Commit 8139ad04 authored Apr 25, 2019 by Andrey Ryabinin Committed by Linus Torvalds Apr 26, 2019

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: Andrey Ryabinin <aryabinin@virtuozzo.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent ee8ab0ee

mm/page_alloc.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -3432,6 +3432,9 @@ alloc_flags_nofragment(struct zone *zone, gfp_t gfp_mask)
		alloc_flags \|= ALLOC_KSWAPD;

		#ifdef CONFIG_ZONE_DMA32
		if (!zone)
		return alloc_flags;

		if (zone_idx(zone) != ZONE_NORMAL)
		goto out;

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