[PATCH v2 3/8] vfs: Add O_DENYREAD/WRITE flags support for open syscall

[J. Bruce Fields]

On Thu, Feb 07, 2013 at 08:50:16PM +0400, Pavel Shilovsky wrote:
> 2013/2/7 J. Bruce Fields <bfields at fieldses.org>:
> > That would be a bug, I think.  E.g. "man 3posix open":
> >
> >         No  files  shall  be created or modified if the function returns
> >         -1.
> >
> > Looking at the code...  See the references to FILE_CREATED in
> > atomic_open--looks like that's trying to prevent may_open from failing
> > in this case.
> >
> >> I think
> >> there is no difference between this case and the situation with
> >> deny_lock_file there.
> >
> > Looks to me like it would be a bug in either case.
> 
> Then we returned from lookup_open in do_last we go to 'opened' lable.
> Then we have a 3(!) chances to return -1 while a file is created
> (open_check_o_direct, ima_file_check, handle_truncate

I don't know about the first two, but handle_truncate won't be hit since
will_truncate is false.

> ). In this case
> these places are bugs too.
> 
> We can call vfs_unlink if we failed after a file was created, but
> possible affects need to be investigated.

We definitely don't want to try to undo the create with an unlink.

--b.