Re: [PATCH 2/2] keys: trusted: tpm1: reject unauthenticated response tag in TSS_checkhmac1/2

[Jarkko Sakkinen]

On Tue, Aug 25, 2026 at 06:29:19PM +0000, sn0x-sharma wrote:
> TSS_checkhmac1() and TSS_checkhmac2() silently return success when the
> response tag is TPM_TAG_RSP_COMMAND (0x00c4), bypassing HMAC
> verification entirely. A forged TPM response with this unauthenticated
> tag allows an attacker to skip integrity checks on TPM responses.
> 
> Reject TPM_TAG_RSP_COMMAND with -EINVAL in both functions, requiring
> all responses to carry a proper authenticated tag.
> 
> Reported-by: sn0x-sharma <sanketsharmacsec@xxxxxxxxx>

SOB is enough.

> Link: https://lore.kernel.org/linux-integrity/
> Signed-off-by: sn0x-sharma <sanketsharmacsec@xxxxxxxxx>

If by any means possible, use your real name here.

> ---
>  security/keys/trusted-keys/trusted_tpm1.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c
> index d47cb7108..c89fc6cfe 100644
> --- a/security/keys/trusted-keys/trusted_tpm1.c
> +++ b/security/keys/trusted-keys/trusted_tpm1.c
> @@ -202,7 +202,7 @@ static int TSS_checkhmac1(unsigned char *buffer,
>  	ordinal = command;
>  	result = LOAD32N(buffer, TPM_RETURN_OFFSET);
>  	if (tag == TPM_TAG_RSP_COMMAND)
> -		return 0;
> +		return -EINVAL;
>  	if (tag != TPM_TAG_RSP_AUTH1_COMMAND)
>  		return -EINVAL;
>  	authdata = buffer + bufsize - SHA1_DIGEST_SIZE;
> @@ -270,7 +270,7 @@ static int TSS_checkhmac2(unsigned char *buffer,
>  	result = LOAD32N(buffer, TPM_RETURN_OFFSET);
>  
>  	if (tag == TPM_TAG_RSP_COMMAND)
> -		return 0;
> +		return -EINVAL;
>  	if (tag != TPM_TAG_RSP_AUTH2_COMMAND)
>  		return -EINVAL;
>  	authdata1 = buffer + bufsize - (SHA1_DIGEST_SIZE + 1
> -- 
> 2.53.0
> 

otherwise looks ok

BR, Jarkko