1 files changed, 33 insertions, 0 deletions
diff --git a/libbb/validate_filename.c b/libbb/validate_filename.c
new file mode 100644
index 0000000..2b9b80a
--- /dev/null
+++ b/libbb/validate_filename.c
@@ -0,0 +1,33 @@
+#include "libbb.h"
+
+int validate_filename(const char *path, const char *prefix)
+{
+	size_t path_len, prefix_len;
+
+	/* Check for the following properties:
+	 * 1) path start with prefix
+	 * 2) the next character after prefix is a '/'
+	 * 3) path does not contain '/../'
+	 * 4) path does not end in '/..'
+	 * return 0 if any of the properties does not hold
+	 * return 1 if all properties hold
+	 */
+	path_len= strlen(path);
+	prefix_len= strlen(prefix);
+	if (path_len < prefix_len)
+		return 0;
+
+	if (memcmp(path, prefix, prefix_len) != 0)
+		return 0;	/* property 1 */
+
+	if (path[prefix_len] != '/')
+		return 0;	/* property 2 */
+
+	if (strstr(path, "/../") != NULL)
+		return 0;	/* property 3 */
+
+	if (path_len >= 3 && strcmp(&path[path_len-3], "/..") == 0)
+		return 0;	/* property 4 */
+	
+	return 1;
+}