From 52e2bde16f5c1e28056ef2de49e046d76b3fb059 Mon Sep 17 00:00:00 2001
From: Fabio Alessandrelli <fabio.alessandrelli@gmail.com>
Date: Mon, 18 Sep 2023 21:06:15 +0200
Subject: [PATCH] [Crypto] Fix generate_random_bytes for large chunks

Properly handle mbedtls errors, ensure we don't ask more bytes than
allowed for each iteration.

(cherry picked from commit e0140601a521e58bb36fd2a7f4b78f1bcb393389)
---
 modules/mbedtls/crypto_mbedtls.cpp | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/modules/mbedtls/crypto_mbedtls.cpp b/modules/mbedtls/crypto_mbedtls.cpp
index 47c0dc9bb6a..de6dfbe0d26 100644
--- a/modules/mbedtls/crypto_mbedtls.cpp
+++ b/modules/mbedtls/crypto_mbedtls.cpp
@@ -419,9 +419,19 @@ Ref<X509Certificate> CryptoMbedTLS::generate_self_signed_certificate(Ref<CryptoK
 }
 
 PackedByteArray CryptoMbedTLS::generate_random_bytes(int p_bytes) {
+	ERR_FAIL_COND_V(p_bytes < 0, PackedByteArray());
 	PackedByteArray out;
 	out.resize(p_bytes);
-	mbedtls_ctr_drbg_random(&ctr_drbg, out.ptrw(), p_bytes);
+	int left = p_bytes;
+	int pos = 0;
+	// Ensure we generate random in chunks of no more than MBEDTLS_CTR_DRBG_MAX_REQUEST bytes or mbedtls_ctr_drbg_random will fail.
+	while (left > 0) {
+		int to_read = MIN(left, MBEDTLS_CTR_DRBG_MAX_REQUEST);
+		int ret = mbedtls_ctr_drbg_random(&ctr_drbg, out.ptrw() + pos, to_read);
+		ERR_FAIL_COND_V_MSG(ret != 0, PackedByteArray(), vformat("Failed to generate %d random bytes(s). Error: %d.", p_bytes, ret));
+		left -= to_read;
+		pos += to_read;
+	}
 	return out;
 }