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SubjectRe: Re: Re: [PATCH] evm: Fix memleak in init_desc
> On Sun, Jan 10, 2021 at 01:27:09PM +0800, dinghao.liu@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@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.
>

Thank you for your advice! I will resend a new patch soon.

Regards,
Dinghao
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