On Sat, Aug 09, 2025 at 10:19:39AM -0700, Eric Biggers wrote:

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

---

security/keys/trusted-keys/trusted_tpm1.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c index 89c9798d18007..e73f2c6c817a0 100644 --- a/security/keys/trusted-keys/trusted_tpm1.c +++ b/security/keys/trusted-keys/trusted_tpm1.c @@ -5,10 +5,11 @@

• See Documentation/security/keys/trusted-encrypted.rst

*/ #include <crypto/hash_info.h> +#include <crypto/utils.h> #include <linux/init.h> #include <linux/slab.h> #include <linux/parser.h> #include <linux/string.h> #include <linux/err.h> @@ -239,11 +240,11 @@ int TSS_checkhmac1(unsigned char *buffer, TPM_NONCE_SIZE, enonce, TPM_NONCE_SIZE, ononce, 1, continueflag, 0, 0); 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); return ret; } @@ -332,20 +333,20 @@ static int TSS_checkhmac2(unsigned char *buffer, ret = TSS_rawhmac(testhmac1, key1, keylen1, SHA1_DIGEST_SIZE, paramdigest, TPM_NONCE_SIZE, enonce1, 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; } ret = TSS_rawhmac(testhmac2, key2, keylen2, SHA1_DIGEST_SIZE, paramdigest, TPM_NONCE_SIZE, enonce2, 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); return ret; } -- 2.50.1

Reviewed-by: Jarkko Sakkinen jarkko@kernel.org

BR, Jarkko