Re: [PATCH] KEYS: trusted: Fix tpm2_load_cmd() boundary check

[Srish Srinivasan <ssrish@linux.ibm.com>]

On 9/2/26 2:28 AM, Jarkko Sakkinen wrote:
> tpm2_load_cmd() does boundary checks against the ASN.1 size i.e.,
> payload->blob_len. Address this by passing the decoded blob size to
> tpm2_load_cmd(), and use it for the boundary checks.
>
> Cc: stable@vger.kernel.org # v5.13+
> Fixes: f2219745250f ("security: keys: trusted: use ASN.1 TPM2 key format for the blobs")
> Reported-by: co+6a581c4284f721d4@bugs.sh
> Closes: https://bugs.sh/b/6a581c4284f721d4/
> Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>


Tested-by: Srish Srinivasan <ssrish@linux.ibm.com>


> ---
>   security/keys/trusted-keys/trusted_tpm2.c | 12 +++++++-----
>   1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
> index 67225dd562a9..01f18bb37047 100644
> --- a/security/keys/trusted-keys/trusted_tpm2.c
> +++ b/security/keys/trusted-keys/trusted_tpm2.c
> @@ -99,7 +99,7 @@ struct tpm2_key_context {
>   
>   static int tpm2_key_decode(struct trusted_key_payload *payload,
>   			   struct trusted_key_options *options,
> -			   u8 **buf)
> +			   u8 **buf, unsigned int *blob_len)
>   {
>   	int ret;
>   	struct tpm2_key_context ctx;
> @@ -120,6 +120,7 @@ static int tpm2_key_decode(struct trusted_key_payload *payload,
>   		return -ENOMEM;
>   
>   	*buf = blob;
> +	*blob_len = ctx.priv_len + ctx.pub_len;
>   	options->keyhandle = ctx.parent;
>   
>   	memcpy(blob, ctx.priv, ctx.priv_len);
> @@ -384,10 +385,11 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
>   	int rc;
>   	u32 attrs;
>   
> -	rc = tpm2_key_decode(payload, options, &blob);
> +	rc = tpm2_key_decode(payload, options, &blob, &blob_len);
>   	if (rc) {
>   		/* old form */
>   		blob = payload->blob;
> +		blob_len = payload->blob_len;
>   		payload->old_format = 1;
>   	} else {
>   		/* Bind for cleanup: */
> @@ -399,17 +401,17 @@ static int tpm2_load_cmd(struct tpm_chip *chip,
>   		return -EINVAL;
>   
>   	/* must be big enough for at least the two be16 size counts */
> -	if (payload->blob_len < 4)
> +	if (blob_len < 4)
>   		return -EINVAL;
>   
>   	private_len = get_unaligned_be16(blob);
>   
>   	/* must be big enough for following public_len */
> -	if (private_len + 2 + 2 > (payload->blob_len))
> +	if (private_len + 2 + 2 > blob_len)
>   		return -E2BIG;
>   
>   	public_len = get_unaligned_be16(blob + 2 + private_len);
> -	if (private_len + 2 + public_len + 2 > payload->blob_len)
> +	if (private_len + 2 + public_len + 2 > blob_len)
>   		return -E2BIG;
>   
>   	pub = blob + 2 + private_len + 2;