[PATCH] maple_tree: Fix potential out-of-bounds access in mas_wr_end_piv()

[PATCH] maple_tree: Fix potential out-of-bounds access in mas_wr_end_piv()

[Peng Zhang]

Access to the pivots array may be out of bounds. Fix it by changing the
code to ensure that the index of the pivots does not go out of bounds.
It is difficult to assess user-visible impact.

Fixes: 54a611b60590 ("Maple Tree: add new data structure")
Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
---
 lib/maple_tree.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 110a36479dced..5a49327444d76 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -4263,11 +4263,13 @@ static inline bool mas_wr_slot_store(struct ma_wr_state *wr_mas)
 
 static inline void mas_wr_end_piv(struct ma_wr_state *wr_mas)
 {
-	while ((wr_mas->mas->last > wr_mas->end_piv) &&
-	       (wr_mas->offset_end < wr_mas->node_end))
-		wr_mas->end_piv = wr_mas->pivots[++wr_mas->offset_end];
+	while ((wr_mas->offset_end < wr_mas->node_end) &&
+	       (wr_mas->mas->last > wr_mas->pivots[wr_mas->offset_end]))
+		wr_mas->offset_end++;
 
-	if (wr_mas->mas->last > wr_mas->end_piv)
+	if (wr_mas->offset_end < wr_mas->node_end)
+		wr_mas->end_piv = wr_mas->pivots[wr_mas->offset_end];
+	else
 		wr_mas->end_piv = wr_mas->mas->max;
 }
 
@@ -4424,7 +4426,6 @@ static inline void *mas_wr_store_entry(struct ma_wr_state *wr_mas)
 	}
 
 	/* At this point, we are at the leaf node that needs to be altered. */
-	wr_mas->end_piv = wr_mas->r_max;
 	mas_wr_end_piv(wr_mas);
 
 	if (!wr_mas->entry)
-- 
2.20.1

Re: [PATCH] maple_tree: Fix potential out-of-bounds access in mas_wr_end_piv()

[Liam R. Howlett]

* Peng Zhang <zhangpeng.00@bytedance.com> [230503 23:14]:
> Access to the pivots array may be out of bounds. Fix it by changing the
> code to ensure that the index of the pivots does not go out of bounds.
> It is difficult to assess user-visible impact.

This is indeed an issue.  There isn't any user-visible impact for
current node types, since the overflow will access the slots and be
corrected in the next if clause, but it's certainly better to fix this.

The commit message is also not as descriptive as necessary, perhaps
something like:

Check the write offset end bounds before using it as the offset into the
pivot array.  This avoids a possible out-of-bounds access on the pivot
array if the write extends to the last slot in the node, in which case
the node maximum should be used as the end pivot.

Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>

> 
> Fixes: 54a611b60590 ("Maple Tree: add new data structure")

Cc stable ?

> Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
> ---
>  lib/maple_tree.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
> index 110a36479dced..5a49327444d76 100644
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -4263,11 +4263,13 @@ static inline bool mas_wr_slot_store(struct ma_wr_state *wr_mas)
>  
>  static inline void mas_wr_end_piv(struct ma_wr_state *wr_mas)
>  {
> -	while ((wr_mas->mas->last > wr_mas->end_piv) &&
> -	       (wr_mas->offset_end < wr_mas->node_end))
> -		wr_mas->end_piv = wr_mas->pivots[++wr_mas->offset_end];
> +	while ((wr_mas->offset_end < wr_mas->node_end) &&
> +	       (wr_mas->mas->last > wr_mas->pivots[wr_mas->offset_end]))
> +		wr_mas->offset_end++;
>  
> -	if (wr_mas->mas->last > wr_mas->end_piv)
> +	if (wr_mas->offset_end < wr_mas->node_end)
> +		wr_mas->end_piv = wr_mas->pivots[wr_mas->offset_end];
> +	else
>  		wr_mas->end_piv = wr_mas->mas->max;
>  }
>  
> @@ -4424,7 +4426,6 @@ static inline void *mas_wr_store_entry(struct ma_wr_state *wr_mas)
>  	}
>  
>  	/* At this point, we are at the leaf node that needs to be altered. */
> -	wr_mas->end_piv = wr_mas->r_max;
>  	mas_wr_end_piv(wr_mas);
>  
>  	if (!wr_mas->entry)
> -- 
> 2.20.1
> 

