Patch "crypto: shash - Fix zero-length shash ahash digest crash" has been added to the 4.13-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    crypto: shash - Fix zero-length shash ahash digest crash

to the 4.13-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     crypto-shash-fix-zero-length-shash-ahash-digest-crash.patch
and it can be found in the queue-4.13 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From b61907bb42409adf9b3120f741af7c57dd7e3db2 Mon Sep 17 00:00:00 2001
From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Mon, 9 Oct 2017 23:30:02 +0800
Subject: crypto: shash - Fix zero-length shash ahash digest crash
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

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

commit b61907bb42409adf9b3120f741af7c57dd7e3db2 upstream.

The shash ahash digest adaptor function may crash if given a
zero-length input together with a null SG list.  This is because
it tries to read the SG list before looking at the length.

This patch fixes it by checking the length first.

Reported-by: Stephan Müller<smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Tested-by: Stephan Müller <smueller@chronox.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 crypto/shash.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/crypto/shash.c
+++ b/crypto/shash.c
@@ -275,12 +275,14 @@ static int shash_async_finup(struct ahas
 
 int shash_ahash_digest(struct ahash_request *req, struct shash_desc *desc)
 {
-	struct scatterlist *sg = req->src;
-	unsigned int offset = sg->offset;
 	unsigned int nbytes = req->nbytes;
+	struct scatterlist *sg;
+	unsigned int offset;
 	int err;
 
-	if (nbytes < min(sg->length, ((unsigned int)(PAGE_SIZE)) - offset)) {
+	if (nbytes &&
+	    (sg = req->src, offset = sg->offset,
+	     nbytes < min(sg->length, ((unsigned int)(PAGE_SIZE)) - offset))) {
 		void *data;
 
 		data = kmap_atomic(sg_page(sg));


Patches currently in stable-queue which might be from herbert@gondor.apana.org.au are

queue-4.13/crypto-skcipher-fix-crash-on-zero-length-input.patch
queue-4.13/crypto-shash-fix-zero-length-shash-ahash-digest-crash.patch