Re: dm crypt: Fix reqsize in crypt_iv_eboiv_gen

[Mike Snitzer <snitzer@kernel.org>]

On Thu, Oct 05 2023 at  9:41P -0400,
Herbert Xu <herbert@gondor.apana.org.au> wrote:

> On Fri, Oct 06, 2023 at 08:04:18AM +0700, Bagas Sanjaya wrote:
> >
> > > Git bisect lead me to:
> > > # first bad commit: [e3023094dffb41540330fb0c74cd3a019cd525c2] dm crypt:
> > > Avoid using MAX_CIPHER_BLOCKSIZE
> > > 
> > > If I git revert e3023094dffb41540330fb0c74cd3a019cd525c2 on current Linus'
> > > git master, the issue goes away. So I'm personally not all that affected
> > > anymore (if I'm ready to compile my kernels from now on), and I understand
> > > that you have no clear way to reproduce this as it seems strongly bound to
> > > hardware, but seems like this could point to a potentially serious security
> > > issue since it involves both crypto and undefined behaviour.
> 
> Thanks for the report.  Sorry this is indeed my fault.  The allocated
> buffer is too small as it's missing the size for the request object
> itself.
> 
> Mike, would you be OK with me picking this fix up and pushing it to
> Linus?
> 
> Cheers,
> 
> ---8<---
> A skcipher_request object is made up of struct skcipher_request
> followed by a variable-sized trailer.  The allocation of the
> skcipher_request and IV in crypt_iv_eboiv_gen is missing the
> memory for struct skcipher_request.  Fix it by adding it to
> reqsize.
> 
> Fixes: e3023094dffb ("dm crypt: Avoid using MAX_CIPHER_BLOCKSIZE")
> Reported-by: Tatu Heikkil� <tatu.heikkila@gmail.com>
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
> 
> diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
> index f2662c21a6df..5315fd261c23 100644
> --- a/drivers/md/dm-crypt.c
> +++ b/drivers/md/dm-crypt.c
> @@ -753,7 +753,8 @@ static int crypt_iv_eboiv_gen(struct crypt_config *cc, u8 *iv,
>  	int err;
>  	u8 *buf;
>  
> -	reqsize = ALIGN(crypto_skcipher_reqsize(tfm), __alignof__(__le64));
> +	reqsize = sizeof(*req) + crypto_skcipher_reqsize(tfm);
> +	reqsize = ALIGN(reqsize, __alignof__(__le64));
>  
>  	req = kmalloc(reqsize + cc->iv_size, GFP_NOIO);
>  	if (!req)

Sure, please do.  Shouldn't your header Cc: stable given that the
Fixes commit implies v6.5 needs this fix?

(sorry I missed this the first time I 'Reviewed-by' the original
commit)

Reviewed-by: Mike Mike Snitzer <snitzer@kernel.org>

Thanks,
Mike