linux-kernel - Re: [PATCH] security:trusted_tpm2: Fix memory leak in tpm2_key

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Date:   Tue, 7 Jun 2022 10:34:38 +0200
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     Jianglei Nie <niejianglei2021@....com>, jejb@...ux.ibm.com,
        jarkko@...nel.org, zohar@...ux.ibm.com, dhowells@...hat.com,
        jmorris@...ei.org, serge@...lyn.com
Cc:     linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] security:trusted_tpm2: Fix memory leak in
 tpm2_key_encode()

Hello Jianglei,

On 07.06.22 09:46, Jianglei Nie wrote:
> The function allocates a memory chunk for scratch by kmalloc(), but
> it is never freed through the function, which leads to a memory leak.
> Handle those cases with kfree().

Thanks for your patch.

Shouldn't you free scratch before successful return too?

I haven't looked too deeply, but it looks like scratch is indeed
scratch space and data written to it are memcpy'd elsewhere before
the function returns and no pointer derived from it survives after
function return.

If this is indeed the case, consider also to switch this to a goto out.

Cheers,
Ahmad
  

> 
> Signed-off-by: Jianglei Nie <niejianglei2021@....com>
> ---
>  security/keys/trusted-keys/trusted_tpm2.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
> index 0165da386289..dc9efd6c8b14 100644
> --- a/security/keys/trusted-keys/trusted_tpm2.c
> +++ b/security/keys/trusted-keys/trusted_tpm2.c
> @@ -57,8 +57,10 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
>  		unsigned char bool[3], *w = bool;
>  		/* tag 0 is emptyAuth */
>  		w = asn1_encode_boolean(w, w + sizeof(bool), true);
> -		if (WARN(IS_ERR(w), "BUG: Boolean failed to encode"))
> +		if (WARN(IS_ERR(w), "BUG: Boolean failed to encode")) {
> +			kfree(scratch);
>  			return PTR_ERR(w);
> +		}
>  		work = asn1_encode_tag(work, end_work, 0, bool, w - bool);
>  	}
>  
> @@ -69,8 +71,10 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
>  	 * trigger, so if it does there's something nefarious going on
>  	 */
>  	if (WARN(work - scratch + pub_len + priv_len + 14 > SCRATCH_SIZE,
> -		 "BUG: scratch buffer is too small"))
> +		 "BUG: scratch buffer is too small")) {
> +		kfree(scratch);
>  		return -EINVAL;
> +	}
>  
>  	work = asn1_encode_integer(work, end_work, options->keyhandle);
>  	work = asn1_encode_octet_string(work, end_work, pub, pub_len);
> @@ -79,8 +83,10 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
>  	work1 = payload->blob;
>  	work1 = asn1_encode_sequence(work1, work1 + sizeof(payload->blob),
>  				     scratch, work - scratch);
> -	if (WARN(IS_ERR(work1), "BUG: ASN.1 encoder failed"))
> +	if (WARN(IS_ERR(work1), "BUG: ASN.1 encoder failed")) {
> +		kfree(scratch);
>  		return PTR_ERR(work1);
> +	}
>  
>  	return work1 - payload->blob;
>  }


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