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

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Message-ID: <CAFqZXNvM94T2reUsn6Mwuz6GNGNCR=wUNBE8w4tcjNuhJ6rCeQ@mail.gmail.com>
Date:   Fri, 7 Jun 2019 10:41:17 +0200
From:   Ondrej Mosnacek <omosnace@...hat.com>
To:     Gen Zhang <blackgod016574@...il.com>
Cc:     Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <sds@...ho.nsa.gov>,
        Eric Paris <eparis@...isplace.org>, selinux@...r.kernel.org,
        Linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] selinux: lsm: fix a missing-check bug in
 selinux_sb_eat_lsm_o pts()

On Thu, Jun 6, 2019 at 10:55 AM Gen Zhang <blackgod016574@...il.com> wrote:
> In selinux_sb_eat_lsm_opts(), 'arg' is allocated by kmemdup_nul(). It
> returns NULL when fails. So 'arg' should be checked. And 'mnt_opts'
> should be freed when error.
>
> Signed-off-by: Gen Zhang <blackgod016574@...il.com>
> Fixes: 99dbbb593fe6 ("selinux: rewrite selinux_sb_eat_lsm_opts()")

My comments about the subject and an empty line before label apply
here as well, but Paul can fix both easily when applying, so:

Reviewed-by: Ondrej Mosnacek <omosnace@...hat.com>

> ---
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 3ec702c..13479cd 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2616,10 +2616,11 @@ static int selinux_sb_eat_lsm_opts(char *options, void **mnt_opts)
>         char *from = options;
>         char *to = options;
>         bool first = true;
> +       int rc;
>
>         while (1) {
>                 int len = opt_len(from);
> -               int token, rc;
> +               int token;
>                 char *arg = NULL;
>
>                 token = match_opt_prefix(from, len, &arg);
> @@ -2635,15 +2636,15 @@ static int selinux_sb_eat_lsm_opts(char *options, void **mnt_opts)
>                                                 *q++ = c;
>                                 }
>                                 arg = kmemdup_nul(arg, q - arg, GFP_KERNEL);
> +                               if (!arg) {
> +                                       rc = -ENOMEM;
> +                                       goto free_opt;
> +                               }
>                         }
>                         rc = selinux_add_opt(token, arg, mnt_opts);
>                         if (unlikely(rc)) {
>                                 kfree(arg);
> -                               if (*mnt_opts) {
> -                                       selinux_free_mnt_opts(*mnt_opts);
> -                                       *mnt_opts = NULL;
> -                               }
> -                               return rc;
> +                               goto free_opt;
>                         }
>                 } else {
>                         if (!first) {   // copy with preceding comma
> @@ -2661,6 +2662,12 @@ static int selinux_sb_eat_lsm_opts(char *options, void **mnt_opts)
>         }
>         *to = '\0';
>         return 0;
> +free_opt:
> +       if (*mnt_opts) {
> +               selinux_free_mnt_opts(*mnt_opts);
> +               *mnt_opts = NULL;
> +       }
> +       return rc;
>  }
>
>  static int selinux_sb_remount(struct super_block *sb, void *mnt_opts)

--
Ondrej Mosnacek <omosnace at redhat dot com>
Software Engineer, Security Technologies
Red Hat, Inc.