2020-09-10 02:41:52

by Jing Xiangfeng

Subject: [PATCH] drm/mm: prevent a potential null-pointer dereference

The macro 'DECLARE_NEXT_HOLE_ADDR' may hit a potential null-pointer
dereference. So use 'entry' after checking it.

Fixes: 5fad79fd66ff ("drm/mm: cleanup and improve next_hole_*_addr()")
Signed-off-by: Jing Xiangfeng <[email protected]>
---
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)) \
--
2.17.1

2020-09-10 09:00:34

by Christian König

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

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?

Christian.

>
> Fixes: 5fad79fd66ff ("drm/mm: cleanup and improve next_hole_*_addr()")
> Signed-off-by: Jing Xiangfeng <[email protected]>
> ---
> 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)) \

2020-09-10 12:43:13

by Jing Xiangfeng

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 <[email protected]>
>> ---
>> 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)) \
>
> .
>