[PATCH 1/2] crypto: keembay - use crypto_memneq() to compare GCM AEAD tags

["David C.C.M. Gall" <david.ccm.gall@googlemail.com>]

Use crypto_memneq() for constant-time comparison.

The GCM path in keembay-ocs-aes-core.c verifes the received
authentication tag with memcmp(), which returns early on the first
mismatched byte. This leaks valid-prefix length and allows for valid
tag forgery which violates the INT-CTXT guarantee of AEAD.

Assisted-by: gregkh_clanker_t1000
Signed-off-by: David C.C.M. Gall <david.ccm.gall@googlemail.com>
---
 drivers/crypto/intel/keembay/keembay-ocs-aes-core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/crypto/intel/keembay/keembay-ocs-aes-core.c b/drivers/crypto/intel/keembay/keembay-ocs-aes-core.c
index 8a8f6c81e010..f8f4517ccad0 100644
--- a/drivers/crypto/intel/keembay/keembay-ocs-aes-core.c
+++ b/drivers/crypto/intel/keembay/keembay-ocs-aes-core.c
@@ -11,6 +11,7 @@
 #include <crypto/internal/aead.h>
 #include <crypto/internal/skcipher.h>
 #include <crypto/scatterwalk.h>
+#include <crypto/utils.h>
 #include <linux/clk.h>
 #include <linux/completion.h>
 #include <linux/dma-mapping.h>
@@ -919,7 +920,7 @@ static int kmb_ocs_aead_run(struct aead_request *req)
 
 	/* For GCM decrypt, we have to compare in_tag with out_tag. */
 	if (rctx->instruction == OCS_DECRYPT) {
-		rc = memcmp(rctx->in_tag, rctx->out_tag, tag_size) ?
+		rc = crypto_memneq(rctx->in_tag, rctx->out_tag, tag_size) ?
 		     -EBADMSG : 0;
 		goto exit;
 	}
-- 
2.43.0