On 2023/5/15 20:01, Chuck Lever III wrote:
On May 14, 2023, at 10:13 PM, Ding Hui <dinghui@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx/
Fixes: fa9251afc33c ("SUNRPC: Call the default socket callbacks instead of open coding")
Signed-off-by: Ding Hui <dinghui@xxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
---
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
