[3.8.y.z extended stable] Patch "PM / hibernate: Avoid overflow in hibernate_preallocate_memory()" has been added to staging queue

[Kamal Mostafa]

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

    PM / hibernate: Avoid overflow in hibernate_preallocate_memory()

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.14.

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

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From bcf15093aae3434de56d49f41e5c2bf1fe8e668c Mon Sep 17 00:00:00 2001
From: Aaron Lu <aaron.lu at intel.com>
Date: Wed, 6 Nov 2013 08:41:31 +0800
Subject: PM / hibernate: Avoid overflow in hibernate_preallocate_memory()

commit fd432b9f8c7c88428a4635b9f5a9c6e174df6e36 upstream.

When system has a lot of highmem (e.g. 16GiB using a 32 bits kernel),
the code to calculate how much memory we need to preallocate in
normal zone may cause overflow. As Leon has analysed:

 It looks that during computing 'alloc' variable there is overflow:
 alloc = (3943404 - 1970542) - 1978280 = -5418 (signed)
 And this function goes to err_out.

Fix this by avoiding that overflow.

References: https://bugzilla.kernel.org/show_bug.cgi?id=60817
Reported-and-tested-by: Leon Drugi <eyak at wp.pl>
Signed-off-by: Aaron Lu <aaron.lu at intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 kernel/power/snapshot.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index 0de2857..91c04f1 100644
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -1398,7 +1398,11 @@ int hibernate_preallocate_memory(void)
 	 * highmem and non-highmem zones separately.
 	 */
 	pages_highmem = preallocate_image_highmem(highmem / 2);
-	alloc = (count - max_size) - pages_highmem;
+	alloc = count - max_size;
+	if (alloc > pages_highmem)
+		alloc -= pages_highmem;
+	else
+		alloc = 0;
 	pages = preallocate_image_memory(alloc, avail_normal);
 	if (pages < alloc) {
 		/* We have exhausted non-highmem pages, try highmem. */
--
1.8.3.2