On Thu, Nov 14, 2024 at 9:56 AM Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>
> On Wed, Nov 13, 2024 at 8:30 PM Vinicius Costa Gomes
> <vinicius.gomes@xxxxxxxxx> wrote:
> >
> > Amir Goldstein <amir73il@xxxxxxxxx> writes:
> >
> > > On Thu, Nov 7, 2024 at 1:57 AM Vinicius Costa Gomes
> > > <vinicius.gomes@xxxxxxxxx> 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]:
- put_cred(override_creds(override_cred));
+
+ /*
+ * Caller is going to match this with revert_creds_light() and drop
+ * reference on the returned creds.
+ * We must be called with creator creds already, otherwise we risk
+ * leaking creds.
+ */
+ old_cred = override_creds_light(override_cred);
+ WARN_ON_ONCE(old_cred != ovl_creds(dentry->d_sb));
return override_cred;
Thanks,
Amir.
[1] https://lore.kernel.org/linux-unionfs/20241114100536.628162-1-amir73il@xxxxxxxxx/
