libfdt: Fix bounds-checking bug in fdt_get_property()

The libfdt functions are supposed to behave tolerably well when practical,
even if given a corrupted device tree as input.  A silly mistake in
fdt_get_property() means we're bounds checking against the size of a pointer
instead of the size of a property header, meaning we can get bogus
behaviour in a corrupted device tree where the structure block ends in
what's supposed to be the middle of a property.

This patch corrects the problem (fdt_get_property() will now return
BADSTRUCTURE in this case), and also adds a testcase to catch the bug.

fdt_ro.c

@@ -193,7 +193,7 @@ struct fdt_property *fdt_get_property(const struct fdt_header *fdt,
 				/* Found it! */
 				int len = fdt32_to_cpu(prop->len);
 				prop = fdt_offset_ptr(fdt, offset,
-						      sizeof(prop)+len);
+						      sizeof(*prop)+len);
 				if (! prop)
 					return PTR_ERROR(FDT_ERR_BADSTRUCTURE);
 

tests/Makefile

@@ -6,7 +6,8 @@ LIB_TESTS = root_node find_property subnode_offset path_offset getprop \
 	sw_tree1 \
 	move_and_save \
 	open_pack rw_tree1 setprop del_property del_node
-TESTS = $(LIB_TESTS)
+LIBTREE_TESTS = truncated_property
+TESTS = $(LIB_TESTS) $(LIBTREE_TESTS)
 UTILS = dumptrees
 
 TREES = test_tree1.dtb
@@ -42,6 +43,8 @@ all:	$(TESTS) $(TREES)
 
 $(LIB_TESTS): %: testutils.o $(LIBFDT)
 
+$(LIBTREE_TESTS): %: testutils.o trees.o $(LIBFDT)
+
 dumptrees: %: trees.o
 
 $(TREES): dumptrees

tests/run_tests.sh

@@ -58,6 +58,9 @@ functional_tests () {
     run_test del_node test_tree1.dtb
     run_test rw_tree1
     tree1_tests rw_tree1.test.dtb
+
+    # Tests for behaviour on various sorts of corrupted trees
+    run_test truncated_property
 }
 
 stress_tests () {

tests/testdata.h

@@ -5,4 +5,5 @@
 
 #ifndef __ASSEMBLY__
 extern struct fdt_header _test_tree1;
+extern struct fdt_header _truncated_property;
 #endif /* ! __ASSEMBLY */

tests/trees.S

@@ -18,6 +18,7 @@
 	.byte	(val) & 0xff
 
 #define TREE_HDR(tree) \
+	.balign	4		; \
 	.globl	_##tree		; \
 _##tree:	\
 tree:	\
@@ -100,3 +101,16 @@ test_tree1_strings:
 	STRING(test_tree1, prop_int, "prop-int")
 	STRING(test_tree1, prop_str, "prop-str")
 test_tree1_end:
+
+	TREE_HDR(truncated_property)
+truncated_property_rsvmap:
+	RSVMAP_ENTRY(0, 0)
+
+truncated_property_struct:
+	BEGIN_NODE("")
+	PROPHDR(truncated_property, prop_truncated, 4)
+	/* Oops, no actual property data here */
+	
+truncated_property_strings:
+	STRING(truncated_property, prop_truncated, "truncated")
+truncated_property_end:

tests/truncated_property.c

@@ -0,0 +1,49 @@
+/*
+ * libfdt - Flat Device Tree manipulation
+ *	Testcase for misbehaviour on a truncated property
+ * Copyright (C) 2006 David Gibson, IBM Corporation.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public License
+ * as published by the Free Software Foundation; either version 2.1 of
+ * the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <fdt.h>
+#include <libfdt.h>
+
+#include "tests.h"
+#include "testdata.h"
+
+int main(int argc, char *argv[])
+{
+	void *fdt = &_truncated_property;
+	void *prop;
+	int err;
+	int len;
+
+	test_init(argc, argv);
+
+	prop = fdt_getprop(fdt, 0, "truncated", &len);
+	err = fdt_ptr_error(prop);
+	if (! err)
+		FAIL("fdt_getprop() succeeded on truncated property");
+	if (err != FDT_ERR_BADSTRUCTURE)
+		FAIL("fdt_getprop() failed with \"%s\" instead of \"%s\"",
+		     fdt_strerror(err), fdt_strerror(FDT_ERR_BADSTRUCTURE));
+
+	PASS();
+}