Merge commit from fork

unzip: reject absolute or traversing symlink targets
(cherry picked from commit 9bd1a06adb)

unzip/bsdunzip.c

@@ -738,6 +738,14 @@ recheck:
 		error("close('%s')", *path);
 }
 
+static int
+pathname_is_insecure(const char* pathname)
+{
+	return (pathname[0] == '/' ||
+	    strncmp(pathname, "../", 3) == 0 ||
+	    strstr(pathname, "/../") != NULL);
+}
+
 /*
  * Extract a zipfile entry: first perform some sanity checks to ensure
  * that it is either a directory or a regular file and that the path is
@@ -757,6 +765,7 @@ static void
 extract(struct archive *a, struct archive_entry *e)
 {
 	char *pathname, *realpathname;
+	const char *linktarget;
 	mode_t filetype;
 	char *p, *q;
 
@@ -768,15 +777,22 @@ extract(struct archive *a, struct archive_entry *e)
 	filetype = archive_entry_filetype(e);
 
 	/* sanity checks */
-	if (pathname[0] == '/' ||
-	    strncmp(pathname, "../", 3) == 0 ||
-	    strstr(pathname, "/../") != NULL) {
+	if (pathname_is_insecure(pathname)) {
 		warningx("skipping insecure entry '%s'", pathname);
 		ac(archive_read_data_skip(a));
 		free(pathname);
 		return;
 	}
 
+	if (S_ISLNK(filetype) &&
+	    ((linktarget = archive_entry_symlink(e)) != NULL) &&
+	    pathname_is_insecure(linktarget)) {
+		warningx("skipping insecure symlink '%s' to '%s'", pathname, linktarget);
+		ac(archive_read_data_skip(a));
+		free(pathname);
+		return;
+	}
+
 	/* I don't think this can happen in a zipfile.. */
 	if (!S_ISDIR(filetype) && !S_ISREG(filetype) && !S_ISLNK(filetype)) {
 		warningx("skipping non-regular entry '%s'", pathname);