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

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