X.509: Introduce scope-based x509_certificate allocation

Add a DEFINE_FREE() clause for x509_certificate structs and use it in
x509_cert_parse() and x509_key_preparse().  These are the only functions
where scope-based x509_certificate allocation currently makes sense.
A third user will be introduced with the forthcoming SPDM library
(Security Protocol and Data Model) for PCI device authentication.

Unlike most other DEFINE_FREE() clauses, this one checks for IS_ERR()
instead of NULL before calling x509_free_certificate() at end of scope.
That's because the "constructor" of x509_certificate structs,
x509_cert_parse(), returns a valid pointer or an ERR_PTR(), but never
NULL.

Comparing the Assembler output before/after has shown they are identical,
save for the fact that gcc-12 always generates two return paths when
__cleanup() is used, one for the success case and one for the error case.

In x509_cert_parse(), add a hint for the compiler that kzalloc() never
returns an ERR_PTR().  Otherwise the compiler adds a gratuitous IS_ERR()
check on return.  Introduce an assume() macro for this which can be
re-used elsewhere in the kernel to provide hints for the compiler.

Suggested-by: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
Link: https://lore.kernel.org/all/20231003153937.000034ca@Huawei.com/
Link: https://lwn.net/Articles/934679/
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 16 insertions, 27 deletions

diff --git a/crypto/asymmetric_keys/x509_cert_parser.c b/crypto/asymmetric_keys/x509_cert_parser.c
index 964208d1..a814e5f1 100644
--- a/crypto/asymmetric_keys/x509_cert_parser.c
+++ b/crypto/asymmetric_keys/x509_cert_parser.c
@@ -60,24 +60,24 @@ EXPORT_SYMBOL_GPL(x509_free_certificate);
  */
 struct x509_certificate *x509_cert_parse(const void *data, size_t datalen)
 {
-	struct x509_certificate *cert;
-	struct x509_parse_context *ctx;
+	struct x509_certificate *cert __free(x509_free_certificate);
+	struct x509_parse_context *ctx __free(kfree) = NULL;
 	struct asymmetric_key_id *kid;
 	long ret;
 
-	ret = -ENOMEM;
 	cert = kzalloc(sizeof(struct x509_certificate), GFP_KERNEL);
+	assume(!IS_ERR(cert)); /* Avoid gratuitous IS_ERR() check on return */
 	if (!cert)
-		goto error_no_cert;
+		return ERR_PTR(-ENOMEM);
 	cert->pub = kzalloc(sizeof(struct public_key), GFP_KERNEL);
 	if (!cert->pub)
-		goto error_no_ctx;
+		return ERR_PTR(-ENOMEM);
 	cert->sig = kzalloc(sizeof(struct public_key_signature), GFP_KERNEL);
 	if (!cert->sig)
-		goto error_no_ctx;
+		return ERR_PTR(-ENOMEM);
 	ctx = kzalloc(sizeof(struct x509_parse_context), GFP_KERNEL);
 	if (!ctx)
-		goto error_no_ctx;
+		return ERR_PTR(-ENOMEM);
 
 	ctx->cert = cert;
 	ctx->data = (unsigned long)data;
@@ -85,7 +85,7 @@ struct x509_certificate *x509_cert_parse(const void *data, size_t datalen)
 	/* Attempt to decode the certificate */
 	ret = asn1_ber_decoder(&x509_decoder, ctx, data, datalen);
 	if (ret < 0)
-		goto error_decode;
+		return ERR_PTR(ret);
 
 	/* Decode the AuthorityKeyIdentifier */
 	if (ctx->raw_akid) {
@@ -95,20 +95,19 @@ struct x509_certificate *x509_cert_parse(const void *data, size_t datalen)
 				       ctx->raw_akid, ctx->raw_akid_size);
 		if (ret < 0) {
 			pr_warn("Couldn't decode AuthKeyIdentifier\n");
-			goto error_decode;
+			return ERR_PTR(ret);
 		}
 	}
 
-	ret = -ENOMEM;
 	cert->pub->key = kmemdup(ctx->key, ctx->key_size, GFP_KERNEL);
 	if (!cert->pub->key)
-		goto error_decode;
+		return ERR_PTR(-ENOMEM);
 
 	cert->pub->keylen = ctx->key_size;
 
 	cert->pub->params = kmemdup(ctx->params, ctx->params_size, GFP_KERNEL);
 	if (!cert->pub->params)
-		goto error_decode;
+		return ERR_PTR(-ENOMEM);
 
 	cert->pub->paramlen = ctx->params_size;
 	cert->pub->algo = ctx->key_algo;
@@ -116,33 +115,23 @@ struct x509_certificate *x509_cert_parse(const void *data, size_t datalen)
 	/* Grab the signature bits */
 	ret = x509_get_sig_params(cert);
 	if (ret < 0)
-		goto error_decode;
+		return ERR_PTR(ret);
 
 	/* Generate cert issuer + serial number key ID */
 	kid = asymmetric_key_generate_id(cert->raw_serial,
 					 cert->raw_serial_size,
 					 cert->raw_issuer,
 					 cert->raw_issuer_size);
-	if (IS_ERR(kid)) {
-		ret = PTR_ERR(kid);
-		goto error_decode;
-	}
+	if (IS_ERR(kid))
+		return ERR_CAST(kid);
 	cert->id = kid;
 
 	/* Detect self-signed certificates */
 	ret = x509_check_for_self_signed(cert);
 	if (ret < 0)
-		goto error_decode;
-
-	kfree(ctx);
-	return cert;
+		return ERR_PTR(ret);
 
-error_decode:
-	kfree(ctx);
-error_no_ctx:
-	x509_free_certificate(cert);
-error_no_cert:
-	return ERR_PTR(ret);
+	return_ptr(cert);
 }
 EXPORT_SYMBOL_GPL(x509_cert_parse);