[PATCH] evm: Fix memleak in init_desc

[Eric Biggers]

On Sun, Jan 10, 2021 at 01:27:09PM +0800, dinghao.liu at zju.edu.cn wrote:
> > 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 at zju.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?
> 

No.  It does &tfm->base, not tfm->base.

- Eric