diff -up libarchive-2.8.4/libarchive/archive_write.c.bak libarchive-2.8.4/libarchive/archive_write.c
--- libarchive-2.8.4/libarchive/archive_write.c.bak	2010-03-07 19:07:40.000000000 +0100
+++ libarchive-2.8.4/libarchive/archive_write.c	2013-03-28 16:47:06.000000000 +0100
@@ -459,8 +459,13 @@ static ssize_t
 _archive_write_data(struct archive *_a, const void *buff, size_t s)
 {
 	struct archive_write *a = (struct archive_write *)_a;
+	const size_t max_write = INT_MAX;
+
 	__archive_check_magic(&a->archive, ARCHIVE_WRITE_MAGIC,
 	    ARCHIVE_STATE_DATA, "archive_write_data");
+	/* In particular, this catches attempts to pass negative values. */
+	if (s > max_write)
+		s = max_write;
 	archive_clear_error(&a->archive);
 	return ((a->format_write_data)(a, buff, s));
 }