Re: [PATCH V2] xfs: fix string handling in get/set functions

[Eric Sandeen]

On 6/6/18 5:58 AM, Christoph Hellwig wrote:
>> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
>> index 82f7c83c1dad..596e176c19a6 100644
>> --- a/fs/xfs/xfs_ioctl.c
>> +++ b/fs/xfs/xfs_ioctl.c
>> @@ -1828,13 +1828,13 @@ xfs_ioc_getlabel(
>>  	/* Paranoia */
>>  	BUILD_BUG_ON(sizeof(sbp->sb_fname) > FSLABEL_MAX);
>>  
>> +	/* 1 larger than sb_fname, so this ensures a trailing NUL char */
>> +	memset(label, 0, sizeof(label));
> 
> I don't get the comment.  In fact I don't even get why we need any
> comment here.  This is a structure that gets copied to userspace,
> and we zero the whole structure, as we should do by default for
> anything that goes to userspace.

Sure, I guess we didn't really need the comment, my main point was that
we were guaranteed to have a \0 remaining at the end because we'd never copy
over it due to sb_fname's smaller size.

> Otherwise this looks fine to me.

Thanks.  In retrospect we could have gone back to Arnd's original patch
but I guess the explicit memset is ... well, nice and explicit.

-Eric