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BUG: KASAN: use-after-free in atomic_read include/asm-generic/atomic-instrumented.h:21 [inline]
BUG: KASAN: use-after-free in refcount_dec_not_one+0x71/0x1d0 lib/refcount.c:269
Read of size 4 at addr ffff88809dfe0dd8 by task syz-executor742/9210

CPU: 0 PID: 9210 Comm: syz-executor742 Not tainted 4.19.211-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+0x1fc/0x2ef lib/dump_stack.c:118
 print_address_description.cold+0x54/0x219 mm/kasan/report.c:256
 kasan_report_error.cold+0x8a/0x1b9 mm/kasan/report.c:354
 kasan_report+0x8f/0xa0 mm/kasan/report.c:412
 atomic_read include/asm-generic/atomic-instrumented.h:21 [inline]
 refcount_dec_not_one+0x71/0x1d0 lib/refcount.c:269
 refcount_dec_and_mutex_lock+0x1c/0x80 lib/refcount.c:308
 nbd_put drivers/block/nbd.c:228 [inline]
 nbd_genl_connect+0x11ee/0x1630 drivers/block/nbd.c:1913
 genl_family_rcv_msg+0x642/0xc40 net/netlink/genetlink.c:602
 genl_rcv_msg+0xbf/0x160 net/netlink/genetlink.c:627
 netlink_rcv_skb+0x160/0x440 net/netlink/af_netlink.c:2463
 genl_rcv+0x24/0x40 net/netlink/genetlink.c:638
 netlink_unicast_kernel net/netlink/af_netlink.c:1325 [inline]
 netlink_unicast+0x4d5/0x690 net/netlink/af_netlink.c:1351
 netlink_sendmsg+0x6c3/0xc50 net/netlink/af_netlink.c:1917
 sock_sendmsg_nosec net/socket.c:651 [inline]
 sock_sendmsg+0xc3/0x120 net/socket.c:661
 ___sys_sendmsg+0x7bb/0x8e0 net/socket.c:2227
 __sys_sendmsg net/socket.c:2265 [inline]
 __do_sys_sendmsg net/socket.c:2274 [inline]
 __se_sys_sendmsg net/socket.c:2272 [inline]
 __x64_sys_sendmsg+0x132/0x220 net/socket.c:2272
 do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x7fa390b69839
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 14 00 00 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 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe2b7b1b08 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 000000000000a080 RCX: 00007fa390b69839
RDX: 0000000000000000 RSI: 0000000020000380 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: 00007ffe2b7b1ca8
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffe2b7b1b1c
R13: 431bde82d7b634db R14: 0000000000000000 R15: 0000000000000000

Allocated by task 9205:
 kmem_cache_alloc_trace+0x12f/0x380 mm/slab.c:3625
 kmalloc include/linux/slab.h:515 [inline]
 kzalloc include/linux/slab.h:709 [inline]
 nbd_dev_add+0x44/0x890 drivers/block/nbd.c:1627
 nbd_genl_connect+0x4cc/0x1630 drivers/block/nbd.c:1773
 genl_family_rcv_msg+0x642/0xc40 net/netlink/genetlink.c:602
 genl_rcv_msg+0xbf/0x160 net/netlink/genetlink.c:627
 netlink_rcv_skb+0x160/0x440 net/netlink/af_netlink.c:2463
 genl_rcv+0x24/0x40 net/netlink/genetlink.c:638
 netlink_unicast_kernel net/netlink/af_netlink.c:1325 [inline]
 netlink_unicast+0x4d5/0x690 net/netlink/af_netlink.c:1351
 netlink_sendmsg+0x6c3/0xc50 net/netlink/af_netlink.c:1917
 sock_sendmsg_nosec net/socket.c:651 [inline]
 sock_sendmsg+0xc3/0x120 net/socket.c:661
 ___sys_sendmsg+0x7bb/0x8e0 net/socket.c:2227
 __sys_sendmsg net/socket.c:2265 [inline]
 __do_sys_sendmsg net/socket.c:2274 [inline]
 __se_sys_sendmsg net/socket.c:2272 [inline]
 __x64_sys_sendmsg+0x132/0x220 net/socket.c:2272
 do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Freed by task 9210:
 __cache_free mm/slab.c:3503 [inline]
 kfree+0xcc/0x210 mm/slab.c:3822
 nbd_dev_remove drivers/block/nbd.c:223 [inline]
 nbd_put.part.0+0xfe/0x140 drivers/block/nbd.c:231
 nbd_put drivers/block/nbd.c:275 [inline]
 nbd_config_put+0x6a0/0x870 drivers/block/nbd.c:1185
 nbd_genl_connect+0x11bb/0x1630 drivers/block/nbd.c:1911
 genl_family_rcv_msg+0x642/0xc40 net/netlink/genetlink.c:602
 genl_rcv_msg+0xbf/0x160 net/netlink/genetlink.c:627
 netlink_rcv_skb+0x160/0x440 net/netlink/af_netlink.c:2463
 genl_rcv+0x24/0x40 net/netlink/genetlink.c:638
 netlink_unicast_kernel net/netlink/af_netlink.c:1325 [inline]
 netlink_unicast+0x4d5/0x690 net/netlink/af_netlink.c:1351
 netlink_sendmsg+0x6c3/0xc50 net/netlink/af_netlink.c:1917
 sock_sendmsg_nosec net/socket.c:651 [inline]
 sock_sendmsg+0xc3/0x120 net/socket.c:661
 ___sys_sendmsg+0x7bb/0x8e0 net/socket.c:2227
 __sys_sendmsg net/socket.c:2265 [inline]
 __do_sys_sendmsg net/socket.c:2274 [inline]
 __se_sys_sendmsg net/socket.c:2272 [inline]
 __x64_sys_sendmsg+0x132/0x220 net/socket.c:2272
 do_syscall_64+0xf9/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

The buggy address belongs to the object at ffff88809dfe0d00
 which belongs to the cache kmalloc-512 of size 512
The buggy address is located 216 bytes inside of
 512-byte region [ffff88809dfe0d00, ffff88809dfe0f00)
The buggy address belongs to the page:
page:ffffea000277f800 count:1 mapcount:0 mapping:ffff88813bff0940 index:0x0
flags: 0xfff00000000100(slab)
raw: 00fff00000000100 ffffea0002930948 ffffea00026ccfc8 ffff88813bff0940
raw: 0000000000000000 ffff88809dfe0080 0000000100000006 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff88809dfe0c80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88809dfe0d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88809dfe0d80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                    ^
 ffff88809dfe0e00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88809dfe0e80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
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