block: Parse filenames only when explicitly requested

When handling image filenames from legacy options such as -drive or from
tools, these filenames are parsed for protocol prefixes, including for
the json:{} pseudo-protocol.

This behaviour is intended for filenames that come directly from the
command line and for backing files, which may come from the image file
itself. Higher level management tools generally take care to verify that
untrusted images don't contain a bad (or any) backing file reference;
'qemu-img info' is a suitable tool for this.

However, for other files that can be referenced in images, such as
qcow2 data files or VMDK extents, the string from the image file is
usually not verified by management tools - and 'qemu-img info' wouldn't
be suitable because in contrast to backing files, it already opens these
other referenced files. So here the string should be interpreted as a
literal local filename. More complex configurations need to be specified
explicitly on the command line or in QMP.

This patch changes bdrv_open_inherit() so that it only parses filenames
if a new parameter parse_filename is true. It is set for the top level
in bdrv_open(), for the file child and for the backing file child. All
other callers pass false and disable filename parsing this way.

Cc: [email protected]
Signed-off-by: Kevin Wolf <[email protected]>
Reviewed-by: Eric Blake <[email protected]>
Reviewed-by: Stefan Hajnoczi <[email protected]>
Reviewed-by: Hanna Czenczek <[email protected]>

Author: kevmw

block.c

@@ -86,6 +86,7 @@ static BlockDriverState *bdrv_open_inherit(const char *filename,
                                            BlockDriverState *parent,
                                            const BdrvChildClass *child_class,
                                            BdrvChildRole child_role,
+                                           bool parse_filename,
                                            Error **errp);
 
 static bool bdrv_recurse_has_child(BlockDriverState *bs,
@@ -2055,7 +2056,8 @@ static void parse_json_protocol(QDict *options, const char **pfilename,
  * block driver has been specified explicitly.
  */
 static int bdrv_fill_options(QDict **options, const char *filename,
-                             int *flags, Error **errp)
+                             int *flags, bool allow_parse_filename,
+                             Error **errp)
 {
     const char *drvname;
     bool protocol = *flags & BDRV_O_PROTOCOL;
@@ -2097,7 +2099,7 @@ static int bdrv_fill_options(QDict **options, const char *filename,
     if (protocol && filename) {
         if (!qdict_haskey(*options, "filename")) {
             qdict_put_str(*options, "filename", filename);
-            parse_filename = true;
+            parse_filename = allow_parse_filename;
         } else {
             error_setg(errp, "Can't specify 'file' and 'filename' options at "
                              "the same time");
@@ -3660,7 +3662,8 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
     }
 
     backing_hd = bdrv_open_inherit(backing_filename, reference, options, 0, bs,
-                                   &child_of_bds, bdrv_backing_role(bs), errp);
+                                   &child_of_bds, bdrv_backing_role(bs), true,
+                                   errp);
     if (!backing_hd) {
         bs->open_flags |= BDRV_O_NO_BACKING;
         error_prepend(errp, "Could not open backing file: ");
@@ -3694,7 +3697,8 @@ int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
 static BlockDriverState *
 bdrv_open_child_bs(const char *filename, QDict *options, const char *bdref_key,
                    BlockDriverState *parent, const BdrvChildClass *child_class,
-                   BdrvChildRole child_role, bool allow_none, Error **errp)
+                   BdrvChildRole child_role, bool allow_none,
+                   bool parse_filename, Error **errp)
 {
     BlockDriverState *bs = NULL;
     QDict *image_options;
@@ -3725,7 +3729,8 @@ bdrv_open_child_bs(const char *filename, QDict *options, const char *bdref_key,
     }
 
     bs = bdrv_open_inherit(filename, reference, image_options, 0,
-                           parent, child_class, child_role, errp);
+                           parent, child_class, child_role, parse_filename,
+                           errp);
     if (!bs) {
         goto done;
     }
@@ -3735,6 +3740,33 @@ bdrv_open_child_bs(const char *filename, QDict *options, const char *bdref_key,
     return bs;
 }
 
