Handle integer overflow in check_property_phandle_args()

If the corresponding '#xxx-cells' value is much too large, an integer
overflow can prevent the checks in check_property_phandle_args() from
correctly determining that the checked property is too short for the
given cells value.  This leads to an infinite loops.

This patch fixes the bug, and adds a testcase for it.  Further
information in https://github.com/dgibson/dtc/issues/64

Reported-by: Anciety <anciety@pku.edu.cn>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

checks.c

@@ -1382,10 +1382,10 @@ struct provider {
 };
 
 static void check_property_phandle_args(struct check *c,
-					  struct dt_info *dti,
-				          struct node *node,
-				          struct property *prop,
-				          const struct provider *provider)
+					struct dt_info *dti,
+					struct node *node,
+					struct property *prop,
+					const struct provider *provider)
 {
 	struct node *root = dti->dt;
 	unsigned int cell, cellsize = 0;
@@ -1401,6 +1401,7 @@ static void check_property_phandle_args(struct check *c,
 		struct node *provider_node;
 		struct property *cellprop;
 		cell_t phandle;
+		unsigned int expected;
 
 		phandle = propval_cell_n(prop, cell);
 		/*
@@ -1450,10 +1451,12 @@ static void check_property_phandle_args(struct check *c,
 			break;
 		}
 
-		if (prop->val.len < ((cell + cellsize + 1) * sizeof(cell_t))) {
+		expected = (cell + cellsize + 1) * sizeof(cell_t);
+		if ((expected <= cell) || prop->val.len < expected) {
 			FAIL_PROP(c, dti, node, prop,
-				  "property size (%d) too small for cell size %d",
+				  "property size (%d) too small for cell size %u",
 				  prop->val.len, cellsize);
+			break;
 		}
 	}
 }

tests/phandle-args-overflow.dts

@@ -0,0 +1,18 @@
+/dts-v1/;
+
+/*
+ * https://github.com/dgibson/dtc/issues/64
+ *
+ * Certain dtc versions had a bug where this input caused an infinite
+ * loop in check_property_phandle_args().
+ *
+ */
+
+/ {
+    clocks = <&ref &ref>;
+
+    ref: poc {
+        phandle = <1>;
+        #clock-cells = <0xffffffff>;
+    };
+};

tests/run_tests.sh

@@ -513,6 +513,9 @@ libfdt_tests () {
     run_dtc_test -I fs -O dtb -o fs.test_tree1.test.dtb $FSBASE/test_tree1
     run_test dtbs_equal_unordered -m fs.test_tree1.test.dtb test_tree1.dtb
 
+    ## https://github.com/dgibson/dtc/issues/64
+    check_tests "$SRCDIR/phandle-args-overflow.dts" clocks_property
+
     # check full tests
     for good in test_tree1.dtb; do
 	run_test check_full $good