On Sun, Sep 24, 2017 at 08:25:17AM +0200, Stephan Müller wrote:
> In case the caller provides an SG with zero data, prevent a kmap of the
> page pointed to by the SG. In this case, it is possible that the page
> does not exist.
>
> This fixes a crash in authenc() when the plaintext is zero and thus the
> encryption operation is a noop. In this case, no input data exists that
> can be hashed. The crash is triggerable via AF_ALG from unprivileged
> user space.
>
> Fixes: 3b2f6df08258e ("crypto: hash - Export shash through ahash")
> CC: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
> CC: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Stephan Mueller <smueller@xxxxxxxxxx>
> ---
> crypto/shash.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/crypto/shash.c b/crypto/shash.c
> index 5e31c8d776df..32d0e1806bf4 100644
> --- a/crypto/shash.c
> +++ b/crypto/shash.c
> @@ -278,9 +278,11 @@ int shash_ahash_digest(struct ahash_request *req, struct shash_desc *desc)
> struct scatterlist *sg = req->src;
> unsigned int offset = sg->offset;
> unsigned int nbytes = req->nbytes;
> + unsigned int process = min(sg->length,
> + ((unsigned int)(PAGE_SIZE)) - offset);
> int err;
>
> - if (nbytes < min(sg->length, ((unsigned int)(PAGE_SIZE)) - offset)) {
> + if (process && nbytes < process) {
Sorry but your patch makes no sense. The only difference between
your patch and the status quo is when process == zero. However,
if process is zero then the if condition cannot hold since it's
an unsigned comparison. So how can this patch make any difference
at all?
Cheers,
--
Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
