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SubjectKASAN: use-after-free Read in dev_get_by_name
From
Hello,

syzbot found the following crash on:

HEAD commit: 4e99b321 Merge tag 'nfs-for-5.8-2' of git://git.linux-nfs...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1013cb29100000
kernel config: https://syzkaller.appspot.com/x/.config?x=20c907630cbdbe5
dashboard link: https://syzkaller.appspot.com/bug?extid=86e957379663a156cd31
compiler: clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1689e8f5100000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=144f07bb100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+86e957379663a156cd31@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in strnlen+0x63/0x80 lib/string.c:561
Read of size 1 at addr ffff88809f3e9c18 by task syz-executor276/7264

CPU: 0 PID: 7264 Comm: syz-executor276 Not tainted 5.8.0-rc2-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+0x1f0/0x31e lib/dump_stack.c:118
print_address_description+0x66/0x5a0 mm/kasan/report.c:383
__kasan_report mm/kasan/report.c:513 [inline]
kasan_report+0x132/0x1d0 mm/kasan/report.c:530
strnlen+0x63/0x80 lib/string.c:561
dev_name_hash net/core/dev.c:208 [inline]
netdev_name_node_lookup_rcu net/core/dev.c:290 [inline]
dev_get_by_name_rcu net/core/dev.c:883 [inline]
dev_get_by_name+0x9b/0x2a0 net/core/dev.c:905
lookup_interface drivers/net/wireguard/netlink.c:63 [inline]
wg_get_device_start+0x1fb/0x2d0 drivers/net/wireguard/netlink.c:203
genl_start+0x390/0x570 net/netlink/genetlink.c:556
__netlink_dump_start+0x3d2/0x700 net/netlink/af_netlink.c:2343
genl_family_rcv_msg_dumpit net/netlink/genetlink.c:638 [inline]
genl_family_rcv_msg net/netlink/genetlink.c:733 [inline]
genl_rcv_msg+0xb03/0xe00 net/netlink/genetlink.c:753
netlink_rcv_skb+0x190/0x3a0 net/netlink/af_netlink.c:2469
genl_rcv+0x24/0x40 net/netlink/genetlink.c:764
netlink_unicast_kernel net/netlink/af_netlink.c:1303 [inline]
netlink_unicast+0x786/0x940 net/netlink/af_netlink.c:1329
netlink_sendmsg+0xa57/0xd70 net/netlink/af_netlink.c:1918
sock_sendmsg_nosec net/socket.c:652 [inline]
sock_sendmsg net/socket.c:672 [inline]
____sys_sendmsg+0x519/0x800 net/socket.c:2352
___sys_sendmsg net/socket.c:2406 [inline]
__sys_sendmsg+0x2b1/0x360 net/socket.c:2439
do_syscall_64+0x73/0xe0 arch/x86/entry/common.c:359
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x44a809
Code: Bad RIP value.
RSP: 002b:00007fed6f920da8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000006dbc28 RCX: 000000000044a809
RDX: 0000000000000000 RSI: 0000000020000200 RDI: 0000000000000004
RBP: 00000000006dbc20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dbc2c
R13: 0000000000000000 R14: 0000000000316777 R15: 0000000000000000

Allocated by task 7265:
save_stack mm/kasan/common.c:48 [inline]
set_track mm/kasan/common.c:56 [inline]
__kasan_kmalloc+0x103/0x140 mm/kasan/common.c:494
__kmalloc_reserve net/core/skbuff.c:142 [inline]
__alloc_skb+0xde/0x4f0 net/core/skbuff.c:210
alloc_skb include/linux/skbuff.h:1083 [inline]
netlink_alloc_large_skb net/netlink/af_netlink.c:1175 [inline]
netlink_sendmsg+0x7b2/0xd70 net/netlink/af_netlink.c:1893
sock_sendmsg_nosec net/socket.c:652 [inline]
sock_sendmsg net/socket.c:672 [inline]
____sys_sendmsg+0x519/0x800 net/socket.c:2352
___sys_sendmsg net/socket.c:2406 [inline]
__sys_sendmsg+0x2b1/0x360 net/socket.c:2439
do_syscall_64+0x73/0xe0 arch/x86/entry/common.c:359
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Freed by task 7265:
save_stack mm/kasan/common.c:48 [inline]
set_track mm/kasan/common.c:56 [inline]
kasan_set_free_info mm/kasan/common.c:316 [inline]
__kasan_slab_free+0x114/0x170 mm/kasan/common.c:455
__cache_free mm/slab.c:3426 [inline]
kfree+0x10a/0x220 mm/slab.c:3757
skb_release_all net/core/skbuff.c:664 [inline]
__kfree_skb+0x56/0x1c0 net/core/skbuff.c:678
netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
netlink_unicast+0x78e/0x940 net/netlink/af_netlink.c:1329
netlink_sendmsg+0xa57/0xd70 net/netlink/af_netlink.c:1918
sock_sendmsg_nosec net/socket.c:652 [inline]
sock_sendmsg net/socket.c:672 [inline]
____sys_sendmsg+0x519/0x800 net/socket.c:2352
___sys_sendmsg net/socket.c:2406 [inline]
__sys_sendmsg+0x2b1/0x360 net/socket.c:2439
do_syscall_64+0x73/0xe0 arch/x86/entry/common.c:359
entry_SYSCALL_64_after_hwframe+0x44/0xa9

The buggy address belongs to the object at ffff88809f3e9c00
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 24 bytes inside of
512-byte region [ffff88809f3e9c00, ffff88809f3e9e00)
The buggy address belongs to the page:
page:ffffea00027cfa40 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea000294b388 ffffea00029e4388 ffff8880aa400a80
raw: 0000000000000000 ffff88809f3e9000 0000000100000004 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88809f3e9b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88809f3e9b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88809f3e9c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88809f3e9c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88809f3e9d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This bug is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzkaller@googlegroups.com.

syzbot will keep track of this bug report. See:
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syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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