Re: [PATCH] nvdimm: Fix devs leaks in scan_labels()

["Zhijian Li (Fujitsu)" <lizhijian@fujitsu.com>]

On 07/06/2024 00:27, Dave Jiang wrote:
> 
> 
> On 6/3/24 8:16 PM, Li Zhijian wrote:
>> Don't allocate devs again when it's valid pointer which has pionted to
>> the memory allocated above with size (count + 2 * sizeof(dev)).
>>
>> A kmemleak reports:
>> unreferenced object 0xffff88800dda1980 (size 16):
>>    comm "kworker/u10:5", pid 69, jiffies 4294671781
>>    hex dump (first 16 bytes):
>>      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
>>    backtrace (crc 0):
>>      [<00000000c5dea560>] __kmalloc+0x32c/0x470
>>      [<000000009ed43c83>] nd_region_register_namespaces+0x6fb/0x1120 [libnvdimm]
>>      [<000000000e07a65c>] nd_region_probe+0xfe/0x210 [libnvdimm]
>>      [<000000007b79ce5f>] nvdimm_bus_probe+0x7a/0x1e0 [libnvdimm]
>>      [<00000000a5f3da2e>] really_probe+0xc6/0x390
>>      [<00000000129e2a69>] __driver_probe_device+0x78/0x150
>>      [<000000002dfed28b>] driver_probe_device+0x1e/0x90
>>      [<00000000e7048de2>] __device_attach_driver+0x85/0x110
>>      [<0000000032dca295>] bus_for_each_drv+0x85/0xe0
>>      [<00000000391c5a7d>] __device_attach+0xbe/0x1e0
>>      [<0000000026dabec0>] bus_probe_device+0x94/0xb0
>>      [<00000000c590d936>] device_add+0x656/0x870
>>      [<000000003d69bfaa>] nd_async_device_register+0xe/0x50 [libnvdimm]
>>      [<000000003f4c52a4>] async_run_entry_fn+0x2e/0x110
>>      [<00000000e201f4b0>] process_one_work+0x1ee/0x600
>>      [<000000006d90d5a9>] worker_thread+0x183/0x350
>>
>> Fixes: 1b40e09a1232 ("libnvdimm: blk labels and namespace instantiation")
>> Signed-off-by: Li Zhijian <lizhijian@fujitsu.com>
>> ---
>>   drivers/nvdimm/namespace_devs.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/nvdimm/namespace_devs.c b/drivers/nvdimm/namespace_devs.c
>> index d6d558f94d6b..56b016dbe307 100644
>> --- a/drivers/nvdimm/namespace_devs.c
>> +++ b/drivers/nvdimm/namespace_devs.c
>> @@ -1994,7 +1994,9 @@ static struct device **scan_labels(struct nd_region *nd_region)
>>   		/* Publish a zero-sized namespace for userspace to configure. */
>>   		nd_mapping_free_labels(nd_mapping);
>>   
>> -		devs = kcalloc(2, sizeof(dev), GFP_KERNEL);
>> +		/* devs probably has been allocated */
>> +		if (!devs)
>> +			devs = kcalloc(2, sizeof(dev), GFP_KERNEL);
> 
> This changes the behavior of this code and possibly corrupting the previously allocated memory at times when 'devs' is valid.

If we reach here, that means count == 0 is true. so we can deduce that
the previously allocated memory was not touched at all in previous loop.
and its size was (2 * sizeof(dev)) too.

Was the 'devs' leaked out from the previous loop and should be freed instead?

this option is also fine to me. we can also fix this by free(devs) before allocate it again.:

+             kfree(devs); // kfree(NULL) is safe.
               devs = kcalloc(2, sizeof(dev), GFP_KERNEL);


Thanks
Zhijian

> 
>>   		if (!devs)
>>   			goto err;
>>   
>