On Wed, Jan 25, 2023 at 08:40:35AM -0800, Kuniyuki Iwashima wrote:

From:   Hyunwoo Kim <redacted>
Date:   Wed, 25 Jan 2023 01:17:10 -0800

quoted

On Tue, Jan 24, 2023 at 05:43:47PM -0800, Kuniyuki Iwashima wrote:

quoted

Hi,

I think the diff looks good but changelog is not correct.

From:   Hyunwoo Kim <redacted>
Date:   Mon, 23 Jan 2023 09:22:33 -0800

quoted

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.

quoted

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.

quoted

quoted

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.

quoted

            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 ?

quoted

            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.

No, it's released by the heartbeat timer.  The heartbeat timer finally
calls nr_destroy_socket() as SOCK_DESTROY is flagged to the sk.

quoted

This means you will not be able to trigger UAF on close(uaf_socket).

I didn't say close(uaf_socket) is not needed, I mean we can
trigger UAF without close(__accepted_socket__).

ok. understand. The reason why I put close(accepted_socket) 
is because Freed by task in the KASAN log I attached to the 
patch description is as follows:

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

If, as you say, heartbeat is running and UAF is triggered, 
the KASAN Freed log will look like this:

Freed by task 14094:
 kasan_save_stack+0x22/0x40 mm/kasan/common.c:45
 kasan_set_track+0x25/0x30 mm/kasan/common.c:52
 kasan_save_free_info+0x2e/0x40 mm/kasan/generic.c:518
 ____kasan_slab_free mm/kasan/common.c:236 [inline]
 ____kasan_slab_free+0x160/0x1c0 mm/kasan/common.c:200
 kasan_slab_free include/linux/kasan.h:177 [inline]
 slab_free_hook mm/slub.c:1781 [inline]
 slab_free_freelist_hook+0x8b/0x1c0 mm/slub.c:1807
 slab_free mm/slub.c:3787 [inline]
 __kmem_cache_free+0xaf/0x3b0 mm/slub.c:3800
 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_heartbeat_expiry+0x1d7/0x460 net/netrom/nr_timer.c:148
 call_timer_fn+0x1da/0x7c0 kernel/time/timer.c:1700
 expire_timers+0x2c6/0x5c0 kernel/time/timer.c:1751
 __run_timers kernel/time/timer.c:2022 [inline]
 __run_timers kernel/time/timer.c:1995 [inline]
 run_timer_softirq+0x326/0x910 kernel/time/timer.c:2035
 __do_softirq+0x1fb/0xadc kernel/softirq.c:571

Anyway, I'm trying to keep close(accepted_socket) in the flow chart 
because the KASAN log I added to the first patch description is the first one.

quoted

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;

If you write the connect()'s stack trace, you should note the state
change at the socket_1 side by NR_CONNACK.  The NR_STATE_3 here is
for socket_2 by NR_CONNREQ.  We don't need the details of socket_2.

Otherwise, you should just write connect(socket_1) only like the
step 1 (socket(), listen() etc).

So, the modified flow chart is:

                  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

And sorry for sending the v3 netrom patch first. 
I received an email that the v2 x25 patch with the wrong patch 
description was applied to the tree, 
so I made a v3 x25 patch in a hurry and sent the netrom as well.

quoted

                                                               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@syzkaller.appspotmail.com
> > Signed-off-by: Hyunwoo Kim <v4bel@theori.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