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

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Message-ID: <YqGE/v0Zgi+g4gY6@iki.fi>
Date:   Thu, 9 Jun 2022 08:28:30 +0300
From:   "jarkko@...nel.org" <jarkko@...nel.org>
To:     Jonathan McDowell <noodles@...com>
Cc:     Jianglei Nie <niejianglei2021@....com>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "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 01:38:35PM +0000, Jonathan McDowell wrote:
> 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.

A valid point.

> > 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);

Also, the fix is half-way there, it does not have OOM
check for scratch.

I.e. I'd change the declaration as:

        u8 *scratch;

And later on after declarations:

        scratch = kmalloc(SCRATCH_SIZE, GFP_KERNEL);
        if (!scratch)
                return -ENOMEM; 

> >  	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;

I.e.

        kfree(scratch);
        return work1 - payload->blob;

err:
        kfree(scratch);
        return ret;


> >  }
> >  
> >  struct tpm2_key_context {
> > -- 
> > 2.25.1

BR, Jarkko