linux-kernel - Re: [PATCH v2] KEYS: trusted: Fix memory leak in tpm2_key

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Message-ID: <YqCmVi3J10Tcx0Wk@noodles-fedora.dhcp.thefacebook.com>
Date:   Wed, 8 Jun 2022 13:38:35 +0000
From:   Jonathan McDowell <noodles@...com>
To:     Jianglei Nie <niejianglei2021@....com>
CC:     "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "jarkko@...nel.org" <jarkko@...nel.org>,
        "zohar@...ux.ibm.com" <zohar@...ux.ibm.com>,
        "dhowells@...hat.com" <dhowells@...hat.com>,
        "jmorris@...ei.org" <jmorris@...ei.org>,
        "serge@...lyn.com" <serge@...lyn.com>,
        "linux-integrity@...r.kernel.org" <linux-integrity@...r.kernel.org>,
        "keyrings@...r.kernel.org" <keyrings@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] KEYS: trusted: Fix memory leak in tpm2_key_encode()

On Wed, Jun 08, 2022 at 09:17:32PM +0800, 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.

This change only does the kfree in the success path; "out" just returns
the error without freeing the memory.

> Signed-off-by: Jianglei Nie <niejianglei2021@....com>
> ---
>  security/keys/trusted-keys/trusted_tpm2.c | 23 +++++++++++++++++------
>  1 file changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/security/keys/trusted-keys/trusted_tpm2.c b/security/keys/trusted-keys/trusted_tpm2.c
> index 0165da386289..8b7ab22950d1 100644
> --- a/security/keys/trusted-keys/trusted_tpm2.c
> +++ b/security/keys/trusted-keys/trusted_tpm2.c
> @@ -32,6 +32,7 @@ static int tpm2_key_encode(struct trusted_key_payload *payload,
>  			   struct trusted_key_options *options,
>  			   u8 *src, u32 len)
>  {
> +	int err;
>  	const int SCRATCH_SIZE = PAGE_SIZE;
>  	u8 *scratch = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
>  	u8 *work = scratch, *work1;
> @@ -57,8 +58,10 @@ 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"))
> -			return PTR_ERR(w);
> +		if (WARN(IS_ERR(w), "BUG: Boolean failed to encode")) {
> +			err = PTR_ERR(w);
> +			goto out;
> +		}
>  		work = asn1_encode_tag(work, end_work, 0, bool, w - bool);
>  	}
>  
> @@ -69,8 +72,10 @@ 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"))
> -		return -EINVAL;
> +		 "BUG: scratch buffer is too small")) {
> +		err = -EINVAL;
> +		goto out;
> +	}
>  
>  	work = asn1_encode_integer(work, end_work, options->keyhandle);
>  	work = asn1_encode_octet_string(work, end_work, pub, pub_len);
> @@ -79,10 +84,16 @@ 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"))
> -		return PTR_ERR(work1);
> +	if (WARN(IS_ERR(work1), "BUG: ASN.1 encoder failed")) {
> +		err = -EINVAL;
> +		goto out;
> +	}
> +	kfree(scratch);
>  
>  	return work1 - payload->blob;
> +
> +out:
> +	return err;
>  }
>  
>  struct tpm2_key_context {
> -- 
> 2.25.1