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Date: Mon, 15 May 2023 22:55:11 +0800
From: Ding Hui <dinghui@...gfor.com.cn>
To: Chuck Lever III <chuck.lever@...cle.com>
Cc: Jeff Layton <jlayton@...nel.org>,
Trond Myklebust <trond.myklebust@...merspace.com>,
Anna Schumaker <anna@...nel.org>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: 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@...gfor.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@...gfor.com.cn>
>> Cc: <stable@...r.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
>
>
>
--
Thanks,
-dinghui
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