Re: [PATCH] powerpc: Initialize local variable fdt to NULL in elf64_load()

[Daniel Axtens <dja@axtens.net>]

Hi Lakshmi,

> On 4/15/21 12:14 PM, Lakshmi Ramasubramanian wrote:
>
> Sorry - missed copying device-tree and powerpc mailing lists.
>
>> There are a few "goto out;" statements before the local variable "fdt"
>> is initialized through the call to of_kexec_alloc_and_setup_fdt() in
>> elf64_load(). This will result in an uninitialized "fdt" being passed
>> to kvfree() in this function if there is an error before the call to
>> of_kexec_alloc_and_setup_fdt().
>> 
>> Initialize the local variable "fdt" to NULL.
>>
I'm a huge fan of initialising local variables! But I'm struggling to
find the code path that will lead to an uninit fdt being returned...

The out label reads in part:

	/* Make kimage_file_post_load_cleanup free the fdt buffer for us. */
	return ret ? ERR_PTR(ret) : fdt;

As far as I can tell, any time we get a non-zero ret, we're going to
return an error pointer rather than the uninitialised value...

(btw, it does look like we might leak fdt if we have an error after we
successfully kmalloc it.)

Am I missing something? Can you link to the report for the kernel test
robot or from Dan? 

FWIW, I think it's worth including this patch _anyway_ because initing
local variables is good practice, but I'm just not sure on the
justification.

Kind regards,
Daniel

>> Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
>> Reported-by: kernel test robot <lkp@intel.com>
>> Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
>> ---
>>   arch/powerpc/kexec/elf_64.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/arch/powerpc/kexec/elf_64.c b/arch/powerpc/kexec/elf_64.c
>> index 5a569bb51349..0051440c1f77 100644
>> --- a/arch/powerpc/kexec/elf_64.c
>> +++ b/arch/powerpc/kexec/elf_64.c
>> @@ -32,7 +32,7 @@ static void *elf64_load(struct kimage *image, char *kernel_buf,
>>   	int ret;
>>   	unsigned long kernel_load_addr;
>>   	unsigned long initrd_load_addr = 0, fdt_load_addr;
>> -	void *fdt;
>> +	void *fdt = NULL;
>>   	const void *slave_code;
>>   	struct elfhdr ehdr;
>>   	char *modified_cmdline = NULL;
>> 
>
> thanks,
>   -lakshmi