Re: [PATCH v2] nvmem: core: fix possibly memleak when use nvmem_cell_info_to_nvmem_cell()

Srinivas Kandagatla
2020-09-23T14:47:23Z

On 23/09/2020 15:13, Vadym Kochan wrote:
> On Wed, Sep 23, 2020 at 03:10:36PM +0100, Srinivas Kandagatla wrote:
>>
>>
>> On 23/09/2020 14:53, Vadym Kochan wrote:
>>> Fix missing 'kfree_const(cell->name)' when call to
>>> nvmem_cell_info_to_nvmem_cell() in several places:
>>>
>>> * after nvmem_cell_info_to_nvmem_cell() failed during
>>> nvmem_add_cells()
>>>
>>> * during nvmem_device_cell_{read,write}. This is fixed by simply
>>> re-using info->name instead of duplicating it:
>>>
>>> cell->name = info->name
>>>
>>> Because cell->name is not used except for error message printing in case
>>> of un-aligned access, the new __nvmem_cell_info_to_nvmem_cell() helper
>>> was introduced.
>>>
>>> Fixes: e2a5402ec7c6 ("nvmem: Add nvmem_device based consumer apis.")
>>> Signed-off-by: Vadym Kochan <vadym.kochan@plvision.eu>
>>> ---
>>> v2:
>>> * remove not needed 'kfree_const(cell->name)' after nvmem_cell_info_to_nvmem_cell()
>>> failed.
>>>
>>> drivers/nvmem/core.c | 35 ++++++++++++++++++++++++++---------
>>> 1 file changed, 26 insertions(+), 9 deletions(-)
>>
>>
>>
>> Really :-)
>>
> But what about nvmem_device_cell_{read,write} case ?
> In my understanding the cell is allocated on the stack but kstrdup() is
You are right!

That is the second issue where the caller outside would fail after
successful call to nvmem_cell_info_to_nvmem_cell() .

Probably we cam free it in failure cases!
something like:

------------------------>cut<---------------------------
diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
index 6cd3edb2eaf6..fb1e756adcee 100644
--- a/drivers/nvmem/core.c
+++ b/drivers/nvmem/core.c
@@ -383,6 +383,7 @@ static int nvmem_cell_info_to_nvmem_cell(struct
nvmem_device *nvmem,
dev_err(&nvmem->dev,
"cell %s unaligned to nvmem stride %d\n",
cell->name, nvmem->stride);
+ kfree_const(cell->name);
return -EINVAL;
}

@@ -1465,8 +1466,10 @@ ssize_t nvmem_device_cell_read(struct
nvmem_device *nvmem,
return rc;

rc = __nvmem_cell_read(nvmem, &cell, buf, &len);
- if (rc)
+ if (rc) {
+ kfree_const(cell->name);
return rc;
+ }

return len;
}
@@ -1494,7 +1497,11 @@ int nvmem_device_cell_write(struct nvmem_device
*nvmem,
if (rc)
return rc;

- return nvmem_cell_write(&cell, buf, cell.bytes);
+ rc = nvmem_cell_write(&cell, buf, cell.bytes);
+ if (rc)
+ kfree_const(cell->name);
+
+ return rc;
}
EXPORT_SYMBOL_GPL(nvmem_device_cell_write);
------------------------>cut<---------------------------

--srini

> not freed in the end, or I missed something ?
>
>>
>> Below change should just fix this the reported issue!
>> ------------------------>cut<---------------------------
>>
>> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
>> index 6cd3edb2eaf6..9fb9112fe75d 100644
>> --- a/drivers/nvmem/core.c
>> +++ b/drivers/nvmem/core.c
>> @@ -383,6 +383,7 @@ static int nvmem_cell_info_to_nvmem_cell(struct
>> nvmem_device *nvmem,
>> dev_err(&nvmem->dev,
>> "cell %s unaligned to nvmem stride %d\n",
>> cell->name, nvmem->stride);
>> + kfree_const(cell->name);
>> return -EINVAL;
>> }
>>
>> ------------------------>cut<---------------------------
>>
>> I don't see a point in the way your patch try to fix this!!
>>
>>
>> --srini
>>
>>>
>>> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
>>> index 6cd3edb2eaf6..e6d1bc414faf 100644
>>> --- a/drivers/nvmem/core.c
>>> +++ b/drivers/nvmem/core.c
>>> @@ -361,16 +361,15 @@ static void nvmem_cell_add(struct nvmem_cell *cell)
>>> blocking_notifier_call_chain(&nvmem_notifier, NVMEM_CELL_ADD, cell);
>>> }
>>> -static int nvmem_cell_info_to_nvmem_cell(struct nvmem_device *nvmem,
>>> - const struct nvmem_cell_info *info,
>>> - struct nvmem_cell *cell)
>>> +static int
>>> +__nvmem_cell_info_to_nvmem_cell(struct nvmem_device *nvmem,
>>> + const struct nvmem_cell_info *info,
>>> + struct nvmem_cell *cell)
>>> {
>>> cell->nvmem = nvmem;
>>> cell->offset = info->offset;
>>> cell->bytes = info->bytes;
>>> - cell->name = kstrdup_const(info->name, GFP_KERNEL);
>>> - if (!cell->name)
>>> - return -ENOMEM;
>>> + cell->name = info->name;
>>> cell->bit_offset = info->bit_offset;
>>> cell->nbits = info->nbits;
>>> @@ -382,13 +381,31 @@ static int nvmem_cell_info_to_nvmem_cell(struct nvmem_device *nvmem,
>>> if (!IS_ALIGNED(cell->offset, nvmem->stride)) {
>>> dev_err(&nvmem->dev,
>>> "cell %s unaligned to nvmem stride %d\n",
>>> - cell->name, nvmem->stride);
>>> + cell->name ?: "<unknown>", nvmem->stride);
>>> return -EINVAL;
>>> }
>>> return 0;
>>> }
>>> +static int
>>> +nvmem_cell_info_to_nvmem_cell(struct nvmem_device *nvmem,
>>> + const struct nvmem_cell_info *info,
>>> + struct nvmem_cell *cell)
>>> +{
>>> + int err;
>>> +
>>> + err = __nvmem_cell_info_to_nvmem_cell(nvmem, info, cell);
>>> + if (err)
>>> + return err;
>>> +
>>> + cell->name = kstrdup_const(info->name, GFP_KERNEL);
>>> + if (!cell->name)
>>> + return -ENOMEM;
>>> +
>>> + return 0;
>>> +}
>>> +
>>> /**
>>> * nvmem_add_cells() - Add cell information to an nvmem device
>>> *
>>> @@ -1460,7 +1477,7 @@ ssize_t nvmem_device_cell_read(struct nvmem_device *nvmem,
>>> if (!nvmem)
>>> return -EINVAL;
>>> - rc = nvmem_cell_info_to_nvmem_cell(nvmem, info, &cell);
>>> + rc = __nvmem_cell_info_to_nvmem_cell(nvmem, info, &cell);
>>> if (rc)
>>> return rc;
>>> @@ -1490,7 +1507,7 @@ int nvmem_device_cell_write(struct nvmem_device *nvmem,
>>> if (!nvmem)
>>> return -EINVAL;
>>> - rc = nvmem_cell_info_to_nvmem_cell(nvmem, info, &cell);
>>> + rc = __nvmem_cell_info_to_nvmem_cell(nvmem, info, &cell);
>>> if (rc)
>>> return rc;
>>>