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Date:   Sun, 10 Jan 2021 13:27:09 +0800 (GMT+08:00)
From:   dinghao.liu@....edu.cn
To:     "Eric Biggers" <ebiggers@...nel.org>
Cc:     kjlu@....edu, "Mimi Zohar" <zohar@...ux.ibm.com>,
        "James Morris" <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        "Dmitry Kasatkin" <dmitry.kasatkin@...ia.com>,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH] evm: Fix memleak in init_desc

> On Sat, Jan 09, 2021 at 07:33:05PM +0800, Dinghao Liu wrote:
> > When kmalloc() fails, tmp_tfm allocated by
> > crypto_alloc_shash() has not been freed, which
> > leads to memleak.
> > 
> > Fixes: d46eb3699502b ("evm: crypto hash replaced by shash")
> > Signed-off-by: Dinghao Liu <dinghao.liu@....edu.cn>
> > ---
> >  security/integrity/evm/evm_crypto.c | 9 +++++++--
> >  1 file changed, 7 insertions(+), 2 deletions(-)
> > 
> > diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
> > index 168c3b78ac47..39fb31a638ac 100644
> > --- a/security/integrity/evm/evm_crypto.c
> > +++ b/security/integrity/evm/evm_crypto.c
> > @@ -73,7 +73,7 @@ static struct shash_desc *init_desc(char type, uint8_t hash_algo)
> >  {
> >  	long rc;
> >  	const char *algo;
> > -	struct crypto_shash **tfm, *tmp_tfm;
> > +	struct crypto_shash **tfm, *tmp_tfm = NULL;
> >  	struct shash_desc *desc;
> >  
> >  	if (type == EVM_XATTR_HMAC) {
> > @@ -118,13 +118,18 @@ static struct shash_desc *init_desc(char type, uint8_t hash_algo)
> >  alloc:
> >  	desc = kmalloc(sizeof(*desc) + crypto_shash_descsize(*tfm),
> >  			GFP_KERNEL);
> > -	if (!desc)
> > +	if (!desc) {
> > +		if (tmp_tfm)
> > +			crypto_free_shash(tmp_tfm);
> >  		return ERR_PTR(-ENOMEM);
> > +	}
> >  
> >  	desc->tfm = *tfm;
> >  
> >  	rc = crypto_shash_init(desc);
> >  	if (rc) {
> > +		if (tmp_tfm)
> > +			crypto_free_shash(tmp_tfm);
> >  		kfree(desc);
> >  		return ERR_PTR(rc);
> >  	}
> 
> There's no need to check for NULL before calling crypto_free_shash().
> 

I find there is a crypto_shash_tfm() in the definition of 
crypto_free_shash(). Will this lead to null pointer dereference
when we use it to free a NULL pointer?

Regards,
Dinghao

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