FAILED: patch "[PATCH] sg_start_req(): make sure that there's not too many elements" failed to apply to 4.0-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.0-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 451a2886b6bf90e2fb378f7c46c655450fb96e81 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Sat, 21 Mar 2015 20:08:18 -0400
Subject: [PATCH] sg_start_req(): make sure that there's not too many elements
 in iovec

unfortunately, allowing an arbitrary 16bit value means a possibility of
overflow in the calculation of total number of pages in bio_map_user_iov() -
we rely on there being no more than PAGE_SIZE members of sum in the
first loop there.  If that sum wraps around, we end up allocating
too small array of pointers to pages and it's easy to overflow it in
the second loop.

X-Coverup: TINC (and there's no lumber cartel either)
Cc: stable@vger.kernel.org # way, way back
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index d383f84869aa..b5a4db883223 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1744,6 +1744,9 @@ sg_start_req(Sg_request *srp, unsigned char *cmd)
 			md->from_user = 0;
 	}
 
+	if (unlikely(iov_count > MAX_UIOVEC))
+		return -EINVAL;
+
 	if (iov_count) {
 		int size = sizeof(struct iovec) * iov_count;
 		struct iovec *iov;