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SubjectKASAN: use-after-free Read in devlink_get_from_attrs
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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=1048c3c5100000
kernel config: https://syzkaller.appspot.com/x/.config?x=bf3aec367b9ab569
dashboard link: https://syzkaller.appspot.com/bug?extid=09b4a3f42f32d58b8982
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=108b3df9100000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11d426e3100000

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+09b4a3f42f32d58b8982@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: use-after-free in strcmp+0x90/0xb0 lib/string.c:364
Read of size 1 at addr ffff88808408dc18 by task syz-executor100/8628

CPU: 0 PID: 8628 Comm: syz-executor100 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
strcmp+0x90/0xb0 lib/string.c:364
devlink_get_from_attrs+0x1bf/0x2f0 net/core/devlink.c:133
devlink_nl_cmd_region_read_dumpit+0x177/0xed0 net/core/devlink.c:4271
genl_lock_dumpit+0x7f/0xb0 net/netlink/genetlink.c:575
netlink_dump+0x4cd/0xf60 net/netlink/af_netlink.c:2245
__netlink_dump_start+0x643/0x900 net/netlink/af_netlink.c:2353
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: 0033:0x447c09
Code: Bad RIP value.
RSP: 002b:00007ffcadc8f968 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000447c09
RDX: 0000000000000000 RSI: 0000000020000380 RDI: 0000000000000003
RBP: 00000000000119d3 R08: 0000000000000000 R09: 0000000200000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000404ed0 R14: 0000000000000000 R15: 0000000000000000

Allocated by task 8626:
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 8626:
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 ffff88808408dc00
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 24 bytes inside of
512-byte region [ffff88808408dc00, ffff88808408de00)
The buggy address belongs to the page:
page:ffffea0002102340 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0
flags: 0xfffe0000000200(slab)
raw: 00fffe0000000200 ffffea00024d93c8 ffffea000211e048 ffff8880aa000a80
raw: 0000000000000000 ffff88808408d000 0000000100000004 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff88808408db00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88808408db80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88808408dc00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88808408dc80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88808408dd00: 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.
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syzbot can test patches for this bug, for details see:
https://goo.gl/tpsmEJ#testing-patches

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