[CRYPTO] scatterwalk: Handle zero nbytes in scatterwalk_map_and_copy

It's better to return silently than crash and burn when someone feeds us
a zero length.  In particular the null digest algorithm when used as part
of authenc will do that to us.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/crypto/scatterwalk.c b/crypto/scatterwalk.c
index 297e19d..9aeeb52 100644 (file)
--- a/crypto/scatterwalk.c
+++ b/crypto/scatterwalk.c
@@ -105,6 +105,9 @@ void scatterwalk_map_and_copy(void *buf, struct scatterlist *sg,
        struct scatter_walk walk;
        unsigned int offset = 0;
 
+       if (!nbytes)
+               return;
+
        for (;;) {
                scatterwalk_start(&walk, sg);