[3.16.y-ckt stable] Patch "spi: spidev: fix possible arithmetic overflow for multi-transfer message" has been added to staging queue

[Luis Henriques]

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

    spi: spidev: fix possible arithmetic overflow for multi-transfer message

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-ckt11.

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 a53a7ec98e4943480da76accd2edd12685c78e77 Mon Sep 17 00:00:00 2001
From: Ian Abbott <abbotti at mev.co.uk>
Date: Mon, 23 Mar 2015 17:50:27 +0000
Subject: spi: spidev: fix possible arithmetic overflow for multi-transfer
 message

commit f20fbaad7620af2df36a1f9d1c9ecf48ead5b747 upstream.

`spidev_message()` sums the lengths of the individual SPI transfers to
determine the overall SPI message length.  It restricts the total
length, returning an error if too long, but it does not check for
arithmetic overflow.  For example, if the SPI message consisted of two
transfers and the first has a length of 10 and the second has a length
of (__u32)(-1), the total length would be seen as 9, even though the
second transfer is actually very long.  If the second transfer specifies
a null `rx_buf` and a non-null `tx_buf`, the `copy_from_user()` could
overrun the spidev's pre-allocated tx buffer before it reaches an
invalid user memory address.  Fix it by checking that neither the total
nor the individual transfer lengths exceed the maximum allowed value.

Thanks to Dan Carpenter for reporting the potential integer overflow.

Signed-off-by: Ian Abbott <abbotti at mev.co.uk>
Signed-off-by: Mark Brown <broonie at kernel.org>
[ luis: backported to 3.16: used backport provided by Ian ]
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/spi/spidev.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c
index e3bc23bb5883..621df17214a5 100644
--- a/drivers/spi/spidev.c
+++ b/drivers/spi/spidev.c
@@ -244,7 +244,10 @@ static int spidev_message(struct spidev_data *spidev,
 		k_tmp->len = u_tmp->len;

 		total += k_tmp->len;
-		if (total > bufsiz) {
+		/* Check total length of transfers.  Also check each
+		 * transfer length to avoid arithmetic overflow.
+		 */
+		if (total > bufsiz || k_tmp->len > bufsiz) {
 			status = -EMSGSIZE;
 			goto done;
 		}