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

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

[Ding Hui]

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().

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@sangfor.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

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

[Chuck Lever III]

> On May 7, 2023, at 5:11 AM, Ding Hui <dinghui@sangfor.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@sangfor.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

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

[Ding Hui]

On 2023/5/7 23:26, Chuck Lever III wrote:
> 
> 
>> On May 7, 2023, at 5:11 AM, Ding Hui <dinghui@sangfor.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.
> 

I checked the vmcore, found that sk_odata points to sock_def_readable(),
and the sk_wq of newsock is NULL, which be assigned by sk_clone_lock()
unconditionally.

Calling sk_odata() for the newsock maybe do not wake up any sleepers.

> 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.
> 

Agree, but I don't have a good way for now.

> 
>> 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@sangfor.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
> 
> 
> 

-- 
Thanks,
- Ding Hui

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

[Chuck Lever III]

> On May 7, 2023, at 5:11 AM, Ding Hui <dinghui@sangfor.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@sangfor.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

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

[Chuck Lever III]

> On May 7, 2023, at 6:32 PM, Ding Hui <dinghui@sangfor.com.cn> wrote:
> 
> On 2023/5/7 23:26, Chuck Lever III wrote:
>>> On May 7, 2023, at 5:11 AM, Ding Hui <dinghui@sangfor.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.
> 
> I checked the vmcore, found that sk_odata points to sock_def_readable(),
> and the sk_wq of newsock is NULL, which be assigned by sk_clone_lock()
> unconditionally.
> 
> Calling sk_odata() for the newsock maybe do not wake up any sleepers.
> 
>> 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.
> 
> Agree, but I don't have a good way for now.

Would a smartly-placed svc_xprt_get() hold the listener in place
until accept processing completes?


>>> 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@sangfor.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
> 
> -- 
> Thanks,
> - Ding Hui


--
Chuck Lever

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

[Ding Hui]

On 2023/5/8 12:00, Chuck Lever III wrote:
> 
> 
>> On May 7, 2023, at 6:32 PM, Ding Hui <dinghui@sangfor.com.cn> wrote:
>>
>> On 2023/5/7 23:26, Chuck Lever III wrote:
>>>> On May 7, 2023, at 5:11 AM, Ding Hui <dinghui@sangfor.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.
>>
>> I checked the vmcore, found that sk_odata points to sock_def_readable(),
>> and the sk_wq of newsock is NULL, which be assigned by sk_clone_lock()
>> unconditionally.
>>
>> Calling sk_odata() for the newsock maybe do not wake up any sleepers.
>>
>>> 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.
>>
>> Agree, but I don't have a good way for now.
> 
> Would a smartly-placed svc_xprt_get() hold the listener in place
> until accept processing completes?
> 

It is difficult and complicated to me. I think it's a little bit out of
SUNRPC's control for the newsocks before accepted, e.g.: we don't know
how many they have.

Back to this RFC, I checked the code and thought it is safe by skipping
sk_odata() for the newsocks before accepted in **svc_tcp_listen_data_ready()**,
since these newsocks's sk_wq must be NULL, and will be assigned new one in
sock_alloc_inode() called by kernel_accept(), so we can say if the child sock
is not be accepted, there is nothing to be waked up.

> 
>>>> Reproduce by two tasks:
>>>> ...

-- 
Thanks,
- Ding Hui

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

[Chuck Lever III]

[ Removing the stale address for Bruce from the Cc, as he no longer
  works at Red Hat. ]


> On May 7, 2023, at 9:32 PM, Ding Hui <dinghui@sangfor.com.cn> wrote:
> 
> On 2023/5/7 23:26, Chuck Lever III wrote:
>>> On May 7, 2023, at 5:11 AM, Ding Hui <dinghui@sangfor.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.
> 
> I checked the vmcore, found that sk_odata points to sock_def_readable(),
> and the sk_wq of newsock is NULL, which be assigned by sk_clone_lock()
> unconditionally.
> 
> Calling sk_odata() for the newsock maybe do not wake up any sleepers.
> 
>> 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.
> 
> Agree, but I don't have a good way for now.
> 
>>> 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 haven't been able to reproduce a crash with this snippet. But
I've done some archaeology to understand the problem better.

