PM / hibernate: Avoid overflow in hibernate_preallocate_memory()

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@wp.pl>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
index 98c3b34a4cffcedeae812de0ddc947f874cef839..10c22cae83a035e43eb54a79272fd1e6ae2fc757 100644 (file)
--- a/kernel/power/snapshot.c
+++ b/kernel/power/snapshot.c
@@ -1402,7 +1402,11 @@ 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. */