Re: [PATCH] maple_tree: Fix potential out-of-bounds access in mas_wr_end_piv()

[Peng Zhang]

在 2023/5/6 09:14, Liam R. Howlett 写道:
> * Peng Zhang <zhangpeng.00@bytedance.com> [230503 23:14]:
>> Access to the pivots array may be out of bounds. Fix it by changing the
>> code to ensure that the index of the pivots does not go out of bounds.
>> It is difficult to assess user-visible impact.
> 
> This is indeed an issue.  There isn't any user-visible impact for
> current node types, since the overflow will access the slots and be
> corrected in the next if clause, but it's certainly better to fix this.
> 
> The commit message is also not as descriptive as necessary, perhaps
> something like:
> 
> Check the write offset end bounds before using it as the offset into the
> pivot array.  This avoids a possible out-of-bounds access on the pivot
> array if the write extends to the last slot in the node, in which case
> the node maximum should be used as the end pivot.
> 
> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com>
> 
>>
>> Fixes: 54a611b60590 ("Maple Tree: add new data structure")
> 
> Cc stable ?
I don't know if it should be cc stable since Andrew says it
always needs to describe user-visible impact.
> 
>> Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
>> ---
>>   lib/maple_tree.c | 11 ++++++-----
>>   1 file changed, 6 insertions(+), 5 deletions(-)
>>
>> diff --git a/lib/maple_tree.c b/lib/maple_tree.c
>> index 110a36479dced..5a49327444d76 100644
>> --- a/lib/maple_tree.c
>> +++ b/lib/maple_tree.c
>> @@ -4263,11 +4263,13 @@ static inline bool mas_wr_slot_store(struct ma_wr_state *wr_mas)
>>   
>>   static inline void mas_wr_end_piv(struct ma_wr_state *wr_mas)
>>   {
>> -	while ((wr_mas->mas->last > wr_mas->end_piv) &&
>> -	       (wr_mas->offset_end < wr_mas->node_end))
>> -		wr_mas->end_piv = wr_mas->pivots[++wr_mas->offset_end];
>> +	while ((wr_mas->offset_end < wr_mas->node_end) &&
>> +	       (wr_mas->mas->last > wr_mas->pivots[wr_mas->offset_end]))
>> +		wr_mas->offset_end++;
>>   
>> -	if (wr_mas->mas->last > wr_mas->end_piv)
>> +	if (wr_mas->offset_end < wr_mas->node_end)
>> +		wr_mas->end_piv = wr_mas->pivots[wr_mas->offset_end];
>> +	else
>>   		wr_mas->end_piv = wr_mas->mas->max;
>>   }
>>   
>> @@ -4424,7 +4426,6 @@ static inline void *mas_wr_store_entry(struct ma_wr_state *wr_mas)
>>   	}
>>   
>>   	/* At this point, we are at the leaf node that needs to be altered. */
>> -	wr_mas->end_piv = wr_mas->r_max;
>>   	mas_wr_end_piv(wr_mas);
>>   
>>   	if (!wr_mas->entry)
>> -- 
>> 2.20.1
>>

Re: [PATCH] maple_tree: Fix potential out-of-bounds access in mas_wr_end_piv()

[Andrew Morton]

On Sat, 6 May 2023 09:48:19 +0800 Peng Zhang <perlyzhang@gmail.com> wrote:

> >> Fixes: 54a611b60590 ("Maple Tree: add new data structure")
> > 
> > Cc stable ?
> I don't know if it should be cc stable since Andrew says it
> always needs to describe user-visible impact.

I suppose we may as well backport it - there may be new users of maple
tree which *do* trigger this, and anyone who who tries to backport
those users into earlier kernels will get a nasty surprise.

So I'll add cc:stable to v3, but I won't queue it as a hotfix, so it's
well tested before we propose the backport.