crypto: mbedtls_shim: Fix concurrency and deadlock issues

- **Fix session mutex handling:** Ensure the `mtls_sessions_lock` is
    always released in `mtls_get_unused_session_index` on failure
    to prevent deadlocks.
- **Protect `in_use` flag:** Added mutex protection when setting
    `in_use = false` in free functions.
- **Cleanup on setup failure:** Added calls to `mbedtls_*_free()`
    in `mtls_session_setup()` when key initialization fails.
- **Free logic fix:** Corrected `if/else` structure in
    `mtls_session_free()` to ensure the correct context is freed.

Signed-off-by: Badr Bacem KAABIA <[email protected]>

Author: kaabia

drivers/crypto/crypto_mtls_shim.c

@@ -57,6 +57,8 @@ struct mtls_shim_session {
 
 struct mtls_shim_session mtls_sessions[CRYPTO_MAX_SESSION];
 
+static K_MUTEX_DEFINE(mtls_sessions_lock);
+
 #if defined(MBEDTLS_MEMORY_BUFFER_ALLOC_C)
 #include "mbedtls/memory_buffer_alloc.h"
 #else
@@ -295,13 +297,17 @@ static int mtls_get_unused_session_index(void)
 {
 	int i;
 
+	k_mutex_lock(&mtls_sessions_lock, K_FOREVER);
+
 	for (i = 0; i < CRYPTO_MAX_SESSION; i++) {
 		if (!mtls_sessions[i].in_use) {
 			mtls_sessions[i].in_use = true;
+			k_mutex_unlock(&mtls_sessions_lock);
 			return i;
 		}
 	}
 
+	k_mutex_unlock(&mtls_sessions_lock);
 	return -1;
 }
 
@@ -316,7 +322,7 @@ static int mtls_session_setup(const struct device *dev,
 	mbedtls_gcm_context *gcm_ctx;
 #endif
 	int ctx_idx;
-	int ret;
+	int ret = 0;
 
 	if (ctx->flags & ~(MTLS_SUPPORT)) {
 		LOG_ERR("Unsupported flag");
@@ -349,6 +355,8 @@ static int mtls_session_setup(const struct device *dev,
 		return -ENOSPC;
 	}
 
+	mtls_sessions[ctx_idx].mode = mode;
+	ctx->drv_sessn_state = &mtls_sessions[ctx_idx];
 
 	switch (mode) {
 	case CRYPTO_CIPHER_MODE_ECB:
@@ -365,9 +373,8 @@ static int mtls_session_setup(const struct device *dev,
 		}
 		if (ret) {
 			LOG_ERR("AES_ECB: failed at setkey (%d)", ret);
-			ctx->ops.block_crypt_hndlr = NULL;
-			mtls_sessions[ctx_idx].in_use = false;
-			return -EINVAL;
+			mbedtls_aes_free(aes_ctx);
+			ret = -EINVAL;
 		}
 		break;
 	case CRYPTO_CIPHER_MODE_CBC:
@@ -384,9 +391,8 @@ static int mtls_session_setup(const struct device *dev,
 		}
 		if (ret) {
 			LOG_ERR("AES_CBC: failed at setkey (%d)", ret);
-			ctx->ops.cbc_crypt_hndlr = NULL;
-			mtls_sessions[ctx_idx].in_use = false;
-			return -EINVAL;
+			mbedtls_aes_init(aes_ctx);
+			ret = -EINVAL;
 		}
 		break;
 	case CRYPTO_CIPHER_MODE_CCM:
@@ -396,9 +402,9 @@ static int mtls_session_setup(const struct device *dev,
 					 ctx->key.bit_stream, ctx->keylen * 8U);
 		if (ret) {
 			LOG_ERR("AES_CCM: failed at setkey (%d)", ret);
-			mtls_sessions[ctx_idx].in_use = false;
-
-			return -EINVAL;
+			mbedtls_ccm_free(ccm_ctx);
+			ret = -EINVAL;
+			break;
 		}
 		if (op_type == CRYPTO_CIPHER_OP_ENCRYPT) {
 			ctx->ops.ccm_crypt_hndlr = mtls_ccm_encrypt_auth;
@@ -414,9 +420,9 @@ static int mtls_session_setup(const struct device *dev,
 					 ctx->key.bit_stream, ctx->keylen * 8U);
 		if (ret) {
 			LOG_ERR("AES_GCM: failed at setkey (%d)", ret);
-			mtls_sessions[ctx_idx].in_use = false;
-
-			return -EINVAL;
+			mbedtls_gcm_free(gcm_ctx);
+			ret = -EINVAL;
+			break;
 		}
 		if (op_type == CRYPTO_CIPHER_OP_ENCRYPT) {
 			ctx->ops.gcm_crypt_hndlr = mtls_gcm_encrypt_auth;
@@ -427,13 +433,17 @@ static int mtls_session_setup(const struct device *dev,
 #endif /* CONFIG_MBEDTLS_CIPHER_GCM_ENABLED */
 	default:
 		LOG_ERR("Unhandled mode");
-		mtls_sessions[ctx_idx].in_use = false;
-		return -EINVAL;
+		ret = -EINVAL;
 	}
 
-	mtls_sessions[ctx_idx].mode = mode;
-	ctx->drv_sessn_state = &mtls_sessions[ctx_idx];
-
+	/* Centralized cleanup of the session slot if an error occurred
+	 *  during configuration (ret != 0).
+	 */
+	if (ret != 0) {
+		k_mutex_lock(&mtls_sessions_lock, K_FOREVER);
+		mtls_sessions[ctx_idx].in_use = false;
+		k_mutex_unlock(&mtls_sessions_lock);
+	}
 	return ret;
 }
 
@@ -451,7 +461,9 @@ static int mtls_session_free(const struct device *dev, struct cipher_ctx *ctx)
 	} else {
 		mbedtls_aes_free(&mtls_session->mtls_aes);
 	}
+	k_mutex_lock(&mtls_sessions_lock, K_FOREVER);
 	mtls_session->in_use = false;
+	k_mutex_unlock(&mtls_sessions_lock);
 
 	return 0;
 }
@@ -582,7 +594,9 @@ static int mtls_hash_session_free(const struct device *dev, struct hash_ctx *ctx
 	} else {
 		mbedtls_sha512_free(&mtls_session->mtls_sha512);
 	}
+	k_mutex_lock(&mtls_sessions_lock, K_FOREVER);
 	mtls_session->in_use = false;
+	k_mutex_unlock(&mtls_sessions_lock);
 
 	return 0;
 }