• Hyunwoo Kim's avatar
    netrom: Fix use-after-free caused by accept on already connected socket · 61179292
    Hyunwoo Kim authored
    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: default avatarHyunwoo Kim <v4bel@theori.io>
    Reviewed-by: default avatarKuniyuki Iwashima <kuniyu@amazon.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    61179292
af_netrom.c 32.5 KB