Re: [PATCH RFC] NFSD: fix cannot umounting mount points under pseudo root

[NeilBrown <neilb@suse.com>]

On Sat, 27 Jun 2015 07:14:00 +0800 Kinglong Mee <kinglongmee@gmail.com>
wrote:

> ping ....
> 
> > -----------------------------------------------------------------------------------
> >>From d831154bb7e527f9003e16ac049526be5ed90228 Mon Sep 17 00:00:00 2001
> > From: Kinglong Mee <kinglongmee@gmail.com>
> > Date: Tue, 5 May 2015 16:24:16 +0800
> > Subject: [PATCH] mountd: Case-insensitive path length must equals to parent
> > 
> > Commit 6091c0a4c4 (mountd: add support for case-insensitive file names)
> > introduces looking up bad path which is easy to trigger a present mutex race.
> > 

How do you know that every file system that treats multiple different
strings as the same, imposes the rule that the strings must be the same
length?

Given how complex unicode case rules can be, I certainly wouldn't be
certain of that.

If the only purpose of this patch is to avoid triggering a bug in a
separate piece of code, then I am not in favour of it.

Thanks,
NeilBrown


> > Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
> > ---
> >  utils/mountd/cache.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/utils/mountd/cache.c b/utils/mountd/cache.c
> > index 7d250f9..155695a 100644
> > --- a/utils/mountd/cache.c
> > +++ b/utils/mountd/cache.c
> > @@ -478,7 +478,7 @@ static int is_subdirectory(char *child, char *parent)
> >  	if (strcmp(parent, "/") == 0 && child[1] != 0)
> >  		return 1;
> >  
> > -	return (same_path(child, parent, l) && child[l] == '/');
> > +	return (child[l] == '/'	&& same_path(child, parent, l));
> >  }
> >  
> >  static int path_matches(nfs_export *exp, char *path)
> >