Re: [PATCH] tpm: Check return value of crypto_kpp_set_secret()

[Jarkko Sakkinen <jarkko@kernel.org>]

On Sun, Oct 25, 2026 at 02:11:19PM -0700, Eric Biggers wrote:
> crypto_kpp_set_secret() can fail, for example if the kernel is booted
> with fips=1 and the broken-by-design FIPS RNG used for ECC private key
> generation doesn't feel like generating random bytes at the moment.
> Check for error, cancelling the TPM session creation rather than
> proceeding with a zero or uninitialized private key.
> 
> Fixes: 699e3efd6c64 ("tpm: Add HMAC session start and end functions")
> Cc: stable@vger.kernel.org
> Signed-off-by: Eric Biggers <ebiggers@kernel.org>
> ---
>  drivers/char/tpm/tpm2-sessions.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
> index ca1e2bf424e14..2aaaad69760dc 100644
> --- a/drivers/char/tpm/tpm2-sessions.c
> +++ b/drivers/char/tpm/tpm2-sessions.c
> @@ -527,7 +527,9 @@ static int tpm_buf_append_salt(struct tpm_buf *buf, struct tpm_chip *chip,
>  	}
>  	crypto_ecdh_encode_key(encoded_key, buf_len, &p);
>  	/* this generates a random private key */

Could you delete this comment while at it? It's not helping with
anything.

> -	crypto_kpp_set_secret(kpp, encoded_key, buf_len);
> +	rc = crypto_kpp_set_secret(kpp, encoded_key, buf_len);
> +	if (rc)
> +		goto err_free_kpp;
>  
>  	/* salt is now the public point of this private key */
>  	req = kpp_request_alloc(kpp, GFP_KERNEL);
> 
> base-commit: 21a7f44fd0765fcc5194130b28767786eba1d1e7
> -- 
> 2.56.0
> 

[1] https://lore.kernel.org/linux-integrity/asQdZiv7uktfyRWU@kernel.org/

Br, Jarkko