[master] 1d140b1a0 vca: Prevent conceptual workspace use-after-release

[Dridi Boukelmoune]

commit 1d140b1a09588c31583fbb6ae7ca6e3f626bb419
Author: Dridi Boukelmoune <dridi.boukelmoune at gmail.com>
Date:   Wed Jul 7 18:35:42 2021 +0200

    vca: Prevent conceptual workspace use-after-release
    
    Releasing a reservation or rolling back too early is harmless as long as
    nothing is allocated on the workspace that could overwrite its contents.
    
    Once you swap the workspace in its current form with a different kind of
    allocator it can turn into effective use-after-free, if rolled back or
    released state doesn't linger.

diff --git a/bin/varnishd/cache/cache_acceptor.c b/bin/varnishd/cache/cache_acceptor.c
index a57978e6a..33dc99130 100644
--- a/bin/varnishd/cache/cache_acceptor.c
+++ b/bin/varnishd/cache/cache_acceptor.c
@@ -400,8 +400,6 @@ vca_make_session(struct worker *wrk, void *arg)
 	    raddr, rport, wa->acceptlsock->name, laddr, lport,
 	    sp->t_open, sp->fd);
 
-	WS_Release(wrk->aws, 0);
-
 	vca_pace_good();
 	wrk->stats->sess_conn++;
 
@@ -416,6 +414,7 @@ vca_make_session(struct worker *wrk, void *arg)
 	req->htc->rfd = &sp->fd;
 
 	SES_SetTransport(wrk, sp, req, wa->acceptlsock->transport);
+	WS_Release(wrk->aws, 0);
 }
 
 /*--------------------------------------------------------------------