linux-kernel - Re: [PATCH] tpm: Move dereference after NULL check in tpm_buf_check_hmac

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Message-Id: <D2QW8VSPX777.34R28W8GVXKMS@kernel.org>
Date: Tue, 16 Jul 2024 13:33:17 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Hao Ge" <hao.ge@...ux.dev>, <peterhuewe@....de>, <jgg@...pe.ca>
Cc: <linux-integrity@...r.kernel.org>, <linux-kernel@...r.kernel.org>, "Hao
 Ge" <gehao@...inos.cn>
Subject: Re: [PATCH] tpm: Move dereference after NULL check in
 tpm_buf_check_hmac_response

On Tue Jul 9, 2024 at 5:33 AM EEST, Hao Ge wrote:
> From: Hao Ge <gehao@...inos.cn>
>
> We shouldn't dereference "auth" until after we have checked that it is
> non-NULL.
>
> Fixes: 7ca110f2679b ("tpm: Address !chip->auth in tpm_buf_append_hmac_session*()")
> Signed-off-by: Hao Ge <gehao@...inos.cn>
> ---
>  drivers/char/tpm/tpm2-sessions.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm2-sessions.c b/drivers/char/tpm/tpm2-sessions.c
> index 2281d55df545..d3521aadd43e 100644
> --- a/drivers/char/tpm/tpm2-sessions.c
> +++ b/drivers/char/tpm/tpm2-sessions.c
> @@ -746,15 +746,16 @@ int tpm_buf_check_hmac_response(struct tpm_chip *chip, struct tpm_buf *buf,
>  	struct tpm2_auth *auth = chip->auth;
>  	off_t offset_s, offset_p;
>  	u8 rphash[SHA256_DIGEST_SIZE];
> -	u32 attrs;
> +	u32 attrs, cc;
>  	struct sha256_state sctx;
>  	u16 tag = be16_to_cpu(head->tag);
> -	u32 cc = be32_to_cpu(auth->ordinal);
>  	int parm_len, len, i, handles;
>  
>  	if (!auth)
>  		return rc;
>  
> +	cc = be32_to_cpu(auth->ordinal);
> +
>  	if (auth->session >= TPM_HEADER_SIZE) {
>  		WARN(1, "tpm session not filled correctly\n");
>  		goto out;

Please check:

https://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd.git/commit/?id=72d6e06ed101e31e943937e42053fc690dc75cfe

It is exactly this except commit message is tuned. And please denote
that I'm on holiday ;-)

If that works for you, I can put it to my -rc PR.

Thank you.

BR, Jarkko