BUG/MINOR: ssl: Prevent removal of crt-list line if the instance is a default one

If the first active line of a crt-list file is also the first mentioned
certificate of a frontend that does not have the strict-sni option
enabled, then its certificate will be used as the default one. We then
do not want this instance to be removable since it would make a frontend
lose its default certificate.
Considering that a crt-list file can be used by multiple frontends, and
that its first mentioned certificate can be used as default certificate
for only a subset of those frontends, we do not want the line to be
removable for some frontends and not the others. So if any of the ckch
instances corresponding to a crt-list line is a default instance, the
removal of the crt-list line will be forbidden.

It can be backported as far as 2.2.

reg-tests/ssl/del_ssl_crt-list.vtc

@@ -0,0 +1,104 @@
+#REGTEST_TYPE=devel
+
+# This reg-test uses the "del ssl crt-list" command to remove a line from a crt-list.
+
+# It performs three requests towards a frontend that uses simple.crt-list.
+# Between the second and third requests, a line is deleted from the crt-list,
+# which makes the third request fail since it would have used the deleted line
+# and the strict-sni option is enabled on the frontend.
+# Another test is performed as well. A line corresponding to the default instance
+# of a frontend that does not have the strict-sni option enabled cannot be deleted.
+
+varnishtest "Test the 'del ssl crt-list' feature of the CLI"
+#REQUIRE_VERSION=2.2
+#REQUIRE_OPTIONS=OPENSSL
+feature ignore_unknown_macro
+
+server s1 -repeat 2 {
+    rxreq
+    txresp
+} -start
+
+haproxy h1 -conf {
+    global
+        tune.ssl.default-dh-param 2048
+        tune.ssl.capture-cipherlist-size 1
+        crt-base ${testdir}
+        stats socket "${tmpdir}/h1/stats" level admin
+
+    defaults
+        mode http
+        option httplog
+        ${no-htx} option http-use-htx
+        log stderr local0 debug err
+        option logasap
+        timeout connect 100ms
+        timeout client  1s
+        timeout server  1s
+
+
+    listen clear-lst
+        bind "fd@${clearlst}"
+        balance roundrobin
+        http-response set-header X-SSL-Server-SHA1 %[ssl_s_sha1,hex]
+        server s1 "${tmpdir}/first-ssl.sock" ssl verify none sni str(record2.bug940.domain.tld)
+        server s2 "${tmpdir}/first-ssl.sock" ssl verify none sni str(record3.bug940.domain.tld)
+        server s3 "${tmpdir}/first-ssl.sock" ssl verify none sni str(record2.bug940.domain.tld)
+
+    listen first-ssl-fe
+        mode http
+        ${no-htx} option http-use-htx
+        bind "${tmpdir}/first-ssl.sock" ssl strict-sni crt-list ${testdir}/simple.crt-list
+        server s1 ${s1_addr}:${s1_port}
+
+    listen second-ssl-fe
+        mode http
+        ${no-htx} option http-use-htx
+        bind "${tmpdir}/second-ssl.sock" ssl crt-list ${testdir}/localhost.crt-list
+        server s1 ${s1_addr}:${s1_port}
+} -start
+
+client c1 -connect ${h1_clearlst_sock} {
+    txreq
+    rxresp
+    expect resp.http.X-SSL-Server-SHA1 == "2195C9F0FD58470313013FC27C1B9CF9864BD1C6"
+    expect resp.status == 200
+} -run
+
+client c1 -connect ${h1_clearlst_sock} {
+    txreq
+    rxresp
+    expect resp.http.X-SSL-Server-SHA1 == "A490D069DBAFBEE66DE434BEC34030ADE8BCCBF1"
+    expect resp.status == 200
+} -run
+
+haproxy h1 -cli {
+    send "del ssl crt-list ${testdir}/simple.crt-list ${testdir}/common.pem:2"
+    expect ~ "Entry '${testdir}/common.pem' deleted in crtlist '${testdir}/simple.crt-list'!"
+}
+
+haproxy h1 -cli {
+    send "show ssl crt-list -n ${testdir}/simple.crt-list"
+    expect !~ "common.pem:2"
+}
+
+# This connection should fail since the corresponding line was deleted from the crt-list
+# and the strict-sni option is enabled.
+client c1 -connect ${h1_clearlst_sock} {
+    txreq
+    rxresp
+    expect resp.status == 503
+} -run
+
+# We should not be able to delete the crt-list's first line since it is the
+# default certificate of this bind line and the strict-sni option is not enabled.
+haproxy h1 -cli {
+    send "del ssl crt-list ${testdir}/localhost.crt-list ${testdir}/common.pem:1"
+    expect ~ "Can't delete the entry: certificate '${testdir}/common.pem' cannot be deleted, it is used as default certificate by the following frontends:"
+}
+
+# We should be able to delete any line of the crt-list since the strict-sni option is enabled.
+haproxy h1 -cli {
+    send "del ssl crt-list ${testdir}/simple.crt-list ${testdir}/common.pem:1"
+    expect ~ "Entry '${testdir}/common.pem' deleted in crtlist '${testdir}/simple.crt-list'!"
+}

src/ssl_crtlist.c

@@ -1304,6 +1304,7 @@ static int cli_parse_del_crtlist(char **args, char *payload, struct appctx *appc
 	int linenum = 0;
 	char *colons;
 	char *end;
+	int error_message_dumped = 0;
 
 	if (!cli_has_level(appctx, ACCESS_LVL_ADMIN))
 		return 1;
@@ -1384,6 +1385,20 @@ static int cli_parse_del_crtlist(char **args, char *payload, struct appctx *appc
 		goto error;
 	}
 
+	/* Iterate over all the instances in order to see if any of them is a
+	 * default instance. If this is the case, the entry won't be suppressed. */
+	list_for_each_entry_safe(inst, inst_s, &entry->ckch_inst, by_crtlist_entry) {
+		if (inst->is_default && !inst->bind_conf->strict_sni) {
+			if (!error_message_dumped) {
+				memprintf(&err, "certificate '%s' cannot be deleted, it is used as default certificate by the following frontends:\n", cert_path);
+				error_message_dumped = 1;
+			}
+			memprintf(&err, "%s\t- %s:%d\n", err, inst->bind_conf->file, inst->bind_conf->line);
+		}
+	}
+	if (error_message_dumped)
+		goto error;
+
 	/* upon error free the ckch_inst and everything inside */
 
 	ebpt_delete(&entry->node);