[PATCH] net/handshake: duplicate handshake cancellations leak socket

[PATCH] net/handshake: duplicate handshake cancellations leak socket

[Scott Mayhew]

When a handshake request is cancelled it is removed from the
handshake_net->hn_requests list, but it is still present in the
handshake_rhashtbl until it is destroyed.

If a second cancellation request arrives for the same handshake request,
then remove_pending() will return false... and assuming
HANDSHAKE_F_REQ_COMPLETED isn't set in req->hr_flags, we'll continue
processing through the out_true label, where we put another reference on
the sock and a refcount underflow occurs.

This can happen for example if a handshake times out - particularly if
the SUNRPC client sends the AUTH_TLS probe to the server but doesn't
follow it up with the ClientHello due to a problem with tlshd.  When the
timeout is hit on the server, the server will send a FIN, which triggers
a cancellation request via xs_reset_transport().  When the timeout is
hit on the client, another cancellation request happens via
xs_tls_handshake_sync().

Add a test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED) in the pending cancel
path so duplicate cancels can be detected.

Fixes: 3b3009ea8abb ("net/handshake: Create a NETLINK service for handling handshake requests")
Suggested-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Scott Mayhew <smayhew@redhat.com>
---
 net/handshake/request.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/net/handshake/request.c b/net/handshake/request.c
index 274d2c89b6b2..f78091680bca 100644
--- a/net/handshake/request.c
+++ b/net/handshake/request.c
@@ -324,7 +324,11 @@ bool handshake_req_cancel(struct sock *sk)
 
 	hn = handshake_pernet(net);
 	if (hn && remove_pending(hn, req)) {
-		/* Request hadn't been accepted */
+		/* Request hadn't been accepted - mark cancelled */
+		if (test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED, &req->hr_flags)) {
+			trace_handshake_cancel_busy(net, req, sk);
+			return false;
+		}
 		goto out_true;
 	}
 	if (test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED, &req->hr_flags)) {
-- 
2.51.0

Re: [PATCH] net/handshake: duplicate handshake cancellations leak socket

[Chuck Lever]

On Tue, Dec 9, 2025, at 2:30 PM, Scott Mayhew wrote:
> When a handshake request is cancelled it is removed from the
> handshake_net->hn_requests list, but it is still present in the
> handshake_rhashtbl until it is destroyed.
>
> If a second cancellation request arrives for the same handshake request,
> then remove_pending() will return false... and assuming
> HANDSHAKE_F_REQ_COMPLETED isn't set in req->hr_flags, we'll continue
> processing through the out_true label, where we put another reference on
> the sock and a refcount underflow occurs.
>
> This can happen for example if a handshake times out - particularly if
> the SUNRPC client sends the AUTH_TLS probe to the server but doesn't
> follow it up with the ClientHello due to a problem with tlshd.  When the
> timeout is hit on the server, the server will send a FIN, which triggers
> a cancellation request via xs_reset_transport().  When the timeout is
> hit on the client, another cancellation request happens via
> xs_tls_handshake_sync().
>
> Add a test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED) in the pending cancel
> path so duplicate cancels can be detected.
>
> Fixes: 3b3009ea8abb ("net/handshake: Create a NETLINK service for 
> handling handshake requests")
> Suggested-by: Chuck Lever <chuck.lever@oracle.com>
> Signed-off-by: Scott Mayhew <smayhew@redhat.com>
> ---
>  net/handshake/request.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/net/handshake/request.c b/net/handshake/request.c
> index 274d2c89b6b2..f78091680bca 100644
> --- a/net/handshake/request.c
> +++ b/net/handshake/request.c
> @@ -324,7 +324,11 @@ bool handshake_req_cancel(struct sock *sk)
> 
>  	hn = handshake_pernet(net);
>  	if (hn && remove_pending(hn, req)) {
> -		/* Request hadn't been accepted */
> +		/* Request hadn't been accepted - mark cancelled */
> +		if (test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED, &req->hr_flags)) {
> +			trace_handshake_cancel_busy(net, req, sk);
> +			return false;
> +		}
>  		goto out_true;
>  	}
>  	if (test_and_set_bit(HANDSHAKE_F_REQ_COMPLETED, &req->hr_flags)) {
> -- 
> 2.51.0

Reviewed-by: Chuck Lever <chuck.lever@oracle.com>


-- 
Chuck Lever

Re: [PATCH] net/handshake: duplicate handshake cancellations leak socket

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Paolo Abeni <pabeni@redhat.com>:

On Tue,  9 Dec 2025 14:30:15 -0500 you wrote:
> When a handshake request is cancelled it is removed from the
> handshake_net->hn_requests list, but it is still present in the
> handshake_rhashtbl until it is destroyed.
> 
> If a second cancellation request arrives for the same handshake request,
> then remove_pending() will return false... and assuming
> HANDSHAKE_F_REQ_COMPLETED isn't set in req->hr_flags, we'll continue
> processing through the out_true label, where we put another reference on
> the sock and a refcount underflow occurs.
> 
> [...]

Here is the summary with links:
  - net/handshake: duplicate handshake cancellations leak socket
    https://git.kernel.org/netdev/net/c/15564bd67e29

You are awesome, thank you!
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