KASAN: stack-out-of-bounds Write in ax25_getname

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    8fe28cb58bcb Linux 4.20
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1604d02d400000
kernel config:  https://syzkaller.appspot.com/x/.config?x=7d581260bae0899a
dashboard link: https://syzkaller.appspot.com/bug?extid=6a29097222b4d3b8617c
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=114a9ec3400000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+6a29097222b4d3b8617c@xxxxxxxxxxxxxxxxxxxxxxxxx

IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready
IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready
8021q: adding VLAN 0 to HW filter on device team0
==================================================================
BUG: KASAN: stack-out-of-bounds in memset include/linux/string.h:337  
[inline]
BUG: KASAN: stack-out-of-bounds in ax25_getname+0x58/0x790  
net/ax25/af_ax25.c:1399
Write of size 72 at addr ffff8881d8547b80 by task syz-executor0/8181

CPU: 0 PID: 8181 Comm: syz-executor0 Not tainted 4.20.0 #166
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+0x1d3/0x2c6 lib/dump_stack.c:113
 print_address_description.cold.8+0x9/0x1ff mm/kasan/report.c:256
 kasan_report_error mm/kasan/report.c:354 [inline]
 kasan_report.cold.9+0x242/0x309 mm/kasan/report.c:412
 check_memory_region_inline mm/kasan/kasan.c:260 [inline]
 check_memory_region+0x13e/0x1b0 mm/kasan/kasan.c:267
 memset+0x23/0x40 mm/kasan/kasan.c:285
 memset include/linux/string.h:337 [inline]
 ax25_getname+0x58/0x790 net/ax25/af_ax25.c:1399
 get_raw_socket drivers/vhost/net.c:1397 [inline]
 get_socket drivers/vhost/net.c:1453 [inline]
 vhost_net_set_backend drivers/vhost/net.c:1488 [inline]
 vhost_net_ioctl+0x139c/0x1bf0 drivers/vhost/net.c:1679
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:509 [inline]
 do_vfs_ioctl+0x1de/0x1790 fs/ioctl.c:696
 ksys_ioctl+0xa9/0xd0 fs/ioctl.c:713
 __do_sys_ioctl fs/ioctl.c:720 [inline]
 __se_sys_ioctl fs/ioctl.c:718 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:718
 do_syscall_64+0x1b9/0x820 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x457759
Code: fd b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 cb b3 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f25cd3fbc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000457759
RDX: 0000000020f1dff8 RSI: 000000004008af30 RDI: 0000000000000004
RBP: 000000000073bf00 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f25cd3fc6d4
R13: 00000000004c1dd4 R14: 00000000004d40e0 R15: 00000000ffffffff

The buggy address belongs to the page:
page:ffffea00076151c0 count:0 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0x2fffc0000000000()
raw: 02fffc0000000000 0000000000000000 ffffffff07610101 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff8881d8547a80: 00 f2 f2 f2 f2 f2 f2 f2 00 f2 f2 f2 f2 f2 f2 f2
 ffff8881d8547b00: 00 f2 f2 f2 f2 f2 f2 f2 04 f2 f2 f2 f2 f2 f2 f2
> ffff8881d8547b80: 00 00 00 00 00 00 04 f2 00 00 00 00 00 00 00 00
                                     ^
 ffff8881d8547c00: 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 f2
 ffff8881d8547c80: f2 f2 f2 f2 f2 f2 00 00 00 f2 f2 f2 f2 f2 00 00
==================================================================


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