Regenerate temporary passwords with null bytes

Previously, we silently cut off temporary passwords that contained a
null byte.  With the change to CString, we returned a LibraryError
instead.  With this patch, we change to generate_password function to
continue generating passwords until we have a password without a null
byte.

The chance of generating a password with a null byte is ca. 10 % for our
temporary password with 25 characters.  Therefore the chance of having
to re-generate the password multiple times is low enough that we don’t
bother with re-generating only the null bytes of the password for the
time being.  This should be improved in the future.

1 files changed, 9 insertions, 3 deletions

diff --git a/src/util.rs b/src/util.rs
index b9b1a68..a0d0d1b 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -76,9 +76,15 @@ pub fn get_last_error() -> Error {
 }
 
 pub fn generate_password(length: usize) -> Result<CString, Error> {
-    let mut data = vec![0u8; length];
-    OsRng.fill_bytes(&mut data[..]);
-    get_cstring(data)
+    loop {
+        // Randomly generate a password until we get a string *without* null bytes.  Otherwise
+        // the string would be cut off prematurely due to null-termination in C.
+        let mut data = vec![0u8; length];
+        OsRng.fill_bytes(&mut data[..]);
+        if let Ok(s) = CString::new(data) {
+            return Ok(s);
+        }
+    }
 }
 
 pub fn get_cstring<T: Into<Vec<u8>>>(s: T) -> Result<CString, Error> {