[PATCH 3.2 031/185] PM / hibernate: Avoid overflow inhibernate_preallocate_memory()

[Ben Hutchings]

3.2.54-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Aaron Lu <aaron.lu@xxxxxxxxx>

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@xxxxx>
Signed-off-by: Aaron Lu <aaron.lu@xxxxxxxxx>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 kernel/power/snapshot.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -1390,7 +1390,11 @@ 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. */

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