On 4 September 2018 at 20:16, Kees Cook <keescook@xxxxxxxxxxxx> wrote: > In the quest to remove all stack VLA usage from the kernel[1], this > caps the skcipher request size similar to other limits and adds a sanity > check at registration. Looking at instrumented tcrypt output, the largest > is for lrw: > > crypt: testing lrw(aes) > crypto_skcipher_set_reqsize: 8 > crypto_skcipher_set_reqsize: 88 > crypto_skcipher_set_reqsize: 472 > Are you sure this is a representative sampling? I haven't double checked myself, but we have plenty of drivers for peripherals in drivers/crypto that implement block ciphers, and they would not turn up in tcrypt unless you are running on a platform that provides the hardware in question. > [1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@xxxxxxxxxxxxxx > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > --- > include/crypto/internal/skcipher.h | 3 +++ > include/crypto/skcipher.h | 4 +++- > 2 files changed, 6 insertions(+), 1 deletion(-) > > diff --git a/include/crypto/internal/skcipher.h b/include/crypto/internal/skcipher.h > index d2926ecae2ac..6da811c0747e 100644 > --- a/include/crypto/internal/skcipher.h > +++ b/include/crypto/internal/skcipher.h > @@ -130,6 +130,9 @@ static inline struct crypto_skcipher *crypto_spawn_skcipher( > static inline int crypto_skcipher_set_reqsize( > struct crypto_skcipher *skcipher, unsigned int reqsize) > { > + if (WARN_ON(reqsize > SKCIPHER_MAX_REQSIZE)) > + return -EINVAL; > + > skcipher->reqsize = reqsize; > > return 0; > diff --git a/include/crypto/skcipher.h b/include/crypto/skcipher.h > index 2f327f090c3e..c48e194438cf 100644 > --- a/include/crypto/skcipher.h > +++ b/include/crypto/skcipher.h > @@ -139,9 +139,11 @@ struct skcipher_alg { > struct crypto_alg base; > }; > > +#define SKCIPHER_MAX_REQSIZE 472 > + > #define SKCIPHER_REQUEST_ON_STACK(name, tfm) \ > char __##name##_desc[sizeof(struct skcipher_request) + \ > - crypto_skcipher_reqsize(tfm)] CRYPTO_MINALIGN_ATTR; \ > + SKCIPHER_MAX_REQSIZE] CRYPTO_MINALIGN_ATTR; \ > struct skcipher_request *name = (void *)__##name##_desc > > /** > -- > 2.17.1 >
