From: Kuniyuki Iwashima kuniyu@amazon.com
[ Upstream commit 409db27e3a2eb5e8ef7226ca33be33361b3ed1c9 ]
syzbot reported a use-after-free in do_accept(), precisely nr_accept() as sk_prot_alloc() allocated the memory and sock_put() frees it. [0]
The issue could happen if the heartbeat timer is fired and nr_heartbeat_expiry() calls nr_destroy_socket(), where a socket has SOCK_DESTROY or a listening socket has SOCK_DEAD.
In this case, the first condition cannot be true. SOCK_DESTROY is flagged in nr_release() only when the file descriptor is close()d, but accept() is being called for the listening socket, so the second condition must be true.
Usually, the AF_NETROM listener neither starts timers nor sets SOCK_DEAD. However, the condition is met if connect() fails before listen(). connect() starts the t1 timer and heartbeat timer, and t1timer calls nr_disconnect() when timeout happens. Then, SOCK_DEAD is set, and if we call listen(), the heartbeat timer calls nr_destroy_socket().
nr_connect nr_establish_data_link(sk) nr_start_t1timer(sk) nr_start_heartbeat(sk) nr_t1timer_expiry nr_disconnect(sk, ETIMEDOUT) nr_sk(sk)->state = NR_STATE_0 sk->sk_state = TCP_CLOSE sock_set_flag(sk, SOCK_DEAD) nr_listen if (sk->sk_state != TCP_LISTEN) sk->sk_state = TCP_LISTEN nr_heartbeat_expiry switch (nr->state) case NR_STATE_0 if (sk->sk_state == TCP_LISTEN && sock_flag(sk, SOCK_DEAD)) nr_destroy_socket(sk)
This path seems expected, and nr_destroy_socket() is called to clean up resources. Initially, there was sock_hold() before nr_destroy_socket() so that the socket would not be freed, but the commit 517a16b1a88b ("netrom: Decrease sock refcount when sock timers expire") accidentally removed it.
To fix use-after-free, let's add sock_hold().
[0]: BUG: KASAN: use-after-free in do_accept+0x483/0x510 net/socket.c:1848 Read of size 8 at addr ffff88807978d398 by task syz-executor.3/5315
CPU: 0 PID: 5315 Comm: syz-executor.3 Not tainted 6.2.0-rc3-syzkaller-00165-gd9fc1511728c #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/26/2022 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 do_accept+0x483/0x510 net/socket.c:1848 __sys_accept4_file net/socket.c:1897 [inline] __sys_accept4+0x9a/0x120 net/socket.c:1927 __do_sys_accept net/socket.c:1944 [inline] __se_sys_accept net/socket.c:1941 [inline] __x64_sys_accept+0x75/0xb0 net/socket.c:1941 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 RIP: 0033:0x7fa436a8c0c9 Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 f1 19 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 b8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fa437784168 EFLAGS: 00000246 ORIG_RAX: 000000000000002b RAX: ffffffffffffffda RBX: 00007fa436bac050 RCX: 00007fa436a8c0c9 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000005 RBP: 00007fa436ae7ae9 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007ffebc6700df R14: 00007fa437784300 R15: 0000000000022000 </TASK>
Allocated by task 5294: 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 14: 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_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
Fixes: 517a16b1a88b ("netrom: Decrease sock refcount when sock timers expire") Reported-by: syzbot+5fafd5cfe1fc91f6b352@syzkaller.appspotmail.com Signed-off-by: Kuniyuki Iwashima kuniyu@amazon.com Link: https://lore.kernel.org/r/20230120231927.51711-1-kuniyu@amazon.com Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/netrom/nr_timer.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/net/netrom/nr_timer.c b/net/netrom/nr_timer.c index a8da88db7893..4e7c968cde2d 100644 --- a/net/netrom/nr_timer.c +++ b/net/netrom/nr_timer.c @@ -121,6 +121,7 @@ static void nr_heartbeat_expiry(struct timer_list *t) is accepted() it isn't 'dead' so doesn't get removed. */ if (sock_flag(sk, SOCK_DESTROY) || (sk->sk_state == TCP_LISTEN && sock_flag(sk, SOCK_DEAD))) { + sock_hold(sk); bh_unlock_sock(sk); nr_destroy_socket(sk); goto out;