[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>

1 files changed, 3 insertions, 0 deletions

diff --git a/crypto/scatterwalk.c b/crypto/scatterwalk.c
index 297e19d13c4e..9aeeb52004a5 100644
--- 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);