netrom: Fix use-after-free caused by accept on already connected socket
If you call listen() and accept() on an already connect()ed
AF_NETROM socket, accept() can successfully connect.
This is because when the peer socket sends data to sendmsg,
the skb with its own sk stored in the connected socket's
sk->sk_receive_queue is connected, and nr_accept() dequeues
the skb waiting in the sk->sk_receive_queue.
As a result, nr_accept() allocates and returns a sock with
the sk of the parent AF_NETROM socket.
And here use-after-free can happen through complex race conditions:
```
cpu0 cpu1
1. socket_2 = socket(AF_NETROM)
.
.
listen(socket_2)
accepted_socket = accept(socket_2)
2. socket_1 = socket(AF_NETROM)
nr_create() // sk refcount : 1
connect(socket_1)
3. write(accepted_socket)
nr_sendmsg()
nr_output()
nr_kick()
nr_send_iframe()
nr_transmit_buffer()
nr_route_frame()
nr_loopback_queue()
nr_loopback_timer()
nr_rx_frame()
nr_process_rx_frame(sk, skb); // sk : socket_1's sk
nr_state3_machine()
nr_queue_rx_frame()
sock_queue_rcv_skb()
sock_queue_rcv_skb_reason()
__sock_queue_rcv_skb()
__skb_queue_tail(list, skb); // list : socket_1's sk->sk_receive_queue
4. listen(socket_1)
nr_listen()
uaf_socket = accept(socket_1)
nr_accept()
skb_dequeue(&sk->sk_receive_queue);
5. close(accepted_socket)
nr_release()
nr_write_internal(sk, NR_DISCREQ)
nr_transmit_buffer() // NR_DISCREQ
nr_route_frame()
nr_loopback_queue()
nr_loopback_timer()
nr_rx_frame() // sk : socket_1's sk
nr_process_rx_frame() // NR_STATE_3
nr_state3_machine() // NR_DISCREQ
nr_disconnect()
nr_sk(sk)->state = NR_STATE_0;
6. close(socket_1) // sk refcount : 3
nr_release() // NR_STATE_0
sock_put(sk); // sk refcount : 0
sk_free(sk);
close(uaf_socket)
nr_release()
sock_hold(sk); // UAF
```
KASAN report by syzbot:
```
BUG: KASAN: use-after-free in nr_release+0x66/0x460 net/netrom/af_netrom.c:520
Write of size 4 at addr ffff8880235d8080 by task syz-executor564/5128
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd1/0x138 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:306 [inline]
print_report+0x15e/0x461 mm/kasan/report.c:417
kasan_report+0xbf/0x1f0 mm/kasan/report.c:517
check_region_inline mm/kasan/generic.c:183 [inline]
kasan_check_range+0x141/0x190 mm/kasan/generic.c:189
instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
atomic_fetch_add_relaxed include/linux/atomic/atomic-instrumented.h:116 [inline]
__refcount_add include/linux/refcount.h:193 [inline]
__refcount_inc include/linux/refcount.h:250 [inline]
refcount_inc include/linux/refcount.h:267 [inline]
sock_hold include/net/sock.h:775 [inline]
nr_release+0x66/0x460 net/netrom/af_netrom.c:520
__sock_release+0xcd/0x280 net/socket.c:650
sock_close+0x1c/0x20 net/socket.c:1365
__fput+0x27c/0xa90 fs/file_table.c:320
task_work_run+0x16f/0x270 kernel/task_work.c:179
exit_task_work include/linux/task_work.h:38 [inline]
do_exit+0xaa8/0x2950 kernel/exit.c:867
do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
get_signal+0x21c3/0x2450 kernel/signal.c:2859
arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
__syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7f6c19e3c9b9
Code: Unable to access opcode bytes at 0x7f6c19e3c98f.
RSP: 002b:00007fffd4ba2ce8 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: 0000000000000116 RBX: 0000000000000003 RCX: 00007f6c19e3c9b9
RDX: 0000000000000318 RSI: 00000000200bd000 RDI: 0000000000000006
RBP: 0000000000000003 R08: 000000000000000d R09: 000000000000000d
R10: 0000000000000000 R11: 0000000000000246 R12: 000055555566a2c0
R13: 0000000000000011 R14: 0000000000000000 R15: 0000000000000000
</TASK>
Allocated by task 5128:
kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
kasan_set_track+0x25/0x30 mm/kasan/common.c:52
____kasan_kmalloc mm/kasan/common.c:371 [inline]
____kasan_kmalloc mm/kasan/common.c:330 [inline]
__kasan_kmalloc+0xa3/0xb0 mm/kasan/common.c:380
kasan_kmalloc include/linux/kasan.h:211 [inline]
__do_kmalloc_node mm/slab_common.c:968 [inline]
__kmalloc+0x5a/0xd0 mm/slab_common.c:981
kmalloc include/linux/slab.h:584 [inline]
sk_prot_alloc+0x140/0x290 net/core/sock.c:2038
sk_alloc+0x3a/0x7a0 net/core/sock.c:2091
nr_create+0xb6/0x5f0 net/netrom/af_netrom.c:433
__sock_create+0x359/0x790 net/socket.c:1515
sock_create net/socket.c:1566 [inline]
__sys_socket_create net/socket.c:1603 [inline]
__sys_socket_create net/socket.c:1588 [inline]
__sys_socket+0x133/0x250 net/socket.c:1636
__do_sys_socket net/socket.c:1649 [inline]
__se_sys_socket net/socket.c:1647 [inline]
__x64_sys_socket+0x73/0xb0 net/socket.c:1647
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x39/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x63/0xcd
Freed by task 5128:
kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
kasan_set_track+0x25/0x30 mm/kasan/common.c:52
kasan_save_free_info+0x2b/0x40 mm/kasan/generic.c:518
____kasan_slab_free mm/kasan/common.c:236 [inline]
____kasan_slab_free+0x13b/0x1a0 mm/kasan/common.c:200
kasan_slab_free include/linux/kasan.h:177 [inline]
__cache_free mm/slab.c:3394 [inline]
__do_kmem_cache_free mm/slab.c:3580 [inline]
__kmem_cache_free+0xcd/0x3b0 mm/slab.c:3587
sk_prot_free net/core/sock.c:2074 [inline]
__sk_destruct+0x5df/0x750 net/core/sock.c:2166
sk_destruct net/core/sock.c:2181 [inline]
__sk_free+0x175/0x460 net/core/sock.c:2192
sk_free+0x7c/0xa0 net/core/sock.c:2203
sock_put include/net/sock.h:1991 [inline]
nr_release+0x39e/0x460 net/netrom/af_netrom.c:554
__sock_release+0xcd/0x280 net/socket.c:650
sock_close+0x1c/0x20 net/socket.c:1365
__fput+0x27c/0xa90 fs/file_table.c:320
task_work_run+0x16f/0x270 kernel/task_work.c:179
exit_task_work include/linux/task_work.h:38 [inline]
do_exit+0xaa8/0x2950 kernel/exit.c:867
do_group_exit+0xd4/0x2a0 kernel/exit.c:1012
get_signal+0x21c3/0x2450 kernel/signal.c:2859
arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
__syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x63/0xcd
```
To fix this issue, nr_listen() returns -EINVAL for sockets that
successfully nr_connect().
Reported-by: syzbot+caa188bdfc1eeafeb418@syzkaller.appspotmail.com
Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: 
Hyunwoo Kim <v4bel@theori.io>
Reviewed-by: 
Kuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: 
David S. Miller <davem@davemloft.net>
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