Some netgraph parse types (such as for the 'value' field in ng_ksocket's

'struct ng_ksocket_sockopt') like to peek into the ng_mesg header for
information. Make sure when generating default values that we provide
a valid header to peek into.

MFC after:	1 week

1 files changed, 15 insertions, 8 deletions

diff --git a/sys/netgraph/ng_parse.c b/sys/netgraph/ng_parse.c
index a69cfa6..660cbd3 100644
--- a/sys/netgraph/ng_parse.c
+++ b/sys/netgraph/ng_parse.c
@@ -1307,6 +1307,8 @@ static int
 ng_unparse_composite(const struct ng_parse_type *type, const u_char *data,
 	int *off, char *cbuf, int cbuflen, const enum comptype ctype)
 {
+	const struct ng_mesg *const hdr
+	    = (const struct ng_mesg *)(data - sizeof(*hdr));
 	const int num = ng_get_composite_len(type, data, data + *off, ctype);
 	const int workSize = 20 * 1024;		/* XXX hard coded constant */
 	int nextIndex = 0, didOne = 0;
@@ -1329,14 +1331,19 @@ ng_unparse_composite(const struct ng_parse_type *type, const u_char *data,
 		/* Skip any alignment pad bytes */
 		*off += ng_parse_get_elem_pad(type, index, ctype, *off);
 
-		/* See if element is equal to its default value; skip if so */
-		if (*off < workSize) {
-			int tempsize = workSize - *off;
-
-			bcopy(data, workBuf, *off);
-			if (ng_get_composite_elem_default(type, index, workBuf,
-			      workBuf + *off, &tempsize, ctype) == 0
-			    && bcmp(workBuf + *off,
+		/*
+		 * See if element is equal to its default value; skip if so.
+		 * Copy struct ng_mesg header for types that peek into it.
+		 */
+		if (sizeof(*hdr) + *off < workSize) {
+			int tempsize = workSize - sizeof(*hdr) - *off;
+
+			bcopy(hdr, workBuf, sizeof(*hdr));
+			bcopy(data + sizeof(*hdr), workBuf, *off);
+			if (ng_get_composite_elem_default(type, index, workBuf
+			      + sizeof(*hdr), workBuf + sizeof(*hdr) + *off,
+			      &tempsize, ctype) == 0
+			    && bcmp(workBuf + sizeof(*hdr) + *off,
 			      data + *off, tempsize) == 0) {
 				*off += tempsize;
 				continue;