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

[zijun_hu]

On 08/02/2016 01:03 PM, zijun_hu wrote:
> 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@xxxxxxx>
> 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@xxxxxxx>
> Tested-by: zijun_hu <zijun_hu@xxxxxxx>
> Acked-by: Tejun Heo <tj@xxxxxxxxxx>
> ---
>  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--) {
>