From 0cabf2af6f5ac3c88cb106c4e06087a5a39b8e1e Mon Sep 17 00:00:00 2001
From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Sat, 7 Oct 2017 11:29:48 +0800
Subject: [PATCH] crypto: skcipher - Fix crash on zero-length input
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Git-commit: 0cabf2af6f5ac3c88cb106c4e06087a5a39b8e1e
Patch-mainline: v4.14-rc5
References: bsc#1051510

The skcipher walk interface doesn't handle zero-length input
properly as the old blkcipher walk interface did.  This is due
to the fact that the length check is done too late.

This patch moves the length check forward so that it does the
right thing.

Fixes: b286d8b1a690 ("crypto: skcipher - Add skcipher walk...")
Cc: <stable@vger.kernel.org>
Reported-by: Stephan Müller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 crypto/skcipher.c |   17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

--- a/crypto/skcipher.c
+++ b/crypto/skcipher.c
@@ -426,14 +426,9 @@ static int skcipher_copy_iv(struct skcip
 
 static int skcipher_walk_first(struct skcipher_walk *walk)
 {
-	walk->nbytes = 0;
-
 	if (WARN_ON_ONCE(in_irq()))
 		return -EDEADLK;
 
-	if (unlikely(!walk->total))
-		return 0;
-
 	walk->buffer = NULL;
 	if (unlikely(((unsigned long)walk->iv & walk->alignmask))) {
 		int err = skcipher_copy_iv(walk);
@@ -452,10 +447,15 @@ static int skcipher_walk_skcipher(struct
 {
 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 
+	walk->total = req->cryptlen;
+	walk->nbytes = 0;
+
+	if (unlikely(!walk->total))
+		return 0;
+
 	scatterwalk_start(&walk->in, req->src);
 	scatterwalk_start(&walk->out, req->dst);
 
-	walk->total = req->cryptlen;
 	walk->iv = req->iv;
 	walk->oiv = req->iv;
 
@@ -509,6 +509,11 @@ static int skcipher_walk_aead_common(str
 	struct crypto_aead *tfm = crypto_aead_reqtfm(req);
 	int err;
 
+	walk->nbytes = 0;
+
+	if (unlikely(!walk->total))
+		return 0;
+
 	walk->flags &= ~SKCIPHER_WALK_PHYS;
 
 	scatterwalk_start(&walk->in, req->src);