KEYS: trusted_tpm1: Compare HMAC values in constant time

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>

diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c
index 89c9798d18007192f30e6cd21605b78cd6cb55d9..e73f2c6c817a07039a5ea576cda6b057c9517d04 100644 (file)
--- 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 *buffer,
                          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 *buffer,
                          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);