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

[Alex Vesker <valex@mellanox.com>]

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...