KASAN: slab-out-of-bounds Read in netlink_broadcast_filtered

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d18b78ab Linux 4.19.141
git tree: linux-4.19.y
console output: https://syzkaller.appspot.com/x/log.txt?x=153c19a9900000
kernel config: https://syzkaller.appspot.com/x/.config?x=434d9db52d13a8e1
dashboard link: https://syzkaller.appspot.com/bug?extid=20f6fd029991d8ad3353
compiler: gcc (GCC) 10.1.0-syz 20200507

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+20f6fd...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in netlink_broadcast_filtered+0xa87/0xbc0 net/netlink/af_netlink.c:1517
Read of size 8 at addr ffff88821b7dbf60 by task kworker/u4:0/1189

CPU: 1 PID: 1189 Comm: kworker/u4:0 Not tainted 4.19.141-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: netns cleanup_net
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1fc/0x2fe lib/dump_stack.c:118
print_address_description.cold+0x54/0x219 mm/kasan/report.c:256
kasan_report_error.cold+0x8a/0x1c7 mm/kasan/report.c:354
kasan_report mm/kasan/report.c:412 [inline]
__asan_report_load8_noabort+0x88/0x90 mm/kasan/report.c:433
netlink_broadcast_filtered+0xa87/0xbc0 net/netlink/af_netlink.c:1517
netlink_broadcast net/netlink/af_netlink.c:1542 [inline]
nlmsg_multicast include/net/netlink.h:591 [inline]
nlmsg_notify+0x157/0x1a0 net/netlink/af_netlink.c:2498
inet_netconf_notify_devconf+0x13a/0x250 net/ipv4/devinet.c:1927
__devinet_sysctl_unregister net/ipv4/devinet.c:2371 [inline]
devinet_exit_net+0x10f/0x280 net/ipv4/devinet.c:2494
ops_exit_list+0xa5/0x150 net/core/net_namespace.c:153
cleanup_net+0x3b4/0x8b0 net/core/net_namespace.c:553
process_one_work+0x864/0x1570 kernel/workqueue.c:2155
worker_thread+0x64c/0x1130 kernel/workqueue.c:2298
kthread+0x30b/0x410 kernel/kthread.c:246
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:415

Allocated by task 1:
kmem_cache_alloc+0x122/0x370 mm/slab.c:3559
getname_flags+0xce/0x590 fs/namei.c:140
user_path_at_empty+0x2a/0x50 fs/namei.c:2609
user_path_at include/linux/namei.h:57 [inline]
vfs_statx+0x113/0x210 fs/stat.c:185
vfs_lstat include/linux/fs.h:3134 [inline]
__do_sys_newlstat fs/stat.c:350 [inline]
__se_sys_newlstat+0x96/0x120 fs/stat.c:344
do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 1:
__cache_free mm/slab.c:3503 [inline]
kmem_cache_free+0x7f/0x260 mm/slab.c:3765
putname+0xe1/0x120 fs/namei.c:261
filename_lookup+0x3d0/0x5a0 fs/namei.c:2358
user_path_at include/linux/namei.h:57 [inline]
vfs_statx+0x113/0x210 fs/stat.c:185
vfs_lstat include/linux/fs.h:3134 [inline]
__do_sys_newlstat fs/stat.c:350 [inline]
__se_sys_newlstat+0x96/0x120 fs/stat.c:344
do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88821b7da380
which belongs to the cache names_cache of size 4096
The buggy address is located 3040 bytes to the right of
4096-byte region [ffff88821b7da380, ffff88821b7db380)
The buggy address belongs to the page:
page:ffffea00086df680 count:1 mapcount:0 mapping:ffff8880aa00ab40 index:0x0 compound_mapcount: 0
flags: 0x57ffe0000008100(slab|head)
raw: 057ffe0000008100 ffffea000834af08 ffffea000839b888 ffff8880aa00ab40
raw: 0000000000000000 ffff88821b7da380 0000000100000001 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88821b7dbe00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88821b7dbe80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88821b7dbf00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88821b7dbf80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88821b7dc000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.