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

[Ondrej Mosnacek]

On Sat, Jun 1, 2019 at 4:15 AM Gen Zhang <blackgod016574@xxxxxxxxx> 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@xxxxxxxxx>
> Reviewed-by: Ondrej Mosnacek <omosnace@xxxxxxxxxx>
> Fixes: 99dbbb593fe6 ("selinux: rewrite selinux_sb_eat_lsm_opts()")
> ---
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 3ec702c..f329fc0 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2616,6 +2616,7 @@ static int selinux_sb_eat_lsm_opts(char *options, void **mnt_opts)
>         char *from = options;
>         char *to = options;
>         bool first = true;
> +       int ret;

I'd suggest just moving the declaration of 'rc' here and simply reuse
that variable. Otherwise the patch looks good to me.

>
>         while (1) {
>                 int len = opt_len(from);
> @@ -2635,15 +2636,16 @@ static int selinux_sb_eat_lsm_opts(char *options, void **mnt_opts)
>                                                 *q++ = c;
>                                 }
>                                 arg = kmemdup_nul(arg, q - arg, GFP_KERNEL);
> +                               if (!arg) {
> +                                       ret = -ENOMEM;
> +                                       goto free_opt;
> +                               }
>                         }
>                         rc = selinux_add_opt(token, arg, mnt_opts);
>                         if (unlikely(rc)) {
> +                               ret = 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 +2663,12 @@ 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 ret;
>  }
>
>  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.