Re: [PATCH] CIFS: unlock file across process

[Murphy Zhou <jencce.kernel@gmail.com>]

On Fri, Feb 14, 2020 at 07:26:46AM -0500, Jeff Layton wrote:
> On Fri, 2020-02-14 at 12:35 +0800, Murphy Zhou wrote:
> > Now child can't unlock the same file that has been locked by
> > parent. Fix this by not skipping unlock if requesting from
> > different process.
> > 
> > Patch tested by LTP and xfstests using samba server.
> > 
> > Signed-off-by: Murphy Zhou <jencce.kernel@gmail.com>
> > ---
> >  fs/cifs/smb2file.c | 2 --
> >  1 file changed, 2 deletions(-)
> > 
> > diff --git a/fs/cifs/smb2file.c b/fs/cifs/smb2file.c
> > index afe1f03aabe3..b5bca0e13d51 100644
> > --- a/fs/cifs/smb2file.c
> > +++ b/fs/cifs/smb2file.c
> > @@ -151,8 +151,6 @@ smb2_unlock_range(struct cifsFileInfo *cfile, struct file_lock *flock,
> >  		    (flock->fl_start + length) <
> >  		    (li->offset + li->length))
> >  			continue;
> > -		if (current->tgid != li->pid)
> > -			continue;
> >  		if (cinode->can_cache_brlcks) {
> >  			/*
> >  			 * We can cache brlock requests - simply remove a lock
> 
> I'm not as familiar with this code as I once was, but...
> 
> From fork(2) manpage:
> 
>        *  The  child does not inherit process-associated record locks from its
>           parent (fcntl(2)).  (On the other hand,  it  does  inherit  fcntl(2)
>           open file description locks and flock(2) locks from its parent.)
> 
> It looks like cifs_setlk calls mand_unlock_range, and that gets called
> from both fcntl and flock codepaths.
> 
> So, I'm not sure about just removing this. It seems like the pid check
> is probably correct for traditional posix locks, but probably not for
> OFD and flock locks? What ensures that completely unrelated tasks can't
> unlock your locks?

You are right Jeff. Just removing this is not right. We need to handle
at least 3 types of locks: posix, OFD and flock.

Thanks very much for reviewing! I'll try to sort this out.
> -- 
> Jeff Layton <jlayton@kernel.org>
>