qemu-char: convert to use error checked base64 decode

Switch from using g_base64_decode over to qbase64_decode
in order to get error checking of the base64 input data.
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>

qapi-schema.json

@@ -295,8 +295,6 @@
 # @format: #optional data encoding (default 'utf8').
 #          - base64: data must be base64 encoded text.  Its binary
 #            decoding gets written.
-#            Bug: invalid base64 is currently not rejected.
-#            Whitespace *is* invalid.
 #          - utf8: data's UTF-8 encoding is written
 #          - data itself is always Unicode regardless of format, like
 #            any other string.

qemu-char.c

@@ -32,6 +32,7 @@
 #include "qapi/qmp-input-visitor.h"
 #include "qapi/qmp-output-visitor.h"
 #include "qapi-visit.h"
+#include "qemu/base64.h"
 
 #include <unistd.h>
 #include <fcntl.h>
@@ -3264,7 +3265,12 @@ void qmp_ringbuf_write(const char *device, const char *data,
     }
 
     if (has_format && (format == DATA_FORMAT_BASE64)) {
-        write_data = g_base64_decode(data, &write_count);
+        write_data = qbase64_decode(data, -1,
+                                    &write_count,
+                                    errp);
+        if (!write_data) {
+            return;
+        }
     } else {
         write_data = (uint8_t *)data;
         write_count = strlen(data);

qmp-commands.hx

@@ -512,8 +512,6 @@ Arguments:
 - "data": data to write (json-string)
 - "format": data format (json-string, optional)
           - Possible values: "utf8" (default), "base64"
-            Bug: invalid base64 is currently not rejected.
-            Whitespace *is* invalid.
 
 Example: