releases/6.17.4/keys-trusted_tpm1-compare-hmac-values-in-constant-time.patch

From eed0e3d305530066b4fc5370107cff8ef1a0d229 Mon Sep 17 00:00:00 2001
From: Eric Biggers <ebiggers@kernel.org>
Date: Sat, 9 Aug 2025 10:19:39 -0700
Subject: KEYS: trusted_tpm1: Compare HMAC values in constant time

From: Eric Biggers <ebiggers@kernel.org>

commit eed0e3d305530066b4fc5370107cff8ef1a0d229 upstream.

To prevent timing attacks, HMAC value comparison needs to be constant
time.  Replace the memcmp() with the correct function, crypto_memneq().

[For the Fixes commit I used the commit that introduced the memcmp().
It predates the introduction of crypto_memneq(), but it was still a bug
at the time even though a helper function didn't exist yet.]

Fixes: d00a1c72f7f4 ("keys: add new trusted key-type")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 security/keys/trusted-keys/trusted_tpm1.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/security/keys/trusted-keys/trusted_tpm1.c
+++ b/security/keys/trusted-keys/trusted_tpm1.c
@@ -7,6 +7,7 @@
  */
 
 #include <crypto/hash_info.h>
+#include <crypto/utils.h>
 #include <linux/init.h>
 #include <linux/slab.h>
 #include <linux/parser.h>
@@ -241,7 +242,7 @@ int TSS_checkhmac1(unsigned char *buffer
 	if (ret < 0)
 		goto out;
 
-	if (memcmp(testhmac, authdata, SHA1_DIGEST_SIZE))
+	if (crypto_memneq(testhmac, authdata, SHA1_DIGEST_SIZE))
 		ret = -EINVAL;
 out:
 	kfree_sensitive(sdesc);
@@ -334,7 +335,7 @@ static int TSS_checkhmac2(unsigned char
 			  TPM_NONCE_SIZE, ononce, 1, continueflag1, 0, 0);
 	if (ret < 0)
 		goto out;
-	if (memcmp(testhmac1, authdata1, SHA1_DIGEST_SIZE)) {
+	if (crypto_memneq(testhmac1, authdata1, SHA1_DIGEST_SIZE)) {
 		ret = -EINVAL;
 		goto out;
 	}
@@ -343,7 +344,7 @@ static int TSS_checkhmac2(unsigned char
 			  TPM_NONCE_SIZE, ononce, 1, continueflag2, 0, 0);
 	if (ret < 0)
 		goto out;
-	if (memcmp(testhmac2, authdata2, SHA1_DIGEST_SIZE))
+	if (crypto_memneq(testhmac2, authdata2, SHA1_DIGEST_SIZE))
 		ret = -EINVAL;
 out:
 	kfree_sensitive(sdesc);