libfdt: Fix bugs in fdt_get_path()

The current implementation of fdt_get_path() has a couple of bugs, fixed by this patch.

First, contrary to its documentation, on success it returns the length of the node's path, rather than 0. The testcase is correspondingly wrong, and the patch fixes this as well.

Second, in some circumstances, it will return -FDT_ERR_BADOFFSET instead of -FDT_ERR_NOSPACE when given insufficient buffer space. Specifically this happens when there is insufficient space even to hold the path's second last component. This behaviour is corrected, and the testcase updated to check it.

Signed-off-by David Gibson <[email protected]>

Index: dtc/tests/get_path.c
===================================================================

tests/get_path.c +7 -3

@@ -43,6 +43,8 @@ static void check_path_buf(void *fdt, co
 	memset(buf, POISON, sizeof(buf)); /* poison the buffer */
 
 	len = fdt_get_path(fdt, offset, buf, buflen);
+	verbose_printf("get_path() %s -> %d -> %s\n", path, offset, buf);
+
 	if (buflen <= pathlen) {
 		if (len != -FDT_ERR_NOSPACE)
 			FAIL("fdt_get_path([%d bytes]) returns %d with "

@@ -51,9 +53,9 @@ static void check_path_buf(void *fdt, co
 		if (len < 0)
 			FAIL("fdt_get_path([%d bytes]): %s", buflen,
 			     fdt_strerror(len));
-		if (len != pathlen)
-			FAIL("fdt_get_path([%d bytes]) reports length %d "
-			     "instead of %d", buflen, len, pathlen);
+		if (len != 0)
+			FAIL("fdt_get_path([%d bytes]) returns %d "
+			     "instead of 0", buflen, len);
 		if (strcmp(buf, path) != 0)
 			FAIL("fdt_get_path([%d bytes]) returns \"%s\" "
 			     "instead of \"%s\"", buflen, buf, path);

@@ -70,6 +72,8 @@ static void check_path(void *fdt, const 
 	check_path_buf(fdt, path, pathlen, 1024);
 	check_path_buf(fdt, path, pathlen, pathlen+1);
 	check_path_buf(fdt, path, pathlen, pathlen);
+	check_path_buf(fdt, path, pathlen, 0);
+	check_path_buf(fdt, path, pathlen, 2);
 }
 
 int main(int argc, char *argv[])

Index: dtc/libfdt/fdt_ro.c
===================================================================

libfdt/fdt_ro.c +11 -12

@@ -328,9 +328,6 @@ int fdt_get_path(const void *fdt, int no
 	for (offset = 0, depth = 0;
 	     (offset >= 0) && (offset <= nodeoffset);
 	     offset = fdt_next_node(fdt, offset, &depth)) {
-		if (pdepth < depth)
-			continue; /* overflowed buffer */
-
 		while (pdepth > depth) {
 			do {
 				p--;

@@ -338,14 +335,16 @@ int fdt_get_path(const void *fdt, int no
 			pdepth--;
 		}
 
-		name = fdt_get_name(fdt, offset, &namelen);
-		if (!name)
-			return namelen;
-		if ((p + namelen + 1) <= buflen) {
-			memcpy(buf + p, name, namelen);
-			p += namelen;
-			buf[p++] = '/';
-			pdepth++;
+		if (pdepth >= depth) {
+			name = fdt_get_name(fdt, offset, &namelen);
+			if (!name)
+				return namelen;
+			if ((p + namelen + 1) <= buflen) {
+				memcpy(buf + p, name, namelen);
+				p += namelen;
+				buf[p++] = '/';
+				pdepth++;
+			}
 		}
 
 		if (offset == nodeoffset) {

@@ -355,7 +354,7 @@ int fdt_get_path(const void *fdt, int no
 			if (p > 1) /* special case so that root path is "/", not "" */
 				p--;
 			buf[p] = '\0';
-			return p;
+			return 0;
 		}
 	}
 

FYI, I propose to pick this up for the *NEXT* release of u-boot ("Yellow Submarine" ;-). My reasoning is that (1) the current window closes today, which makes me uncomfortable WRT putting in changes today and (2) this appears to be a latent bug (at worst, a misleading error message); I have not seen evidence that it is causing problems at the moment.

The current implementation of fdt_get_path() has a couple of bugs, fixed by this patch.

First, contrary to its documentation, on success it returns the length of the node's path, rather than 0. The testcase is correspondingly wrong, and the patch fixes this as well.

Second, in some circumstances, it will return -FDT_ERR_BADOFFSET instead of -FDT_ERR_NOSPACE when given insufficient buffer space. Specifically this happens when there is insufficient space even to hold the path's second last component. This behaviour is corrected, and the testcase updated to check it.

Signed-off-by David Gibson <[email protected]>