KASAN: use-after-free Read in netdev_name_node_lookup_rcu

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 1590a2e1 Merge tag 'acpi-5.8-rc3' of git://git.kernel.org/..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1664afad100000
kernel config: https://syzkaller.appspot.com/x/.config?x=bf3aec367b9ab569
dashboard link: https://syzkaller.appspot.com/bug?extid=a82be85e09cd5df398fe
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14a1bf1d100000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1514a06b100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+a82be8...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in strnlen+0x64/0x70 lib/string.c:561
Read of size 1 at addr ffff8880933b8c18 by task syz-executor821/6893

CPU: 0 PID: 6893 Comm: syz-executor821 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+0x18f/0x20d lib/dump_stack.c:118
print_address_description.constprop.0.cold+0xae/0x436 mm/kasan/report.c:383
__kasan_report mm/kasan/report.c:513 [inline]
kasan_report.cold+0x1f/0x37 mm/kasan/report.c:530
strnlen+0x64/0x70 lib/string.c:561
strnlen include/linux/string.h:339 [inline]
dev_name_hash net/core/dev.c:208 [inline]
netdev_name_node_lookup_rcu+0x22/0x150 net/core/dev.c:290
dev_get_by_name_rcu net/core/dev.c:883 [inline]
dev_get_by_name+0x7b/0x1e0 net/core/dev.c:905
lookup_interface drivers/net/wireguard/netlink.c:63 [inline]
wg_get_device_start+0x2e4/0x3f0 drivers/net/wireguard/netlink.c:203
genl_start+0x342/0x6e0 net/netlink/genetlink.c:556
__netlink_dump_start+0x585/0x900 net/netlink/af_netlink.c:2343
genl_family_rcv_msg_dumpit+0x2ac/0x310 net/netlink/genetlink.c:638
genl_family_rcv_msg net/netlink/genetlink.c:733 [inline]
genl_rcv_msg+0x797/0x9e0 net/netlink/genetlink.c:753
netlink_rcv_skb+0x15a/0x430 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+0x533/0x7d0 net/netlink/af_netlink.c:1329
netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1918
sock_sendmsg_nosec net/socket.c:652 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:672
____sys_sendmsg+0x6e8/0x810 net/socket.c:2352
___sys_sendmsg+0xf3/0x170 net/socket.c:2406
__sys_sendmsg+0xe5/0x1b0 net/socket.c:2439
do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:359
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x445299
Code: Bad RIP value.
RSP: 002b:00007ffd1e794308 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 0000000000445299
RDX: 0000000000000000 RSI: 0000000020000200 RDI: 0000000000000003
RBP: 0000000000082a5d R08: 0000000000000000 R09: 00000000004002e0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000402430
R13: 00000000004024c0 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 6894:
save_stack+0x1b/0x40 mm/kasan/common.c:48
set_track mm/kasan/common.c:56 [inline]
__kasan_kmalloc.constprop.0+0xc2/0xd0 mm/kasan/common.c:494
__kmalloc_reserve net/core/skbuff.c:142 [inline]
__alloc_skb+0xae/0x550 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+0x94f/0xd90 net/netlink/af_netlink.c:1893
sock_sendmsg_nosec net/socket.c:652 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:672
____sys_sendmsg+0x6e8/0x810 net/socket.c:2352
___sys_sendmsg+0xf3/0x170 net/socket.c:2406
__sys_sendmsg+0xe5/0x1b0 net/socket.c:2439
do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:359
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Freed by task 6894:
save_stack+0x1b/0x40 mm/kasan/common.c:48
set_track mm/kasan/common.c:56 [inline]
kasan_set_free_info mm/kasan/common.c:316 [inline]
__kasan_slab_free+0xf5/0x140 mm/kasan/common.c:455
__cache_free mm/slab.c:3426 [inline]
kfree+0x103/0x2c0 mm/slab.c:3757
skb_free_head net/core/skbuff.c:590 [inline]
skb_release_data+0x6d9/0x910 net/core/skbuff.c:610
skb_release_all net/core/skbuff.c:664 [inline]
__kfree_skb net/core/skbuff.c:678 [inline]
consume_skb net/core/skbuff.c:837 [inline]
consume_skb+0xc2/0x160 net/core/skbuff.c:831
netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
netlink_unicast+0x53b/0x7d0 net/netlink/af_netlink.c:1329
netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1918
sock_sendmsg_nosec net/socket.c:652 [inline]
sock_sendmsg+0xcf/0x120 net/socket.c:672
____sys_sendmsg+0x6e8/0x810 net/socket.c:2352
___sys_sendmsg+0xf3/0x170 net/socket.c:2406
__sys_sendmsg+0xe5/0x1b0 net/socket.c:2439
do_syscall_64+0x60/0xe0 arch/x86/entry/common.c:359
entry_SYSCALL_64_after_hwframe+0x44/0xa9

The buggy address belongs to the object at ffff8880933b8c00
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 24 bytes inside of
512-byte region [ffff8880933b8c00, ffff8880933b8e00)
The buggy address belongs to the page:
page:ffffea00024cee00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea0002a1da08 ffffea0002763a08 ffff8880aa000a80
raw: 0000000000000000 ffff8880933b8000 0000000100000004 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff8880933b8b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff8880933b8b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff8880933b8c00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880933b8c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880933b8d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
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[Jason A. Donenfeld]

Hey Cong,

I'm wondering if the below error is related to what you've been
looking at yesterday. AFAICT, there's a simple UaF on the attrbuf
passed to the start method. I recall recently you were working on the
locking in genetlink's family buffers and wound up mallocing some
things, so it seems like this might be related. See below.

Regards,
Jason

[Cong Wang]

On Mon, Jun 29, 2020 at 6:17 PM Jason A. Donenfeld <Ja...@zx2c4.com> wrote:
>
> Hey Cong,

Hi, Jason

>
> I'm wondering if the below error is related to what you've been
> looking at yesterday. AFAICT, there's a simple UaF on the attrbuf
> passed to the start method. I recall recently you were working on the
> locking in genetlink's family buffers and wound up mallocing some
> things, so it seems like this might be related. See below.

Yeah, very likely it is the same bug I have fixed. I will close
this together with others.

Thanks.

[Cong Wang]

#syz fix: genetlink: get rid of family->attrbuf