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[PATCH] mm/memblock.c: fix NULL dereference error

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Hi Andrew,

this patch is part of https://lkml.org/lkml/2016/7/26/347 and isn't merged in
as you advised in another mail, i release this patch against linus's mainline
for fixing relevant bugs completely, see test patch attached for verification
details

From 5a74cb46b7754a45428ff95f4653ad27025c3131 Mon Sep 17 00:00:00 2001
From: zijun_hu <zijun_hu@htc.com>
Date: Tue, 2 Aug 2016 12:35:28 +0800
Subject: [PATCH] mm/memblock.c: fix NULL dereference error

it causes NULL dereference error and failure to get type_a->regions[0] info
if parameter type_b of __next_mem_range_rev() == NULL

the bugs are fixed by checking before dereferring and initializing idx_b
to 0

the approach is tested by dumping all types of region via __memblock_dump_all()
and __next_mem_range_rev() fixed to UART separately, the result is okay after
checking the logs

Signed-off-by: zijun_hu <zijun_hu@htc.com>
Tested-by: zijun_hu <zijun_hu@htc.com>
Acked-by: Tejun Heo <tj@kernel.org>
---
 mm/memblock.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index ff5ff3b..250dd48 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -994,7 +994,10 @@ void __init_memblock __next_mem_range_rev(u64 *idx, int nid, ulong flags,
 
 	if (*idx == (u64)ULLONG_MAX) {
 		idx_a = type_a->cnt - 1;
-		idx_b = type_b->cnt;
+		if (type_b != NULL)
+			idx_b = type_b->cnt;
+		else
+			idx_b = 0;
 	}
 
 	for (; idx_a >= 0; idx_a--) {
-- 
1.9.1

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[PATCH] mm/memblock.c: fix NULL dereference error zijun_hu <zijun_hu@zoho.com> - 2016-08-02 07:10 +0200
  Re: [PATCH] mm/memblock.c: fix NULL dereference error kbuild test robot <lkp@intel.com> - 2016-08-02 07:30 +0200
    Re: [PATCH] mm/memblock.c: fix NULL dereference error zijun_hu <zijun_hu@zoho.com> - 2016-08-02 07:40 +0200
  Re: [PATCH] mm/memblock.c: fix NULL dereference error zijun_hu <zijun_hu@zoho.com> - 2016-08-02 07:50 +0200
  Re: [PATCH] mm/memblock.c: fix NULL dereference error zijun_hu <zijun_hu@zoho.com> - 2016-08-02 23:20 +0200

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