linux-kernel - Re: [PATCH v4 4/4] ovl: Optimize override/revert creds

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Message-ID: <CAOQ4uxh01iN5QPWtSDJPAR0Z0mhAj691PXYJeroSO8WvzxgfAg@mail.gmail.com>
Date: Fri, 15 Nov 2024 09:16:09 +0100
From: Amir Goldstein <amir73il@...il.com>
To: Vinicius Costa Gomes <vinicius.gomes@...el.com>
Cc: brauner@...nel.org, miklos@...redi.hu, hu1.chen@...el.com, 
	malini.bhandaru@...el.com, tim.c.chen@...el.com, mikko.ylinen@...el.com, 
	linux-unionfs@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/4] ovl: Optimize override/revert creds

On Thu, Nov 14, 2024 at 10:01 PM Vinicius Costa Gomes
<vinicius.gomes@...el.com> wrote:
>
> Amir Goldstein <amir73il@...il.com> writes:
>
> > On Thu, Nov 14, 2024 at 9:56 AM Amir Goldstein <amir73il@...il.com> wrote:
> >>
> >> On Wed, Nov 13, 2024 at 8:30 PM Vinicius Costa Gomes
> >> <vinicius.gomes@...el.com> wrote:
> >> >
> >> > Amir Goldstein <amir73il@...il.com> writes:
> >> >
> >> > > On Thu, Nov 7, 2024 at 1:57 AM Vinicius Costa Gomes
> >> > > <vinicius.gomes@...el.com> wrote:
> >> >
> >> > [...]
> >> >
> >> > >
> >> > > Vinicius,
> >> > >
> >> > > While testing fanotify with LTP tests (some are using overlayfs),
> >> > > kmemleak consistently reports the problems below.
> >> > >
> >> > > Can you see the bug, because I don't see it.
> >> > > Maybe it is a false positive...
> >> >
> >> > Hm, if the leak wasn't there before and we didn't touch anything related to
> >> > prepare_creds(), I think that points to the leak being real.
> >> >
> >> > But I see your point, still not seeing it.
> >> >
> >> > This code should be equivalent to the code we have now (just boot
> >> > tested):
> >> >
> >> > ----
> >> > diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
> >> > index 136a2c7fb9e5..7ebc2fd3097a 100644
> >> > --- a/fs/overlayfs/dir.c
> >> > +++ b/fs/overlayfs/dir.c
> >> > @@ -576,8 +576,7 @@ static int ovl_setup_cred_for_create(struct dentry *dentry, struct inode *inode,
> >> >          * We must be called with creator creds already, otherwise we risk
> >> >          * leaking creds.
> >> >          */
> >> > -       WARN_ON_ONCE(override_creds(override_cred) != ovl_creds(dentry->d_sb));
> >> > -       put_cred(override_cred);
> >> > +       WARN_ON_ONCE(override_creds_light(override_cred) != ovl_creds(dentry->d_sb));
> >> >
> >> >         return 0;
> >> >  }
> >> > ----
> >> >
> >> > Does it change anything? (I wouldn't think so, just to try something)
> >>
> >> No, but I think this does:
> >>
> >
> > Vinicius,
> >
> > Sorry, your fix is correct. I did not apply it properly when I tested.
> >
> > I edited the comment as follows and applied on top of the patch
> > that I just sent [1]:
> >
>
> I just noticed there's a typo in the first sentence of the commit
> message, the function name that we are using revert_creds_light() is
> ovl_revert_creds(). Could you fix that while you are at it?
>

fixed.

Thanks,
Amir.