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Date: Wed, 25 Jan 2023 01:17:10 -0800
From: Hyunwoo Kim <v4bel@...ori.io>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: davem@...emloft.net, edumazet@...gle.com, v4bel@...ori.io,
imv4bel@...il.com, kuba@...nel.org, linux-hams@...r.kernel.org,
netdev@...r.kernel.org, pabeni@...hat.com, ralf@...ux-mips.org,
syzbot+caa188bdfc1eeafeb418@...kaller.appspotmail.com
Subject: Re: [PATCH v2] netrom: Fix use-after-free caused by accept on
already connected socket
On Tue, Jan 24, 2023 at 05:43:47PM -0800, Kuniyuki Iwashima wrote:
> Hi,
>
> I think the diff looks good but changelog is not correct.
>
> From: Hyunwoo Kim <v4bel@...ori.io>
> Date: Mon, 23 Jan 2023 09:22:33 -0800
> > If listen() and accept() are called on an AF_NETROM socket that
> > has already been connect()ed, accept() succeeds in connecting.
> > This is because nr_accept() dequeues the skb queued in
> > `sk->sk_receive_queue` in nr_connect().
>
> This sentence is misleading. The skb sent by nr_connect() is queued
> up for the peer's sk_receive_queue (socket_2 below), and also the reply
> is not queued for connect()er (socket_1) because it is NR_CONNACK and
> just consumed by nr_state1_machine() to transition to NR_STATE_3 and
> TCP_ESTABLISHED.
>
>
> >
> > This causes nr_accept() to allocate and return a sock with the
> > sk of the parent AF_NETROM socket.
>
> This happens because the peer (socket_2) sends some data by nr_sendmsg(),
> whose type is NR_INFO and the data is queued up for the connect()er's
> (socket_1) sk_receive_queue by
>
> - nr_state3_machine
> - nr_queue_rx_frame
> - sock_queue_rcv_skb
you're right.
I misanalyzed nr_rx_frame(). sorry.
>
>
> > And here's where 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) // loopback connection with socket_1
> > 2. socket_1 = socket(AF_NETROM)
> > nr_create() // sk refcount : 1
> > connect(socket_1) // loopback connection with socket_2
> > nr_connect()
> > nr_establish_data_link()
> > nr_write_internal()
>
> This is NR_CONNREQ for socket_2.
>
>
> > nr_transmit_buffer()
> > nr_route_frame()
> > nr_loopback_queue()
> > nr_loopback_timer()
> > nr_rx_frame()
> > nr_process_rx_frame()
>
> So, nr_process_rx_frame() is not called from nr_rx_frame() because the
> kernel finds socket_2 by nr_find_listener(), and creates accepted_socket,
> and then responds with NR_CONNACK to socket_1.
>
> And accepted_socket sends some data with NR_INFO, then, nr_state3_machine()
> is called for socket_1 and the skb with sk pointing socket_1 is queued for
> socket_1's sk_receive_queue.
>
> I think this part is lacking in this UAF scenario.
>
> What do you think ?
>
>
> > 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 : sk->sk_receive_queue
> >
> > 3. listen(socket_1)
> > nr_listen()
> > uaf_socket = accept(socket_1)
> > nr_accept()
> > skb_dequeue(&sk->sk_receive_queue);
> > 4. close(accepted_socket)
>
> And I guess this close() is not so important in this case.
> Even if we don't close the socket cleanly, the UAF will happen, right ?
> (it might be caused in a different place like timer though)
IMHO, I think this `close(accepted_socket)` is a necessary procedure.
This is because `case NR_STATE_3:` in nr_release() is executed here,
and nr_write_internal(sk, NR_DISCREQ) ~ nr_disconnect() sets socket_1's sk to NR_STATE_0.
If sk of socket_1 is not set to NR_STATE_0, `case NR_STATE_3:` is executed instead of
`case NR_STATE_0:` in `close(socket_1)` and sk is not released.
This means you will not be able to trigger UAF on close(uaf_socket).
What do you think?
So the modified flow chart looks like this:
```
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)
nr_connect()
nr_establish_data_link()
nr_write_internal()
nr_transmit_buffer()
nr_route_frame()
nr_loopback_queue()
nr_loopback_timer()
nr_rx_frame()
nr_process_rx_frame()
nr_state1_machine()
nr->state = NR_STATE_3;
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_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
```
Anything wrong?
>
> > 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;
> > 5. 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 problem, nr_listen() returns -EINVAL for sockets that successfully nr_connect().
> >
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Reported-by: syzbot+caa188bdfc1eeafeb418@...kaller.appspotmail.com
> > Signed-off-by: Hyunwoo Kim <v4bel@...ori.io>
> > ---
> > net/netrom/af_netrom.c | 5 +++++
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/net/netrom/af_netrom.c b/net/netrom/af_netrom.c
> > index 6f7f4392cffb..5a4cb796150f 100644
> > --- a/net/netrom/af_netrom.c
> > +++ b/net/netrom/af_netrom.c
> > @@ -400,6 +400,11 @@ static int nr_listen(struct socket *sock, int backlog)
> > struct sock *sk = sock->sk;
> >
> > lock_sock(sk);
> > + if (sock->state != SS_UNCONNECTED) {
> > + release_sock(sk);
> > + return -EINVAL;
> > + }
> > +
> > if (sk->sk_state != TCP_LISTEN) {
> > memset(&nr_sk(sk)->user_addr, 0, AX25_ADDR_LEN);
> > sk->sk_max_ack_backlog = backlog;
> > --
> > 2.25.1
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