Commit 8139ad04 authored by Andrey Ryabinin's avatar Andrey Ryabinin Committed by Linus Torvalds

mm/page_alloc.c: avoid potential NULL pointer dereference

ac.preferred_zoneref->zone passed to alloc_flags_nofragment() can be NULL.
'zone' pointer unconditionally derefernced in alloc_flags_nofragment().
Bail out on NULL zone to avoid potential crash.  Currently we don't see
any crashes only because alloc_flags_nofragment() has another bug which
allows compiler to optimize away all accesses to 'zone'.

Link: http://lkml.kernel.org/r/20190423120806.3503-1-aryabinin@virtuozzo.com
Fixes: 6bb15450 ("mm, page_alloc: spread allocations across zones before introducing fragmentation")
Signed-off-by: default avatarAndrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: default avatarMel Gorman <mgorman@techsingularity.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ee8ab0ee
...@@ -3432,6 +3432,9 @@ alloc_flags_nofragment(struct zone *zone, gfp_t gfp_mask) ...@@ -3432,6 +3432,9 @@ alloc_flags_nofragment(struct zone *zone, gfp_t gfp_mask)
alloc_flags |= ALLOC_KSWAPD; alloc_flags |= ALLOC_KSWAPD;
#ifdef CONFIG_ZONE_DMA32 #ifdef CONFIG_ZONE_DMA32
if (!zone)
return alloc_flags;
if (zone_idx(zone) != ZONE_NORMAL) if (zone_idx(zone) != ZONE_NORMAL)
goto out; goto out;
......
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