linux-kernel - Re: [PATCH v2] hooks: fix a missing-check bug in selinux_add_mnt

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Date:   Sat, 1 Jun 2019 09:54:42 +0800
From:   Gen Zhang <blackgod016574@...il.com>
To:     Paul Moore <paul@...l-moore.com>
Cc:     Ondrej Mosnacek <omosnace@...hat.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Eric Paris <eparis@...isplace.org>, ccross@...roid.com,
        selinux@...r.kernel.org,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>,
        netdev@...r.kernel.org
Subject: Re: [PATCH v2] hooks: fix a missing-check bug in
 selinux_add_mnt_opt()

On Fri, May 31, 2019 at 11:55:23AM -0400, Paul Moore wrote:
> On Thu, May 30, 2019 at 4:55 AM Gen Zhang <blackgod016574@...il.com> wrote:
> >
> > In selinux_add_mnt_opt(), 'val' is allcoted by kmemdup_nul(). It returns
> > NULL when fails. So 'val' should be checked.
> >
> > Signed-off-by: Gen Zhang <blackgod016574@...il.com>
> > Fixes: 757cbe597fe8 ("LSM: new method: ->sb_add_mnt_opt()")
> 
> Previous comments regarding "selinux:" instead of "hooks:" apply here as well.
> 
Thanks for your comments, Paul. I will make some changes.
> > diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> > index 3ec702c..4797c63 100644
> > --- a/security/selinux/hooks.c
> > +++ b/security/selinux/hooks.c
> > @@ -1052,8 +1052,11 @@ 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)
> > +                               return -ENOMEM;
> 
> It looks like this code is only ever called by NFS, which will
> eventually clean up mnt_opts via security_free_mnt_opts(), but since
> the selinux_add_opt() error handler below cleans up mnt_opts it might
> be safer to do the same here in case this function is called multiple
> times to add multiple options.
> 
> > +       }
> >         rc = selinux_add_opt(token, val, mnt_opts);
> >         if (unlikely(rc)) {
> >                 kfree(val);
> 
> -- 
> paul moore
> www.paul-moore.com
Thanks
Gen