linux-kernel - Re: [PATCH] drm/mm: prevent a potential null-pointer dereference

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Message-ID: <5F5A1D80.2060902@huawei.com>
Date:   Thu, 10 Sep 2020 20:35:12 +0800
From:   Jing Xiangfeng <jingxiangfeng@...wei.com>
To:     Christian König <christian.koenig@....com>,
        <maarten.lankhorst@...ux.intel.com>, <mripard@...nel.org>,
        <tzimmermann@...e.de>, <airlied@...ux.ie>, <daniel@...ll.ch>,
        <nirmoy.das@....com>
CC:     <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/mm: prevent a potential null-pointer dereference



On 2020/9/10 16:58, Christian König wrote:
> Am 10.09.20 um 04:38 schrieb Jing Xiangfeng:
>> The macro 'DECLARE_NEXT_HOLE_ADDR' may hit a potential null-pointer
>> dereference. So use 'entry' after checking it.
>
> I don't see a potential null-pointer dereference here.
>
> Where should that be?

In current code，the "entry" pointer is checked after entry->rb_hole_addr.
	Thanks
>
> Christian.
>
>>
>> Fixes: 5fad79fd66ff ("drm/mm: cleanup and improve next_hole_*_addr()")
>> Signed-off-by: Jing Xiangfeng <jingxiangfeng@...wei.com>
>> ---
>>   drivers/gpu/drm/drm_mm.c | 7 +++++--
>>   1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
>> index a4a04d246135..6fcf70f71962 100644
>> --- a/drivers/gpu/drm/drm_mm.c
>> +++ b/drivers/gpu/drm/drm_mm.c
>> @@ -392,11 +392,14 @@ first_hole(struct drm_mm *mm,
>>   #define DECLARE_NEXT_HOLE_ADDR(name, first, last)            \
>>   static struct drm_mm_node *name(struct drm_mm_node *entry, u64
>> size)    \
>>   {                                    \
>> -    struct rb_node *parent, *node = &entry->rb_hole_addr;        \
>> +    struct rb_node *parent, *node;                    \
>>                                       \
>> -    if (!entry || RB_EMPTY_NODE(node))                \
>> +    if (!entry)                            \
>>           return NULL;                        \
>>                                       \
>> +    node = &entry->rb_hole_addr;                    \
>> +    if (RB_EMPTY_NODE(node))                    \
>> +        return NULL;                        \
>>       if (usable_hole_addr(node->first, size)) {            \
>>           node = node->first;                    \
>>           while (usable_hole_addr(node->last, size))        \
>
> .
>