33a40e8b5
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
userspace arch: i386

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+0f695e9c22e33a40e8b5@xxxxxxxxxxxxxxxxxxxxxxxxx

=====================================================
BUG: KMSAN: uninit-value in route4_get+0x2cd/0x3d0 net/sched/cls_route.c:235
CPU: 1 PID: 15044 Comm: syz-executor.4 Not tainted 5.6.0-rc7-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+0x1c9/0x220 lib/dump_stack.c:118
 kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:118
 __msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:215
 route4_get+0x2cd/0x3d0 net/sched/cls_route.c:235
 tc_new_tfilter+0x1f32/0x4f40 net/sched/cls_api.c:2082
 rtnetlink_rcv_msg+0xcb7/0x1570 net/core/rtnetlink.c:5427
 netlink_rcv_skb+0x451/0x650 net/netlink/af_netlink.c:2478
 rtnetlink_rcv+0x50/0x60 net/core/rtnetlink.c:5454
 netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
 netlink_unicast+0xf9e/0x1100 net/netlink/af_netlink.c:1329
 netlink_sendmsg+0x1246/0x14d0 net/netlink/af_netlink.c:1918
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg net/socket.c:672 [inline]
 ____sys_sendmsg+0x12b6/0x1350 net/socket.c:2345
 ___sys_sendmsg net/socket.c:2399 [inline]
 __sys_sendmsg+0x451/0x5f0 net/socket.c:2432
 __compat_sys_sendmsg net/compat.c:642 [inline]
 __do_compat_sys_sendmsg net/compat.c:649 [inline]
 __se_compat_sys_sendmsg net/compat.c:646 [inline]
 __ia32_compat_sys_sendmsg+0xed/0x130 net/compat.c:646
 do_syscall_32_irqs_on arch/x86/entry/common.c:339 [inline]
 do_fast_syscall_32+0x3c7/0x6e0 arch/x86/entry/common.c:410
 entry_SYSENTER_compat+0x68/0x77 arch/x86/entry/entry_64_compat.S:139
RIP: 0023:0xf7f0bd99
Code: 90 e8 0b 00 00 00 f3 90 0f ae e8 eb f9 8d 74 26 00 89 3c 24 c3 90 90 90 90 90 90 90 90 90 90 90 90 51 52 55 89 e5 0f 34 cd 80 <5d> 5a 59 c3 90 90 90 90 eb 0d 90 90 90 90 90 90 90 90 90 90 90 90
RSP: 002b:00000000f5cc40cc EFLAGS: 00000296 ORIG_RAX: 0000000000000172
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000020000280
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000

Uninit was created at:
 kmsan_save_stack_with_flags mm/kmsan/kmsan.c:144 [inline]
 kmsan_internal_poison_shadow+0x66/0xd0 mm/kmsan/kmsan.c:127
 kmsan_slab_alloc+0x8a/0xe0 mm/kmsan/kmsan_hooks.c:80
 slab_alloc_node mm/slub.c:2801 [inline]
 slab_alloc mm/slub.c:2810 [inline]
 kmem_cache_alloc_trace+0x6f3/0xd70 mm/slub.c:2827
 kmalloc include/linux/slab.h:555 [inline]
 batadv_forw_packet_alloc+0x1be/0x6d0 net/batman-adv/send.c:525
 batadv_iv_ogm_aggregate_new net/batman-adv/bat_iv_ogm.c:562 [inline]
 batadv_iv_ogm_queue_add+0x11cb/0x1900 net/batman-adv/bat_iv_ogm.c:670
 batadv_iv_ogm_schedule_buff net/batman-adv/bat_iv_ogm.c:833 [inline]
 batadv_iv_ogm_schedule+0xd4c/0x1430 net/batman-adv/bat_iv_ogm.c:869
 batadv_iv_send_outstanding_bat_ogm_packet+0xbae/0xd50 net/batman-adv/bat_iv_ogm.c:1722
 process_one_work+0x1555/0x1f40 kernel/workqueue.c:2266
 worker_thread+0xef6/0x2450 kernel/workqueue.c:2412
 kthread+0x4b5/0x4f0 kernel/kthread.c:256
 ret_from_fork+0x35/0x40 arch/x86/entry/entry_64.S:353
=====================================================


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