security: harden WebDAV server against Slowloris/connection starvation and fix LZ4 bomb protection

src/crypto.rs

@@ -436,7 +436,19 @@ pub fn decrypt_chunk(
         match buffer[0] {
             COMPRESSION_NONE => Ok(buffer[1..].to_vec()),
             COMPRESSION_LZ4 => {
-                let decompressed = lz4_flex::decompress_size_prepended(&buffer[1..])
+                let payload = &buffer[1..];
+                if payload.len() < 4 {
+                    bail!("LZ4-Chunk beschädigt: Payload zu kurz für Längen-Präfix");
+                }
+                let uncompressed_size = u32::from_le_bytes(payload[0..4].try_into().unwrap()) as usize;
+                if uncompressed_size > CHUNK_SIZE {
+                    bail!(
+                        "LZ4-Dekomprimierungsfehler: Decompression-Bomb Schutz ausgelöst (angeforderte Größe {} Bytes > Limit {} Bytes)",
+                        uncompressed_size,
+                        CHUNK_SIZE
+                    );
+                }
+                let decompressed = lz4_flex::decompress_size_prepended(payload)
                     .map_err(|e| anyhow::anyhow!("LZ4-Dekomprimierungsfehler im Chunk: {e}"))?;
                 Ok(decompressed)
             }
@@ -704,6 +716,37 @@ mod tests {
         let recovered_cid_1 = i64::from_le_bytes(unwrapped_1[64..72].try_into().unwrap());
         assert_eq!(recovered_cid_1, carrier_node_id);
     }
+
+    #[test]
+    fn test_lz4_decompression_bomb_protection() {
+        use aes_gcm::KeyInit;
+        let dek = generate_dek();
+        let cipher = Aes256Gcm::new_from_slice(&*dek).unwrap();
+        let node_id = 999;
+        let chunk_index = 0;
+        let aad = build_chunk_aad(node_id, chunk_index);
+
+        // Erstelle präparierte LZ4-Payload mit deklarierter Größe von 5 MB (> 1 MB CHUNK_SIZE)
+        let mut malicious_plaintext = Vec::new();
+        malicious_plaintext.push(COMPRESSION_LZ4);
+        let fake_uncompressed_size: u32 = 5 * 1024 * 1024; // 5 MB
+        malicious_plaintext.extend_from_slice(&fake_uncompressed_size.to_le_bytes());
+        malicious_plaintext.extend_from_slice(&[0u8; 32]); // Dummy-LZ4-Payload
+
+        let mut nonce_bytes = [0u8; 12];
+        rand::RngCore::fill_bytes(&mut rand::rngs::OsRng, &mut nonce_bytes);
+        let nonce = Nonce::from_slice(&nonce_bytes);
+
+        let mut ct = malicious_plaintext.clone();
+        let tag = cipher.encrypt_in_place_detached(nonce, &aad, &mut ct).unwrap();
+        let tag_bytes: [u8; 16] = tag.as_slice().try_into().unwrap();
+
+        // Entschlüsselung muss fehlschlagen, da Dekomprimierungs-Bomb-Schutz greift
+        let res = decrypt_chunk(&dek, node_id, chunk_index, &ct, &nonce_bytes, &tag_bytes, FORMAT_VERSION_V2);
+        assert!(res.is_err(), "Dekomprimierungs-Bomb über 1 MB muss abgewiesen werden!");
+        let err_msg = res.err().unwrap().to_string();
+        assert!(err_msg.contains("Decompression-Bomb Schutz ausgelöst"), "Fehlermeldung erwartet: {}", err_msg);
+    }
 }