mnt: Don't validate mounts on pre-dump

This is for two reasons. First, validation can meet external mount
and will call plugins, which is not correct on pre-dump and actually
crashes on uninitilized plugins lists. Second, even if on pre-dump
mount tree is not "supported" this can be a temporary situation (yes,
yes, unlikely, but still).

On the other hand, it's better to fail earlier, but that's another
story.
Reported-by: Sowmini Varadhan <sowmini.varadhan@oracle.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Acked-by: Andrew Vagin <avagin@parallels.com>

include/namespaces.h

@@ -48,7 +48,7 @@ extern struct collect_image_info nsfile_cinfo;
 
 extern int walk_namespaces(struct ns_desc *nd, int (*cb)(struct ns_id *, void *), void *oarg);
 extern int collect_namespaces(bool for_dump);
-extern int collect_mnt_namespaces(void);
+extern int collect_mnt_namespaces(bool for_dump);
 extern int dump_mnt_namespaces(void);
 extern int dump_namespaces(struct pstree_item *item, unsigned int ns_flags);
 extern int prepare_namespace(struct pstree_item *item, unsigned long clone_flags);

mount.c

@@ -2146,7 +2146,7 @@ static int collect_mntns(struct ns_id *ns, void *oarg)
 	return 0;
 }
 
-int collect_mnt_namespaces(void)
+int collect_mnt_namespaces(bool for_dump)
 {
 	int need_to_validate = 0, ret;
 
@@ -2154,7 +2154,7 @@ int collect_mnt_namespaces(void)
 	if (ret)
 		goto err;
 
-	if (need_to_validate) {
+	if (for_dump && need_to_validate) {
 		if (collect_shared(mntinfo))
 			goto err;
 		if (validate_mounts(mntinfo, true))

namespaces.c

@@ -573,7 +573,7 @@ int collect_namespaces(bool for_dump)
 {
 	int ret;
 
-	ret = collect_mnt_namespaces();
+	ret = collect_mnt_namespaces(for_dump);
 	if (ret < 0)
 		return ret;