Re: [PATCH V2] Fix NULL dereference in super_by_fd

[Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>]

On Mon, 19 Dec 2022 19:50:52 +0800
lixiaokeng <lixiaokeng@huawei.com> wrote:

> On 2022/12/15 19:50, Mariusz Tkaczyk wrote:
> > On Wed, 14 Dec 2022 11:17:41 +0800
> > lixiaokeng <lixiaokeng@huawei.com> wrote:
> >   
> >> strcpy(st->devnm, devnm);  
> > 
> > Hi,
> > Please use strncpy or snprintf here.  
> 
> Thanks for your advice, but the length of devnm is not
> a defined value. I will keep it as the old codes.

Supertype devnm is a array defined to be 32.
https://git.kernel.org/pub/scm/utils/mdadm/mdadm.git/tree/mdadm.h#n1256

32 should be changed to MD_NAME_MAX - you can use this define.
I traveled fd2devnm and I can see that at the end devid2devnm returns:
static char devnm[32]
https://git.kernel.org/pub/scm/utils/mdadm/mdadm.git/tree/lib.c#n123

For that reason usage of strcpy in this case seems to be safe, unless we change
something deeper. My recommendation comes from general safe development rules-
we know dest buffer size so we can esnure that it will be ended properly by
'\0', whatever comes to write from fd2devnm().

Thanks,
Mariusz