+static BdrvChild *bdrv_open_child_common(const char *filename,
+                                         QDict *options, const char *bdref_key,
+                                         BlockDriverState *parent,
+                                         const BdrvChildClass *child_class,
+                                         BdrvChildRole child_role,
+                                         bool allow_none, bool parse_filename,
+                                         Error **errp)
+{
+    BlockDriverState *bs;
+    BdrvChild *child;
+
+    GLOBAL_STATE_CODE();
+
+    bs = bdrv_open_child_bs(filename, options, bdref_key, parent, child_class,
+                            child_role, allow_none, parse_filename, errp);
+    if (bs == NULL) {
+        return NULL;
+    }
+
+    bdrv_graph_wrlock();
+    child = bdrv_attach_child(parent, bs, bdref_key, child_class, child_role,
+                              errp);
+    bdrv_graph_wrunlock();
+
+    return child;
+}
+
 /*
  * Opens a disk image whose options are given as BlockdevRef in another block
  * device's options.
@@ -3758,27 +3790,15 @@ BdrvChild *bdrv_open_child(const char *filename,
                            BdrvChildRole child_role,
                            bool allow_none, Error **errp)
 {
-    BlockDriverState *bs;
-    BdrvChild *child;
-
-    GLOBAL_STATE_CODE();
-
-    bs = bdrv_open_child_bs(filename, options, bdref_key, parent, child_class,
-                            child_role, allow_none, errp);
-    if (bs == NULL) {
-        return NULL;
-    }
-
-    bdrv_graph_wrlock();
-    child = bdrv_attach_child(parent, bs, bdref_key, child_class, child_role,
-                              errp);
-    bdrv_graph_wrunlock();
-
-    return child;
+    return bdrv_open_child_common(filename, options, bdref_key, parent,
+                                  child_class, child_role, allow_none, false,
+                                  errp);
 }
 
 /*
- * Wrapper on bdrv_open_child() for most popular case: open primary child of bs.
+ * This does mostly the same as bdrv_open_child(), but for opening the primary
+ * child of a node. A notable difference from bdrv_open_child() is that it
+ * enables filename parsing for protocol names (including json:).
  *
  * @parent can move to a different AioContext in this function.
  */
@@ -3793,8 +3813,8 @@ int bdrv_open_file_child(const char *filename,
     role = parent->drv->is_filter ?
         (BDRV_CHILD_FILTERED | BDRV_CHILD_PRIMARY) : BDRV_CHILD_IMAGE;
 
-    if (!bdrv_open_child(filename, options, bdref_key, parent,
-                         &child_of_bds, role, false, errp))
+    if (!bdrv_open_child_common(filename, options, bdref_key, parent,
+                                &child_of_bds, role, false, true, errp))
     {
         return -EINVAL;
     }
@@ -3839,7 +3859,8 @@ BlockDriverState *bdrv_open_blockdev_ref(BlockdevRef *ref, Error **errp)
 
     }
 
-    bs = bdrv_open_inherit(NULL, reference, qdict, 0, NULL, NULL, 0, errp);
+    bs = bdrv_open_inherit(NULL, reference, qdict, 0, NULL, NULL, 0, false,
+                           errp);
     obj = NULL;
     qobject_unref(obj);
     visit_free(v);
@@ -3929,7 +3950,7 @@ static BlockDriverState * no_coroutine_fn
 bdrv_open_inherit(const char *filename, const char *reference, QDict *options,
                   int flags, BlockDriverState *parent,
                   const BdrvChildClass *child_class, BdrvChildRole child_role,
-                  Error **errp)
+                  bool parse_filename, Error **errp)
 {
     int ret;
     BlockBackend *file = NULL;
@@ -3977,9 +3998,11 @@ bdrv_open_inherit(const char *filename, const char *reference, QDict *options,
     }
 
     /* json: syntax counts as explicit options, as if in the QDict */
-    parse_json_protocol(options, &filename, &local_err);
-    if (local_err) {
-        goto fail;
+    if (parse_filename) {
+        parse_json_protocol(options, &filename, &local_err);
+        if (local_err) {
+            goto fail;
+        }
     }
 
     bs->explicit_options = qdict_clone_shallow(options);
@@ -4004,7 +4027,8 @@ bdrv_open_inherit(const char *filename, const char *reference, QDict *options,
                                      parent->open_flags, parent->options);
     }
 
-    ret = bdrv_fill_options(&options, filename, &flags, &local_err);
+    ret = bdrv_fill_options(&options, filename, &flags, parse_filename,
+                            &local_err);
     if (ret < 0) {
         goto fail;
     }
@@ -4073,7 +4097,7 @@ bdrv_open_inherit(const char *filename, const char *reference, QDict *options,
 
         file_bs = bdrv_open_child_bs(filename, options, "file", bs,
                                      &child_of_bds, BDRV_CHILD_IMAGE,
-                                     true, &local_err);
+                                     true, true, &local_err);
         if (local_err) {
             goto fail;
         }
@@ -4222,7 +4246,7 @@ BlockDriverState *bdrv_open(const char *filename, const char *reference,
     GLOBAL_STATE_CODE();
 
     return bdrv_open_inherit(filename, reference, options, flags, NULL,
-                             NULL, 0, errp);
+                             NULL, 0, true, errp);
 }
 
 /* Return true if the NULL-terminated @list contains @str */