Fix find-credential following migrations

src/ctap2/credential_management.rs

@@ -447,14 +447,20 @@ where
     fn find_credential(&mut self, credential: &PublicKeyCredentialDescriptor) -> Option<PathBuf> {
         let credential_id_hash = self.hash(&credential.id[..]);
         let mut hex = [b'0'; 16];
-        super::format_hex(&credential_id_hash[..8], &mut hex);
+        let hex_str = super::format_hex(&credential_id_hash[..8], &mut hex);
         let dir = PathBuf::from(b"rk");
-        let filename = PathBuf::from(&hex);
 
-        syscall!(self
-            .trussed
-            .locate_file(Location::Internal, Some(dir), filename,))
-        .path
+        let mut maybe_entry =
+            try_syscall!(self.trussed.read_dir_first(Location::Internal, dir, None))
+                .ok()?
+                .entry;
+        while let Some(entry) = maybe_entry {
+            if entry.file_name().as_str().ends_with(&hex_str) {
+                return Some(entry.path().into());
+            }
+            maybe_entry = syscall!(self.trussed.read_dir_next()).entry;
+        }
+        None
     }
 
     pub fn delete_credential(

src/lib.rs

@@ -151,13 +151,16 @@ where
 }
 
 // EWW.. this is a bit unsafe isn't it
-fn format_hex(data: &[u8], mut buffer: &mut [u8]) {
+fn format_hex<'a>(data: &[u8], buffer: &'a mut [u8]) -> &'a str {
     const HEX_CHARS: &[u8] = b"0123456789abcdef";
-    for byte in data.iter() {
-        buffer[0] = HEX_CHARS[(byte >> 4) as usize];
-        buffer[1] = HEX_CHARS[(byte & 0xf) as usize];
-        buffer = &mut buffer[2..];
+    assert!(data.len() * 2 >= buffer.len());
+    for (idx, byte) in data.iter().enumerate() {
+        buffer[idx * 2] = HEX_CHARS[(byte >> 4) as usize];
+        buffer[idx * 2 + 1] = HEX_CHARS[(byte & 0xf) as usize];
     }
+
+    // SAFETY: we just added only ascii chars to buffer from 0 to data.len() - 1
+    unsafe { core::str::from_utf8_unchecked(&buffer[0..data.len() * 2]) }
 }
 
 // NB: to actually use this, replace the constant implementation with the inline assembly.
@@ -290,4 +293,14 @@ where
 }
 
 #[cfg(test)]
-mod test {}
+mod test {
+    use super::*;
+
+    #[test]
+    fn hex() {
+        let data = [0x01, 0x02, 0xB1, 0xA1];
+        let buffer = &mut [0; 8];
+        assert_eq!(format_hex(&data, buffer), "0102b1a1");
+        assert_eq!(buffer, b"0102b1a1");
+    }
+}