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Message-ID: <EED05302-8BC6-4593-B798-BFC476FA190E@oracle.com>
Date: Sun, 7 May 2023 15:26:49 +0000
From: Chuck Lever III <chuck.lever@...cle.com>
To: Ding Hui <dinghui@...gfor.com.cn>
CC: "jlayton@...nel.org" <jlayton@...nel.org>,
"trond.myklebust@...merspace.com" <trond.myklebust@...merspace.com>,
"anna@...nel.org" <anna@...nel.org>,
"davem@...emloft.net" <davem@...emloft.net>,
"edumazet@...gle.com" <edumazet@...gle.com>,
"kuba@...nel.org" <kuba@...nel.org>,
"pabeni@...hat.com" <pabeni@...hat.com>,
Bruce Fields <bfields@...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>
Subject: Re: [RFC PATCH] SUNRPC: Fix UAF in svc_tcp_listen_data_ready()
> On May 7, 2023, at 5:11 AM, Ding Hui <dinghui@...gfor.com.cn> wrote:
>
> After the listener svc_sock 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. In the race windows if data is received on the newsock, we will
> observe use-after-free report in svc_tcp_listen_data_ready().
My thought is that not calling sk_odata() for the newsock
could potentially result in missing a data_ready event,
resulting in a hung client on that socket.
IMO the preferred approach is to ensure that svsk is always
safe to dereference in tcp_listen_data_ready. I haven't yet
thought carefully about how to do that.
> 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
>
> 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
>
> In this RFC patch, I try to fix the UAF by skipping dereferencing
> svsk for all child socket in svc_tcp_listen_data_ready(), it is
> easy to backport for stable.
>
> However I'm not sure if there are other potential risks in the race
> window, so I thought another fix which depends on SK_USER_DATA_NOCOPY
> introduced in commit f1ff5ce2cd5e ("net, sk_msg: Clear sk_user_data
> pointer on clone if tagged").
>
> Saving svsk into sk_user_data with SK_USER_DATA_NOCOPY tag in
> svc_setup_socket() like this:
>
> __rcu_assign_sk_user_data_with_flags(inet, svsk, SK_USER_DATA_NOCOPY);
>
> Obtaining svsk in callbacks like this:
>
> struct svc_sock *svsk = rcu_dereference_sk_user_data(sk);
>
> This will avoid copying sk_user_data for sunrpc svc_sock in
> sk_clone_lock(), so the sk_user_data of child sock before accepted
> will be NULL.
>
> Appreciate any comment and suggestion, thanks.
>
> Fixes: fa9251afc33c ("SUNRPC: Call the default socket callbacks instead of open coding")
> Signed-off-by: Ding Hui <dinghui@...gfor.com.cn>
> ---
> 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
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