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

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Message-ID: <CAHC9VhSwzD652qKUy7qrRJ=zy-NZtKRGc7H4NZurzUcK4OgFZA@mail.gmail.com>
Date:   Fri, 31 May 2019 11:55:23 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Gen Zhang <blackgod016574@...il.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 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.

> 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