* [PATCH v2 1/3] KEYS: trusted_tpm1: Compare HMAC values in constant time
[not found] <20250809171941.5497-1-ebiggers@kernel.org>
@ 2025-08-09 17:19 ` Eric Biggers
2025-08-12 16:23 ` Jarkko Sakkinen
0 siblings, 1 reply; 2+ messages in thread
From: Eric Biggers @ 2025-08-09 17:19 UTC (permalink / raw)
To: James Bottomley, Jarkko Sakkinen, Mimi Zohar, keyrings
Cc: David Howells, linux-integrity, linux-crypto, linux-kernel,
Eric Biggers, stable
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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH v2 1/3] KEYS: trusted_tpm1: Compare HMAC values in constant time
2025-08-09 17:19 ` [PATCH v2 1/3] KEYS: trusted_tpm1: Compare HMAC values in constant time Eric Biggers
@ 2025-08-12 16:23 ` Jarkko Sakkinen
0 siblings, 0 replies; 2+ messages in thread
From: Jarkko Sakkinen @ 2025-08-12 16:23 UTC (permalink / raw)
To: Eric Biggers
Cc: James Bottomley, Mimi Zohar, keyrings, David Howells,
linux-integrity, linux-crypto, linux-kernel, stable
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
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2025-08-09 17:19 ` [PATCH v2 1/3] KEYS: trusted_tpm1: Compare HMAC values in constant time Eric Biggers
2025-08-12 16:23 ` Jarkko Sakkinen
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