linux-kernel - Re: [PATCH v4] selinux: fix a missing-check bug in selinux_add_mnt

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Message-ID: <CAHC9VhTVpTMBHDWtXVBcW94-Rt2jzW0-+D_krgyj6o3TotodwQ@mail.gmail.com>
Date:   Wed, 12 Jun 2019 12:16:31 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Gen Zhang <blackgod016574@...il.com>
Cc:     Stephen Smalley <sds@...ho.nsa.gov>,
        Eric Paris <eparis@...isplace.org>, selinux@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] selinux: fix a missing-check bug in
 selinux_add_mnt_opt( )

On Wed, Jun 12, 2019 at 9:28 AM Gen Zhang <blackgod016574@...il.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@...il.com>
> Fixes: 757cbe597fe8 ("LSM: new method: ->sb_add_mnt_opt()")
> ---
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 3ec702c..b4b888e 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -1052,15 +1052,24 @@ 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;
> +                       }

This block has an extra indent, but I'll go ahead and fix that during
the merge.  I have to mention that had you run this patch through
./scripts/checkpatch.pl it would have caught the mistake :)

Regardless, thanks for the patch, I've merged it into the
selinux/stable-5.2 branch and I'll be testing it shortly.

> +       }
>         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;
> +
> +free_opt:
> +       if (*mnt_opts) {
> +               selinux_free_mnt_opts(*mnt_opts);
> +               *mnt_opts = NULL;
>         }
>         return rc;
>  }

-- 
paul moore
www.paul-moore.com