FAILED: patch "[PATCH] crypto: algif_skcipher - only call put_page on referenced and" failed to apply to 4.4-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 445a582738de6802669aeed9c33ca406c23c3b1f Mon Sep 17 00:00:00 2001
From: Stephan Mueller <smueller@chronox.de>
Date: Wed, 16 Aug 2017 11:56:24 +0200
Subject: [PATCH] crypto: algif_skcipher - only call put_page on referenced and
 used pages

For asynchronous operation, SGs are allocated without a page mapped to
them or with a page that is not used (ref-counted). If the SGL is freed,
the code must only call put_page for an SG if there was a page assigned
and ref-counted in the first place.

This fixes a kernel crash when using io_submit with more than one iocb
using the sendmsg and sendpage (vmsplice/splice) interface.

Cc: <stable@vger.kernel.org>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

diff --git a/crypto/algif_skcipher.c b/crypto/algif_skcipher.c
index 43839b00fe6c..903605dbc1a5 100644
--- a/crypto/algif_skcipher.c
+++ b/crypto/algif_skcipher.c
@@ -87,8 +87,13 @@ static void skcipher_free_async_sgls(struct skcipher_async_req *sreq)
 	}
 	sgl = sreq->tsg;
 	n = sg_nents(sgl);
-	for_each_sg(sgl, sg, n, i)
-		put_page(sg_page(sg));
+	for_each_sg(sgl, sg, n, i) {
+		struct page *page = sg_page(sg);
+
+		/* some SGs may not have a page mapped */
+		if (page && page_ref_count(page))
+			put_page(page);
+	}
 
 	kfree(sreq->tsg);
 }