virnetdevopenvswitch: Try to unescape ovs-vsctl reply in one specific case

During testing of my patch v6.10.0-rc1~221 it was found that

  'ovs-vsctl get Interface $name name' or
  'ovs-vsctl find Interface options:vhost-server-path=$path'

may return a string in double quotes, e.g. "vhost-user1". Later
investigation of openvswitch code showed, that early versions
(like 1.3.0) have somewhat restrictive set of safe characters
(isalpha() || '_' || '-' || '.'), which is then refined with
increasing version. For instance, version 2.11.4 has: isalnum()
|| '_' || '-' || '.'. If the string that ovs-vsctl wants to
output contains any other character it is escaped. You want to be
looking at ovsdb_atom_to_string() which handles outputting of a
single string and calls string_needs_quotes() and possibly
json_serialize_string() in openvswitch code base.

Since the interfaces are usually named "vhost-userN" we are
facing a problem where with one version we get the name in double
quotes and with another we get plain name without funny business.

Because of json involved I thought, let's make ovs-vsctl output
into JSON format and then use our JSON parser, but guess what -
ovs-vsctl ignores --format=json. But with a little help of
g_strdup_printf() it can be turned into JSON.

Fixes: e4c29e2904197472919d050c67acfd59f0144bbc
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1767013
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Laine Stump <laine@redhat.com>

src/libvirt_private.syms

@@ -2676,6 +2676,7 @@ virNetDevOpenvswitchGetVhostuserIfname;
 virNetDevOpenvswitchInterfaceGetMaster;
 virNetDevOpenvswitchInterfaceParseStats;
 virNetDevOpenvswitchInterfaceStats;
+virNetDevOpenvswitchMaybeUnescapeReply;
 virNetDevOpenvswitchRemovePort;
 virNetDevOpenvswitchSetMigrateData;
 virNetDevOpenvswitchSetTimeout;

src/util/virnetdevopenvswitch.c

@@ -460,6 +460,48 @@ virNetDevOpenvswitchInterfaceGetMaster(const char *ifname, char **master)
 }
 
 
+/**
+ * virNetDevOpenvswitchMaybeUnescapeReply:
+ * @reply: a string to unescape
+ *
+ * Depending on ovs-vsctl version a string might be escaped. For instance:
+ *  -version 2.11.4 allows only is_alpha(), an underscore, a dash or a dot,
+ *  -version 2.14.0 allows only is_alnum(), an underscore, a dash or a dot,
+ * any other character causes the string to be escaped.
+ *
+ * What this function does, is it checks whether @reply string consists solely
+ * from safe, not escaped characters (as defined by version 2.14.0) and if not
+ * an error is reported. If @reply is a string enclosed in double quotes, but
+ * otherwise safe those double quotes are removed.
+ *
+ * Returns: 0 on success,
+ *         -1 otherwise (with error reported).
+ */
+int
+virNetDevOpenvswitchMaybeUnescapeReply(char *reply)
+{
+    g_autoptr(virJSONValue) json = NULL;
+    g_autofree char *jsonStr = NULL;
+    const char *tmp = NULL;
+    size_t replyLen = strlen(reply);
+
+    if (*reply != '"')
+        return 0;
+
+    jsonStr = g_strdup_printf("{\"name\": %s}", reply);
+    if (!(json = virJSONValueFromString(jsonStr)))
+        return -1;
+
+    if (!(tmp = virJSONValueObjectGetString(json, "name"))) {
+        virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
+                       _("Malformed ovs-vsctl output"));
+        return -1;
+    }
+
+    return virStrcpy(reply, tmp, replyLen);
+}
+
+
 /**
  * virNetDevOpenvswitchGetVhostuserIfname:
  * @path: the path of the unix socket
@@ -522,6 +564,11 @@ virNetDevOpenvswitchGetVhostuserIfname(const char *path,
         return 0;
     }
 
+    if (virNetDevOpenvswitchMaybeUnescapeReply(*ifname) < 0) {
+        VIR_FREE(*ifname);
+        return -1;
+    }
+
     return 1;
 }
 

src/util/virnetdevopenvswitch.h

@@ -60,6 +60,10 @@ int virNetDevOpenvswitchInterfaceStats(const char *ifname,
 int virNetDevOpenvswitchInterfaceGetMaster(const char *ifname, char **master)
     ATTRIBUTE_NONNULL(1) G_GNUC_WARN_UNUSED_RESULT;
 
+int
+virNetDevOpenvswitchMaybeUnescapeReply(char *reply)
+    ATTRIBUTE_NONNULL(1) G_GNUC_WARN_UNUSED_RESULT;
+
 int virNetDevOpenvswitchGetVhostuserIfname(const char *path,
                                            bool server,
                                            char **ifname)

tests/virnetdevopenvswitchtest.c

@@ -75,6 +75,42 @@ testInterfaceParseStats(const void *opaque)
 }
 
 
+typedef struct _escapeData escapeData;
+struct _escapeData {
+    const char *input;
+    const char *expect;
+};
+
+
+static int
+testNameEscape(const void *opaque)
+{
+    const escapeData *data = opaque;
+    g_autofree char *reply = g_strdup(data->input);
+    int rv;
+
+    rv = virNetDevOpenvswitchMaybeUnescapeReply(reply);
+
+    if (data->expect) {
+        if (rv < 0 || STRNEQ(reply, data->expect)) {
+            fprintf(stderr,
+                    "Unexpected failure, expected: %s for input %s got %s\n",
+                    data->expect, data->input, reply);
+            return -1;
+        }
+    } else {
+        if (rv >= 0) {
+            fprintf(stderr,
+                    "Unexpected success, input %s got %s\n",
+                    data->input, reply);
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+
 static int
 mymain(void)
 {
@@ -94,6 +130,22 @@ mymain(void)
     TEST_INTERFACE_STATS("stats1.json", 9, 12, 11, 10, 2, 8, 5, 4);
     TEST_INTERFACE_STATS("stats2.json", 12406, 173, 0, 0, 0, 0, 0, 0);
 
+#define TEST_NAME_ESCAPE(str, fail) \
+    do { \
+        const escapeData data = {str, fail};\
+        if (virTestRun("Name escape " str, testNameEscape, &data) < 0) \
+            ret = -1; \
+    } while (0)
+
+    TEST_NAME_ESCAPE("", "");
+    TEST_NAME_ESCAPE("\"\"", "");
+    TEST_NAME_ESCAPE("vhost-user1", "vhost-user1");
+    TEST_NAME_ESCAPE("\"vhost-user1\"", "vhost-user1");
+    TEST_NAME_ESCAPE("\"vhost_user-name.to.escape1", NULL);
+    TEST_NAME_ESCAPE("\"vhost_user-name.to\\\"escape1\"", "vhost_user-name.to\"escape1");
+    TEST_NAME_ESCAPE("\"vhost\"user1\"", NULL);
+    TEST_NAME_ESCAPE("\"\\\\", NULL);
+
     return ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
 }