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

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Date:   Wed, 8 Jun 2022 10:29:49 +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 08.06.22 04:59, Jianglei Nie wrote:
> tpm2_key_encode() allocates a memory chunk from scratch with kmalloc(),
> but it is never freed, which leads to a memory leak. Free the memory
> chunk with kfree() in the return path.

Repeating my question in your implicit v1:
Are you sure, scratch need not be freed in the successful return case?
asn1_encode_sequence() copies bytes out of scratch into payload->blob,
so it looks like the buffer is unused after function return.

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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