[PATCH 4.12 15/31] crypto: authencesn - Fix digest_null crash

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

4.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Herbert Xu <herbert@gondor.apana.org.au>

commit 41cdf7a45389e01991ee31e3301ed83cb3e3f7dc upstream.

When authencesn is used together with digest_null a crash will
occur on the decrypt path.  This is because normally we perform
a special setup to preserve the ESN, but this is skipped if there
is no authentication.  However, on the post-authentication path
it always expects the preservation to be in place, thus causing
a crash when digest_null is used.

This patch fixes this by also skipping the post-processing when
there is no authentication.

Fixes: 104880a6b470 ("crypto: authencesn - Convert to new AEAD...")
Reported-by: Jan Tluka <jtluka@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 crypto/authencesn.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/crypto/authencesn.c
+++ b/crypto/authencesn.c
@@ -248,6 +248,9 @@ static int crypto_authenc_esn_decrypt_ta
 	u8 *ihash = ohash + crypto_ahash_digestsize(auth);
 	u32 tmp[2];
 
+	if (!authsize)
+		goto decrypt;
+
 	/* Move high-order bits of sequence number back. */
 	scatterwalk_map_and_copy(tmp, dst, 4, 4, 0);
 	scatterwalk_map_and_copy(tmp + 1, dst, assoclen + cryptlen, 4, 0);
@@ -256,6 +259,8 @@ static int crypto_authenc_esn_decrypt_ta
 	if (crypto_memneq(ihash, ohash, authsize))
 		return -EBADMSG;
 
+decrypt:
+
 	sg_init_table(areq_ctx->dst, 2);
 	dst = scatterwalk_ffwd(areq_ctx->dst, dst, assoclen);