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SubjectRe: 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@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?

Regards,
Dinghao
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