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: sta...@vger.kernel.org
> Signed-off-by: Eric Biggers <ebigg...@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 <jar...@kernel.org>
BR, Jarkko
