Check for null bytes in filenames in 'expand-file-name' (bug#49723)

* src/fileio.c (expand-file-name): Check for null bytes for both
NAME and DEFAULT-DIRECTORY arguments.  Also check for null bytes
in buffer-local default-directory, assuming it is used.
* src/coding.c (encode_file_name): Use CHECK_STRING_NULL_BYTES.
* src/lisp.h (CHECK_STRING_NULL_BYTES): Add function for checking
for null bytes in Lisp strings.
* test/src/fileio-tests.el (fileio-test--expand-file-name-null-bytes):
Add test for new changes to expand-file-name.
* etc/NEWS: Announce changes.

1 files changed, 7 insertions, 0 deletions

diff --git a/src/lisp.h b/src/lisp.h
index 7bfc69b647b..9716b34baee 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -1615,6 +1615,13 @@ STRING_SET_CHARS (Lisp_Object string, ptrdiff_t newsize)
   XSTRING (string)->u.s.size = newsize;
 }
 
+INLINE void
+CHECK_STRING_NULL_BYTES (Lisp_Object string)
+{
+  CHECK_TYPE (memchr (SSDATA (string), '\0', SBYTES (string)) == NULL,
+              Qfilenamep, string);
+}
+
 /* A regular vector is just a header plus an array of Lisp_Objects.  */
 
 struct Lisp_Vector