[PATCH] net: mellanox: prevent resource leak on htbl

[PATCH] net: mellanox: prevent resource leak on htbl

[Cengiz Can]

According to a Coverity static analysis tool,
`drivers/net/mellanox/mlx5/core/steering/dr_rule.c#63` leaks a
`struct mlx5dr_ste_htbl *` named `new_htbl` while returning from
`dr_rule_create_collision_htbl` function.

A annotated snippet of the possible resource leak follows:

```
static struct mlx5dr_ste *
dr_rule_create_collision_htbl(struct mlx5dr_matcher *matcher,
                              struct mlx5dr_matcher_rx_tx *nic_matcher,
                              u8 *hw_ste)
   /* ... */
   /* ... */

   /* Storage is returned from allocation function mlx5dr_ste_htbl_alloc. */
   /* Assigning: new_htbl = storage returned from mlx5dr_ste_htbl_alloc(..) */
        new_htbl = mlx5dr_ste_htbl_alloc(dmn->ste_icm_pool,
                                         DR_CHUNK_SIZE_1,
                                         MLX5DR_STE_LU_TYPE_DONT_CARE,
                                         0);
   /* Condition !new_htbl, taking false branch. */
        if (!new_htbl) {
                mlx5dr_dbg(dmn, "Failed allocating collision table\n");
                return NULL;
        }

        /* One and only entry, never grows */
        ste = new_htbl->ste_arr;
        mlx5dr_ste_set_miss_addr(hw_ste, nic_matcher->e_anchor->chunk->icm_addr);
   /* Resource new_htbl is not freed or pointed-to in mlx5dr_htbl_get */
        mlx5dr_htbl_get(new_htbl);

   /* Variable new_htbl going out of scope leaks the storage it points to. */
        return ste;
```

There's a caller of this function which does refcounting and free'ing by
itself but that function also skips free'ing `new_htbl` due to missing
jump to error label. (referring to `dr_rule_create_collision_entry lines
75-77. They don't jump to `free_tbl`)

Added a `kfree(new_htbl)` just before returning `ste` pointer to fix the
leak.

Signed-off-by: Cengiz Can <cengiz@kernel.wtf>
---

This might be totally breaking the refcounting logic in the file so
please provide any feedback so I can evolve this into something more
suitable.

For the record, Coverity scan id is CID 1457773.

 drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c b/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c
index e4cff7abb348..047b403c61db 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c
@@ -60,6 +60,8 @@ dr_rule_create_collision_htbl(struct mlx5dr_matcher *matcher,
 	mlx5dr_ste_set_miss_addr(hw_ste, nic_matcher->e_anchor->chunk->icm_addr);
 	mlx5dr_htbl_get(new_htbl);

+	kfree(new_htbl);
+
 	return ste;
 }

--
2.24.1

Re: [PATCH] net: mellanox: prevent resource leak on htbl

[Alex Vesker]

On 1/13/2020 3:46 PM, Cengiz Can wrote:
> According to a Coverity static analysis tool,
> `drivers/net/mellanox/mlx5/core/steering/dr_rule.c#63` leaks a
> `struct mlx5dr_ste_htbl *` named `new_htbl` while returning from
> `dr_rule_create_collision_htbl` function.
>
> A annotated snippet of the possible resource leak follows:
>
> ```
> static struct mlx5dr_ste *
> dr_rule_create_collision_htbl(struct mlx5dr_matcher *matcher,
>                               struct mlx5dr_matcher_rx_tx *nic_matcher,
>                               u8 *hw_ste)
>    /* ... */
>    /* ... */
>
>    /* Storage is returned from allocation function mlx5dr_ste_htbl_alloc. */
>    /* Assigning: new_htbl = storage returned from mlx5dr_ste_htbl_alloc(..) */
>         new_htbl = mlx5dr_ste_htbl_alloc(dmn->ste_icm_pool,
>                                          DR_CHUNK_SIZE_1,
>                                          MLX5DR_STE_LU_TYPE_DONT_CARE,
>                                          0);
>    /* Condition !new_htbl, taking false branch. */
>         if (!new_htbl) {
>                 mlx5dr_dbg(dmn, "Failed allocating collision table\n");
>                 return NULL;
>         }
>
>         /* One and only entry, never grows */
>         ste = new_htbl->ste_arr;
>         mlx5dr_ste_set_miss_addr(hw_ste, nic_matcher->e_anchor->chunk->icm_addr);
>    /* Resource new_htbl is not freed or pointed-to in mlx5dr_htbl_get */
>         mlx5dr_htbl_get(new_htbl);
>
>    /* Variable new_htbl going out of scope leaks the storage it points to. */
>         return ste;
> ```
>
> There's a caller of this function which does refcounting and free'ing by
> itself but that function also skips free'ing `new_htbl` due to missing
> jump to error label. (referring to `dr_rule_create_collision_entry lines
> 75-77. They don't jump to `free_tbl`)
>
> Added a `kfree(new_htbl)` just before returning `ste` pointer to fix the
> leak.
>
> Signed-off-by: Cengiz Can <cengiz@kernel.wtf>
> ---
>
> This might be totally breaking the refcounting logic in the file so
> please provide any feedback so I can evolve this into something more
> suitable.
>
> For the record, Coverity scan id is CID 1457773.
>
>  drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c b/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c
> index e4cff7abb348..047b403c61db 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c
> @@ -60,6 +60,8 @@ dr_rule_create_collision_htbl(struct mlx5dr_matcher *matcher,
>  	mlx5dr_ste_set_miss_addr(hw_ste, nic_matcher->e_anchor->chunk->icm_addr);
>  	mlx5dr_htbl_get(new_htbl);
>
> +	kfree(new_htbl);
> +
>  	return ste;
>  }
>
> --
> 2.24.1
>
>
The fix looks incorrect to me.
The table is pointed by each ste in the ste_arr, ste->new_htbl and being
freed on mlx5dr_htbl_put.
We tested kmemleak a few days ago and came clean.
usually coverity is not wrong, but in this case I don't see the bug...

