Daniel Axtens <dja@xxxxxxxxxx> writes: >> 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. Why is it good practice? It defeats -Wuninitialized. So you're guaranteed to be returning something initialised, but not necessarily initialised to the right value. In a case like this NULL seems like a safe choice, but it's still wrong. The function is meant to return a pointer to the successfully allocated fdt, or an ERR_PTR() value. NULL is neither of those. I agree there are security reasons that initialising stack variables is desirable, but I think that should be handled by the compiler, not at the source level. cheers
