String operations could silently truncate long strings, leaving the output

corrupted.  Mark's patch fixes this be removing the MAXTOK limitation on
substring operations and allowing the putback buffer size to be the limiting
factor.  If the putback buffer size if reached, m4 gives an error instead of
silently truncating the string.

PR:		bin/26619
Submitted by:	Mark Peek <mark-ml@whistle.com>
MFC after:	5 days

1 files changed, 8 insertions, 8 deletions

diff --git a/usr.bin/m4/eval.c b/usr.bin/m4/eval.c
index e424815..d2ac3c8 100644
--- a/usr.bin/m4/eval.c
+++ b/usr.bin/m4/eval.c
@@ -717,22 +717,22 @@ register int argc;
 	register unsigned char *ap, *fc, *k;
 	register int nc;
 
+	ap = argv[2];		       /* target string */
+#ifdef EXPR
+	fc = ap + expr(argv[3]);       /* first char */
+#else
+	fc = ap + atoi(argv[3]);       /* first char */
+#endif
 	if (argc < 5)
-		nc = MAXTOK;
+		nc = strlen(fc);
 	else
 #ifdef EXPR
 		nc = expr(argv[4]);
 #else
 		nc = atoi(argv[4]);
 #endif
-	ap = argv[2];		       /* target string */
-#ifdef EXPR
-	fc = ap + expr(argv[3]);       /* first char */
-#else
-	fc = ap + atoi(argv[3]);       /* first char */
-#endif
 	if (fc >= ap && fc < ap + strlen(ap))
-		for (k = fc + min(nc, strlen(fc)) - 1; k >= fc; k--)
+		for (k = fc + nc - 1; k >= fc; k--)
 			putback(*k);
 }