Allow negative seek offsets for files that can be seeked upon. It

makes dd(1) a more complete "filter", even if this functionality is
limited to seekable streams.

2 files changed, 10 insertions, 2 deletions

diff --git a/bin/dd/args.c b/bin/dd/args.c
index e118712..252f0fa 100644
--- a/bin/dd/args.c
+++ b/bin/dd/args.c
@@ -428,7 +428,7 @@ get_offset(val)
 	quad_t num;
 
 	num = get_num(val);
-	if (num > QUAD_MAX || num < 0)		/* XXX quad_t != off_t */
-		errx(1, "%s: illegal offset", oper);	/* Too big/negative. */
+	if (num > QUAD_MAX)	/* XXX can't happen && quad_t != off_t */
+		errx(1, "%s: illegal offset", oper);	/* Too big. */
 	return ((off_t)num);
 }
diff --git a/bin/dd/position.c b/bin/dd/position.c
index 10020d0..1a9c4b1 100644
--- a/bin/dd/position.c
+++ b/bin/dd/position.c
@@ -76,6 +76,10 @@ pos_in()
 		return;
 	}
 
+	/* Don't try to read a really weird amount (like negative). */
+	if (in.offset < 0)
+		errx(1, "%s: illegal offset", "iseek/skip");
+
 	/*
 	 * Read the data.  If a pipe, read until satisfy the number of bytes
 	 * being skipped.  No differentiation for reading complete and partial
@@ -138,6 +142,10 @@ pos_out()
 		return;
 	}
 
+	/* Don't try to read a really weird amount (like negative). */
+	if (out.offset < 0)
+		errx(1, "%s: illegal offset", "oseek/seek");
+
 	/* If no read access, try using mtio. */
 	if (out.flags & NOREAD) {
 		t_op.mt_op = MTFSR;