[3.16.y-ckt stable] Patch "sg_start_req(): make sure that there's not too many elements in iovec" has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    sg_start_req(): make sure that there's not too many elements in iovec

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt16.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 2558b5b7ab218804ee03f5f13c0d3036e409dabe Mon Sep 17 00:00:00 2001
From: Al Viro <viro at zeniv.linux.org.uk>
Date: Sat, 1 Aug 2015 18:25:59 +0100
Subject: sg_start_req(): make sure that there's not too many elements in iovec

commit 451a2886b6bf90e2fb378f7c46c655450fb96e81 upstream.

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)
Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
[bwh: s/MAX_UIOVEC/UIO_MAXIOV/. This was fixed upstream by commit
 fdc81f45e9f5 ("sg_start_req(): use import_iovec()"), but we don't have
 that function.]
Signed-off-by: Ben Hutchings <ben at decadent.org.uk>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/scsi/sg.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index 791460b798f4..2aa95c89b5bf 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1693,6 +1693,9 @@ static int sg_start_req(Sg_request *srp, unsigned char *cmd)
 			md->from_user = 0;
 	}

+	if (unlikely(iov_count > UIO_MAXIOV))
+		return -EINVAL;
+
 	if (iov_count) {
 		int len, size = sizeof(struct sg_iovec) * iov_count;
 		struct iovec *iov;