KASAN: global-out-of-bounds Read in smc_nl_get_sys_info

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    3db1a3fa Merge tag 'staging-5.11-rc1' of git://git.kernel...
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=121dc937500000
kernel config:  https://syzkaller.appspot.com/x/.config?x=2764fc28a92339f9
dashboard link: https://syzkaller.appspot.com/bug?extid=f4708c391121cfc58396
compiler:       gcc (GCC) 10.1.0-syz 20200507
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=16522287500000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1144680f500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f4708c391121cfc58396@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: global-out-of-bounds in string_nocheck lib/vsprintf.c:611 [inline]
BUG: KASAN: global-out-of-bounds in string+0x39c/0x3d0 lib/vsprintf.c:693
Read of size 1 at addr ffffffff8faea960 by task syz-executor646/8509

CPU: 0 PID: 8509 Comm: syz-executor646 Not tainted 5.10.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:79 [inline]
 dump_stack+0x107/0x163 lib/dump_stack.c:120
 print_address_description.constprop.0.cold+0x5/0x4c8 mm/kasan/report.c:385
 __kasan_report mm/kasan/report.c:545 [inline]
 kasan_report.cold+0x1f/0x37 mm/kasan/report.c:562
 string_nocheck lib/vsprintf.c:611 [inline]
 string+0x39c/0x3d0 lib/vsprintf.c:693
 vsnprintf+0x71b/0x14f0 lib/vsprintf.c:2618
 snprintf+0xbb/0xf0 lib/vsprintf.c:2751
 smc_nl_get_sys_info+0x493/0x880 net/smc/smc_core.c:249
 genl_lock_dumpit+0x60/0x90 net/netlink/genetlink.c:623
 netlink_dump+0x4b9/0xb70 net/netlink/af_netlink.c:2268
 __netlink_dump_start+0x642/0x900 net/netlink/af_netlink.c:2373
 genl_family_rcv_msg_dumpit+0x2af/0x310 net/netlink/genetlink.c:686
 genl_family_rcv_msg net/netlink/genetlink.c:780 [inline]
 genl_rcv_msg+0x434/0x580 net/netlink/genetlink.c:800
 netlink_rcv_skb+0x153/0x420 net/netlink/af_netlink.c:2494
 genl_rcv+0x24/0x40 net/netlink/genetlink.c:811
 netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
 netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1330
 netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec net/socket.c:652 [inline]
 sock_sendmsg+0xcf/0x120 net/socket.c:672
 ____sys_sendmsg+0x6e8/0x810 net/socket.c:2336
 ___sys_sendmsg+0xf3/0x170 net/socket.c:2390
 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2423
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x440299
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 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 7b 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fff4b943e58 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440299
RDX: 0000000000000000 RSI: 0000000020000180 RDI: 0000000000000003
RBP: 00000000006ca018 R08: 0000000000000000 R09: 00000000004002c8
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401aa0
R13: 0000000000401b30 R14: 0000000000000000 R15: 0000000000000000

The buggy address belongs to the variable:
 smc_hostname+0x20/0x40

Memory state around the buggy address:
 ffffffff8faea800: 00 00 f9 f9 f9 f9 f9 f9 00 00 f9 f9 f9 f9 f9 f9
 ffffffff8faea880: 00 00 f9 f9 f9 f9 f9 f9 00 00 f9 f9 f9 f9 f9 f9
>ffffffff8faea900: 00 f9 f9 f9 f9 f9 f9 f9 00 00 00 00 f9 f9 f9 f9
                                                       ^
 ffffffff8faea980: 04 f9 f9 f9 f9 f9 f9 f9 00 00 f9 f9 f9 f9 f9 f9
 ffffffff8faeaa00: 00 00 f9 f9 f9 f9 f9 f9 00 00 f9 f9 f9 f9 f9 f9
==================================================================


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