Re: [PATCH] crypto: arm64/sm4 - Fix possible crash in GCM cryption

[Tianjia Zhang]

Hi Herbert,

On 1/18/23 10:54 PM, Herbert Xu wrote:
> On Wed, Jan 18, 2023 at 10:19:28PM +0800, Tianjia Zhang wrote:
> > When the cryption total length is zero, GCM cryption call
> > skcipher_walk_done() will cause an unexpected crash, so skip calling
> > this function to avoid possible crash when the GCM cryption length
> > is equal to zero.
> >
> > Fixes: ae1b83c7d572 ("crypto: arm64/sm4 - add CE implementation for GCM mode")
> > Signed-off-by: Tianjia Zhang <tianjia.zhang@xxxxxxxxxxxxxxxxx>
> > ---
> >   arch/arm64/crypto/sm4-ce-gcm-glue.c | 12 +++++++-----
> >   1 file changed, 7 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/arm64/crypto/sm4-ce-gcm-glue.c b/arch/arm64/crypto/sm4-ce-gcm-glue.c
> > index c450a2025ca9..9b63bcf9aa85 100644
> > --- a/arch/arm64/crypto/sm4-ce-gcm-glue.c
> > +++ b/arch/arm64/crypto/sm4-ce-gcm-glue.c
> > @@ -178,11 +178,13 @@ static int gcm_crypt(struct aead_request *req, struct skcipher_walk *walk,
> >   
> >   		kernel_neon_end();
> >   
> > -		err = skcipher_walk_done(walk, tail);
> > -		if (err)
> > -			return err;
> > -		if (walk->nbytes)
> > -			kernel_neon_begin();
> > +		if (walk->nbytes) {
>
> Please do
> 		if (!walk->nbytes)
> 			break;

Thanks for the suggestion, a new patch has been sent.

> As an additional improvement, the tail calculation can be removed
> entirely because you already set the chunksize so the walker should
> only be feeding you multiples of chunksize except at the end.
>
> Cheers
I printed the walk->nbytes of each iteration of the walker, it is not
always multiples of chunksize except at the end when the algorithm test
manager is turned on.

For example, during a GCM encryption process, I get data like this:

    total = 4014, nbytes = 2078, tail = 14
    total = 1950, nbytes = 16, tail = 0
    total = 1934, nbytes = 311, tail = 7
    total = 1630, nbytes = 16, tail = 0
    total = 1614, nbytes = 16, tail = 0
    total = 1598, nbytes = 1598, tail = 14

Is my understanding wrong?

Best regards,
Tianjia