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Date:   Wed, 18 Jul 2018 21:15:18 +0100
From:   Al Viro <viro@ZenIV.linux.org.uk>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Miklos Szeredi <mszeredi@redhat.com>,
        Stephen Rothwell <sfr@canb.auug.org.au>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] call_with_creds()
Message-ID: <20180718201518.GX30522@ZenIV.linux.org.uk>
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On Wed, Jul 18, 2018 at 09:04:11PM +0100, Al Viro wrote:
> On Wed, Jul 18, 2018 at 12:53:48PM -0700, Linus Torvalds wrote:
> > On Wed, Jul 18, 2018 at 12:46 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
> > >
> > > Huh?  Nevermind ->write(), what about open()?
> > 
> > What about open?
> > 
> > At open time, file->f_cred is the same as current_cred().
> 
> int cachefiles_write_page(struct fscache_storage *op, struct page *page)
> {
> ...
>         file = dentry_open(&path, O_RDWR | O_LARGEFILE, cache->cache_cred);
> 
> 
> int ecryptfs_privileged_open(struct file **lower_file,
>                              struct dentry *lower_dentry,
>                              struct vfsmount *lower_mnt,
>                              const struct cred *cred)
> ...
>         (*lower_file) = dentry_open(&req.path, flags, cred);

Actually, scratch that one - in this case it is current_cred() (whether that's
the right value or not).

cachefile_write_page() case is for real, AFAICS.