I found that svc_tcp_listen_data_ready is actually invoked /three/
times: once for the listener socket, and /twice/ for the child.
The big comment, which pre-dates the git era, appears to be
somewhat stale; or perhaps it's the specifics of this particular
test that triggers the third call.

I reviewed several other tcp_listen_data_ready callbacks. They
generally do not do anything at all with non-listener sockets,
suggesting that approach would likely be safe for NFSD.

Prior to commit 939bb7ef901b ("[PATCH] Code cleanups in calbacks
in svcsock"), this data_ready callback was a complete no-op for
non-listener sockets as well. That commit is described as only
a clean-up, but it indeed changes the logic.

I also note that most other data_ready callbacks take the
sk_callback_lock, and svc_tcp_listen_data_ready does not. Not
clear to me whether svc_tcp_listen_data_ready should be taking
that lock too.

The upshot is that I think it would be reasonable to simply do
nothing in svc_tcp_listen_data_ready() if state != TCP_LISTEN.


>>> 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@sangfor.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
> 
> -- 
> Thanks,
> - Ding Hui
> 

--
Chuck Lever

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

[Ding Hui]

On 2023/5/15 2:29, Chuck Lever III wrote:
> [ Removing the stale address for Bruce from the Cc, as he no longer
>    works at Red Hat. ]
> 
> 
>> On May 7, 2023, at 9:32 PM, Ding Hui <dinghui@sangfor.com.cn> wrote:
>>
>> On 2023/5/7 23:26, Chuck Lever III wrote:
>>>> On May 7, 2023, at 5:11 AM, Ding Hui <dinghui@sangfor.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.
>>
>> I checked the vmcore, found that sk_odata points to sock_def_readable(),
>> and the sk_wq of newsock is NULL, which be assigned by sk_clone_lock()
>> unconditionally.
>>
>> Calling sk_odata() for the newsock maybe do not wake up any sleepers.
>>
>>> 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.
>>
>> Agree, but I don't have a good way for now.
>>
>>>> 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 haven't been able to reproduce a crash with this snippet. But

KASAN report should be easier to reproduce than real crash.

> I've done some archaeology to understand the problem better.
> 
> I found that svc_tcp_listen_data_ready is actually invoked /three/
> times: once for the listener socket, and /twice/ for the child.
> The big comment, which pre-dates the git era, appears to be
> somewhat stale; or perhaps it's the specifics of this particular
> test that triggers the third call.
> 
> I reviewed several other tcp_listen_data_ready callbacks. They
> generally do not do anything at all with non-listener sockets,
> suggesting that approach would likely be safe for NFSD.
> 
> Prior to commit 939bb7ef901b ("[PATCH] Code cleanups in calbacks
> in svcsock"), this data_ready callback was a complete no-op for
> non-listener sockets as well. That commit is described as only
> a clean-up, but it indeed changes the logic.
> 
> I also note that most other data_ready callbacks take the
> sk_callback_lock, and svc_tcp_listen_data_ready does not. Not
> clear to me whether svc_tcp_listen_data_ready should be taking
> that lock too.
> 

I notice the lock too, IMO the sk_callback_lock should be used
to protect the svsk avoiding be freed during in the callbacks.

Perhaps it can be reproduced by increasing the processing time in
svc_tcp_listen_data_ready(), but anyway, it would be another issue.

> The upshot is that I think it would be reasonable to simply do
> nothing in svc_tcp_listen_data_ready() if state != TCP_LISTEN.
> 

Thanks for the information.

I will send the formal patch soon later.

-- 
Thanks,
- Ding Hui