Re: [PATCH] net: mellanox: prevent resource leak on htbl

[Cengiz Can]

On 2020-01-13 17:49, Alex Vesker wrote:
> On 1/13/2020 3:46 PM, Cengiz Can wrote:
>> According to a Coverity static analysis tool,
>> `drivers/net/mellanox/mlx5/core/steering/dr_rule.c#63` leaks a
>> `struct mlx5dr_ste_htbl *` named `new_htbl` while returning from
>> `dr_rule_create_collision_htbl` function.
>> 
>> A annotated snippet of the possible resource leak follows:
>> 
>> ```
>> static struct mlx5dr_ste *
>> dr_rule_create_collision_htbl(struct mlx5dr_matcher *matcher,
>>                               struct mlx5dr_matcher_rx_tx 
>> *nic_matcher,
>>                               u8 *hw_ste)
>>    /* ... */
>>    /* ... */
>> 
>>    /* Storage is returned from allocation function 
>> mlx5dr_ste_htbl_alloc. */
>>    /* Assigning: new_htbl = storage returned from 
>> mlx5dr_ste_htbl_alloc(..) */
>>         new_htbl = mlx5dr_ste_htbl_alloc(dmn->ste_icm_pool,
>>                                          DR_CHUNK_SIZE_1,
>>                                          MLX5DR_STE_LU_TYPE_DONT_CARE,
>>                                          0);
>>    /* Condition !new_htbl, taking false branch. */
>>         if (!new_htbl) {
>>                 mlx5dr_dbg(dmn, "Failed allocating collision 
>> table\n");
>>                 return NULL;
>>         }
>> 
>>         /* One and only entry, never grows */
>>         ste = new_htbl->ste_arr;
>>         mlx5dr_ste_set_miss_addr(hw_ste, 
>> nic_matcher->e_anchor->chunk->icm_addr);
>>    /* Resource new_htbl is not freed or pointed-to in mlx5dr_htbl_get 
>> */
>>         mlx5dr_htbl_get(new_htbl);
>> 
>>    /* Variable new_htbl going out of scope leaks the storage it points 
>> to. */
>>         return ste;
>> ```
>> 
>> There's a caller of this function which does refcounting and free'ing 
>> by
>> itself but that function also skips free'ing `new_htbl` due to missing
>> jump to error label. (referring to `dr_rule_create_collision_entry 
>> lines
>> 75-77. They don't jump to `free_tbl`)
>> 
>> Added a `kfree(new_htbl)` just before returning `ste` pointer to fix 
>> the
>> leak.
>> 
>> Signed-off-by: Cengiz Can <cengiz@kernel.wtf>
>> ---
>> 
>> This might be totally breaking the refcounting logic in the file so
>> please provide any feedback so I can evolve this into something more
>> suitable.
>> 
>> For the record, Coverity scan id is CID 1457773.
>> 
>>  drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c | 2 ++
>>  1 file changed, 2 insertions(+)
>> 
>> diff --git 
>> a/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c 
>> b/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c
>> index e4cff7abb348..047b403c61db 100644
>> --- a/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c
>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/steering/dr_rule.c
>> @@ -60,6 +60,8 @@ dr_rule_create_collision_htbl(struct mlx5dr_matcher 
>> *matcher,
>>  	mlx5dr_ste_set_miss_addr(hw_ste, 
>> nic_matcher->e_anchor->chunk->icm_addr);
>>  	mlx5dr_htbl_get(new_htbl);
>> 
>> +	kfree(new_htbl);
>> +
>>  	return ste;
>>  }
>> 
>> --
>> 2.24.1
>> 
>> 
> The fix looks incorrect to me.
> The table is pointed by each ste in the ste_arr, ste->new_htbl and 
> being
> freed on mlx5dr_htbl_put.
> We tested kmemleak a few days ago and came clean.
> usually coverity is not wrong, but in this case I don't see the bug...

Hello Alex,

To my experience, the refcounting logic is complex and spread out to 
multiple files.

It might be a false positive on Coverity's side.

If it certainly sounds wrong, we can ignore this.

Thanks

-- 
Cengiz Can
@cengiz_io