On Thu, Nov 22, 2018 at 10:44:41PM +0800, Herbert Xu wrote: > On Thu, Nov 22, 2018 at 06:00:16PM +0800, Pan Bian wrote: > > In multiple functions, the algorithm fields are read after its reference > > is dropped through crypto_mod_put. In this case, the algorithm memory > > may be freed, resulting in use-after-free bugs. This patch delays the > > put operation until the algorithm is never used. > > > > Signed-off-by: Pan Bian <bianpan2016@xxxxxxx> > > I don't think this patch is needed. > > > --- > > crypto/cbc.c | 6 ++++-- > > crypto/cfb.c | 6 ++++-- > > crypto/pcbc.c | 6 ++++-- > > 3 files changed, 12 insertions(+), 6 deletions(-) > > > > diff --git a/crypto/cbc.c b/crypto/cbc.c > > index b761b1f..dd5f332 100644 > > --- a/crypto/cbc.c > > +++ b/crypto/cbc.c > > @@ -140,9 +140,8 @@ static int crypto_cbc_create(struct crypto_template *tmpl, struct rtattr **tb) > > spawn = skcipher_instance_ctx(inst); > > err = crypto_init_spawn(spawn, alg, skcipher_crypto_instance(inst), > > CRYPTO_ALG_TYPE_MASK); > > - crypto_mod_put(alg); > > if (err) > > - goto err_free_inst; > > + goto err_put_alg; > > We can safely drop the reference to the algorithm because the spawn > is now meant to hold a reference to it. As long as the spawn is > alive so will the algorithm. Thanks for your explanation! But I find that the function crypto_init_spawn just lets spawn->alg point to the algorithm without increasing the reference count, i.e., alg->cra_refcnt. So I am confused about how this can protect the algorithm from being freed. Maybe I missed some key points. Could you please explain it in more details? Thank you! Best regards, Pan Bian > > Cheers, > -- > Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> > Home Page: http://gondor.apana.org.au/~herbert/ > PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
