Re: [PATCH] SUNRPC: Fix UAF in svc_tcp_listen_data_ready()

On 2023/5/15 20:01, Chuck Lever III wrote:

...

On May 14, 2023, at 10:13 PM, Ding Hui dinghui@sangfor.com.cn wrote:

After the listener svc_sock be freed, and before invoking svc_tcp_accept() for the established child sock, there is a window that the newsock retaining a freed listener svc_sock in sk_user_data which cloning from parent.

Thank you, I will apply this (after testing it).

The next step is to figure out why SUNRPC is trying to accept on a dead listener. Any thoughts about that?

A child sock is cloned from the listener sock, it inherits sk_data_ready and sk_user_data from its parent sock, which is svc_tcp_listen_data_ready() and listener svc_sock, the sk_state of the child becomes ESTABLISHED once after TCP handshake in protocol stack.

Case 1:

listener sock | child sock | nfsd thread =>sk_data_ready | =>sk_data_ready | -------------------+-----------------------+---------------------- svc_tcp_listen_data_ready svsk is listener svc_sock set_bit(XPT_CONN) svc_recv svc_tcp_accept(listener) kernel_accept get child sock as newsock svc_setup_socket(newsock) newsock->sk_data_ready=svc_data_ready newsock->sk_user_data=newsvsk svc_data_ready svsk is newsvsk

Case 2:

listener sock | child sock | nfsd thread =>sk_data_ready | =>sk_data_ready | -------------------+-----------------------+---------------------- svc_tcp_listen_data_ready svsk is listener svc_sock set_bit(XPT_CONN) svc_tcp_listen_data_ready svsk is listener svc_sock svc_recv svc_tcp_accept(listener) kernel_accept get the child sock as newsock svc_setup_socket(newsock) newsock->sk_data_ready=svc_data_ready newsock->sk_user_data=newsvsk svc_data_ready svsk is newsvsk

The UAF case:

listener sock | child sock | rpc.nfsd 0 =>sk_data_ready | =>sk_data_ready | -------------------+-----------------------+---------------------- svc_tcp_listen_data_ready svsk is listener svc_sock set_bit(XPT_CONN) svc_xprt_destroy_all svc_xprt_free kfree listener svc_sock // the child sock has not yet been accepted, // so it is not managed by SUNRPC for now. svc_tcp_listen_data_ready svsk is listener svc_sock svsk->sk_odata // UAF!

...

In the race windows if data is received on the newsock, we will observe use-after-free report in svc_tcp_listen_data_ready().

Reproduce by two tasks:

1. while :; do rpc.nfsd 0 ; rpc.nfsd; done
2. while :; do echo "" | ncat -4 127.0.0.1 2049 ; done

I will continue attempting to reproduce, as I would like a root cause for this issue.

...

KASAN report:

================================================================== BUG: KASAN: slab-use-after-free in svc_tcp_listen_data_ready+0x1cf/0x1f0 [sunrpc] Read of size 8 at addr ffff888139d96228 by task nc/102553 CPU: 7 PID: 102553 Comm: nc Not tainted 6.3.0+ #18 Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020 Call Trace:

<IRQ> dump_stack_lvl+0x33/0x50 print_address_description.constprop.0+0x27/0x310 print_report+0x3e/0x70 kasan_report+0xae/0xe0 svc_tcp_listen_data_ready+0x1cf/0x1f0 [sunrpc] tcp_data_queue+0x9f4/0x20e0 tcp_rcv_established+0x666/0x1f60 tcp_v4_do_rcv+0x51c/0x850 tcp_v4_rcv+0x23fc/0x2e80 ip_protocol_deliver_rcu+0x62/0x300 ip_local_deliver_finish+0x267/0x350 ip_local_deliver+0x18b/0x2d0 ip_rcv+0x2fb/0x370 __netif_receive_skb_one_core+0x166/0x1b0 process_backlog+0x24c/0x5e0 __napi_poll+0xa2/0x500 net_rx_action+0x854/0xc90 __do_softirq+0x1bb/0x5de do_softirq+0xcb/0x100 </IRQ> <TASK> ... </TASK>

Allocated by task 102371: kasan_save_stack+0x1e/0x40 kasan_set_track+0x21/0x30 __kasan_kmalloc+0x7b/0x90 svc_setup_socket+0x52/0x4f0 [sunrpc] svc_addsock+0x20d/0x400 [sunrpc] __write_ports_addfd+0x209/0x390 [nfsd] write_ports+0x239/0x2c0 [nfsd] nfsctl_transaction_write+0xac/0x110 [nfsd] vfs_write+0x1c3/0xae0 ksys_write+0xed/0x1c0 do_syscall_64+0x38/0x90 entry_SYSCALL_64_after_hwframe+0x72/0xdc

Freed by task 102551: kasan_save_stack+0x1e/0x40 kasan_set_track+0x21/0x30 kasan_save_free_info+0x2a/0x50 __kasan_slab_free+0x106/0x190 __kmem_cache_free+0x133/0x270 svc_xprt_free+0x1e2/0x350 [sunrpc] svc_xprt_destroy_all+0x25a/0x440 [sunrpc] nfsd_put+0x125/0x240 [nfsd] nfsd_svc+0x2cb/0x3c0 [nfsd] write_threads+0x1ac/0x2a0 [nfsd] nfsctl_transaction_write+0xac/0x110 [nfsd] vfs_write+0x1c3/0xae0 ksys_write+0xed/0x1c0 do_syscall_64+0x38/0x90 entry_SYSCALL_64_after_hwframe+0x72/0xdc

Fix the UAF by simply doing nothing in svc_tcp_listen_data_ready() if state != TCP_LISTEN, that will avoid dereferencing svsk for all child socket.

Link: https://lore.kernel.org/lkml/20230507091131.23540-1-dinghui@sangfor.com.cn/ Fixes: fa9251afc33c ("SUNRPC: Call the default socket callbacks instead of open coding") Signed-off-by: Ding Hui dinghui@sangfor.com.cn Cc: stable@vger.kernel.org

---

net/sunrpc/svcsock.c | 23 +++++++++++------------ 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c index a51c9b989d58..9aca6e1e78e4 100644 --- a/net/sunrpc/svcsock.c +++ b/net/sunrpc/svcsock.c @@ -825,12 +825,6 @@ static void svc_tcp_listen_data_ready(struct sock *sk)

trace_sk_data_ready(sk);

• if (svsk) {
• /* Refer to svc_setup_socket() for details. */
• rmb();
• svsk->sk_odata(sk);
• }

/*

• This callback may called twice when a new connection
• is established as a child socket inherits everything

@@ -839,13 +833,18 @@ static void svc_tcp_listen_data_ready(struct sock *sk)

• when one of child sockets become ESTABLISHED.
• 2. data_ready method of the child socket may be called
• when it receives data before the socket is accepted.

• • In case of 2, we should ignore it silently.

• • In case of 2, we should ignore it silently and DO NOT
• • dereference svsk.

*/

• if (sk->sk_state == TCP_LISTEN) {
• if (svsk) {
• set_bit(XPT_CONN, &svsk->sk_xprt.xpt_flags);
• svc_xprt_enqueue(&svsk->sk_xprt);
• }

• if (sk->sk_state != TCP_LISTEN)
• return;
• if (svsk) {
• /* Refer to svc_setup_socket() for details. */
• rmb();
• svsk->sk_odata(sk);
• set_bit(XPT_CONN, &svsk->sk_xprt.xpt_flags);
• svc_xprt_enqueue(&svsk->sk_xprt);

} }

-- 2.17.1

-- Chuck Lever