crypto: x86/aesni-gcm - fix crash on empty plaintext

gcmaes_crypt_by_sg() dereferences the NULL pointer returned by
scatterwalk_ffwd() when encrypting an empty plaintext and the source
scatterlist ends immediately after the associated data.

Fix it by only fast-forwarding to the src/dst data scatterlists if the
data length is nonzero.

This bug is reproduced by the "rfc4543(gcm(aes))" test vectors when run
with the new AEAD test manager.

Fixes: e845520707f8 ("crypto: aesni - Update aesni-intel_glue to use scatter/gather")
Cc: <stable@vger.kernel.org> # v4.17+
Cc: Dave Watson <davejwatson@fb.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/arch/x86/crypto/aesni-intel_glue.c b/arch/x86/crypto/aesni-intel_glue.c
index 9b5ccde..1e3d210 100644 (file)
--- a/arch/x86/crypto/aesni-intel_glue.c
+++ b/arch/x86/crypto/aesni-intel_glue.c
@@ -813,11 +813,14 @@ static int gcmaes_crypt_by_sg(bool enc, struct aead_request *req,
                scatterwalk_map_and_copy(assoc, req->src, 0, assoclen, 0);
        }
 
-       src_sg = scatterwalk_ffwd(src_start, req->src, req->assoclen);
-       scatterwalk_start(&src_sg_walk, src_sg);
-       if (req->src != req->dst) {
-               dst_sg = scatterwalk_ffwd(dst_start, req->dst, req->assoclen);
-               scatterwalk_start(&dst_sg_walk, dst_sg);
+       if (left) {
+               src_sg = scatterwalk_ffwd(src_start, req->src, req->assoclen);
+               scatterwalk_start(&src_sg_walk, src_sg);
+               if (req->src != req->dst) {
+                       dst_sg = scatterwalk_ffwd(dst_start, req->dst,
+                                                 req->assoclen);
+                       scatterwalk_start(&dst_sg_walk, dst_sg);
+               }
        }
 
        kernel_fpu_begin();