Re: [PATCH v3] selinux: lsm: fix a missing-check bug in selinux_add_mnt_opt( )

[Gen Zhang <blackgod016574@gmail.com>]

On Fri, Jun 07, 2019 at 10:39:05AM +0200, Ondrej Mosnacek wrote:
> On Thu, Jun 6, 2019 at 11:23 AM Gen Zhang <blackgod016574@gmail.com> wrote:
> > In selinux_add_mnt_opt(), 'val' is allocated by kmemdup_nul(). It returns
> > NULL when fails. So 'val' should be checked. And 'mnt_opts' should be
> > freed when error.
> >
> > Signed-off-by: Gen Zhang <blackgod016574@gmail.com>
> > Fixes: 757cbe597fe8 ("LSM: new method: ->sb_add_mnt_opt()")
> > ---
> > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > index 3ec702c..4e4c1c6 100644
> > --- a/security/selinux/hooks.c
> > +++ b/security/selinux/hooks.c
> > @@ -1052,15 +1052,23 @@ static int selinux_add_mnt_opt(const char *option, const char *val, int len,
> >         if (token == Opt_error)
> >                 return -EINVAL;
> >
> > -       if (token != Opt_seclabel)
> > -               val = kmemdup_nul(val, len, GFP_KERNEL);
> > +       if (token != Opt_seclabel) {
> > +                       val = kmemdup_nul(val, len, GFP_KERNEL);
> > +                       if (!val) {
> > +                               rc = -ENOMEM;
> > +                               goto free_opt;
> > +                       }
> > +       }
> >         rc = selinux_add_opt(token, val, mnt_opts);
> >         if (unlikely(rc)) {
> >                 kfree(val);
> > -               if (*mnt_opts) {
> > -                       selinux_free_mnt_opts(*mnt_opts);
> > -                       *mnt_opts = NULL;
> > -               }
> > +               goto free_opt;
> > +       }
> > +       return rc;
> 
> At this point rc is guaranteed to be 0, so you can just 'return 0' for
> clarity. Also, I visually prefer an empty line between a return
> statement and a goto label, but I'm not sure what is the
> general/maintainer's preference.
Am I supposed to revise and send a patch v4 for this, or let the 
maintainer do this? :-)

Thanks
Gen
> 
> Also, you should drop the "lsm: " from the subject - it is redundant
> and doesn't follow the SELinux convention. See `git log --oneline --
> security/selinux/` for what the subjects usually look like - mostly we
> just go with "selinux: <description>" (or "LSM: <description>" when
> the changes affect the shared LSM interface).
Thanks for your comments.
> 
> > +free_opt:
> > +       if (*mnt_opts) {
> > +               selinux_free_mnt_opts(*mnt_opts);
> > +               *mnt_opts = NULL;
> >         }
> >         return rc;
> >  }
> 
> --
> Ondrej Mosnacek <omosnace at redhat dot com>
> Software Engineer, Security Technologies
> Red Hat, Inc.