Re: [RFC PATCH] libsepol: validate permission identifier length

From: Stephen Smalley <stephen.smalley.work@gmail.com>
To: "Christian Göttsche" <cgzones@googlemail.com>
Cc: selinux@vger.kernel.org
Subject: Re: [RFC PATCH] libsepol: validate permission identifier length
Date: Fri, 8 Dec 2023 11:05:51 -0500	[thread overview]
Message-ID: <CAEjxPJ4htnqzDyHFNR_aNJH-hrz_wbM=Z=NN7BjUQDrKBa8e9A@mail.gmail.com> (raw)
In-Reply-To: <20231207165319.63889-1-cgzones@googlemail.com>

On Thu, Dec 7, 2023 at 11:53 AM Christian Göttsche
<cgzones@googlemail.com> wrote:
>
> Limit the maximum length of permission identifiers.  Otherwise
> formatting an access vector might fail in the common used helper
> sepol_av_to_string().
>
> The current longest permission within the Reference Policy is
> x_application_data { paste_after_confirm } with a length of 19.

Android has longer permission names. I'd rather just fix
sepol_av_to_string() than impose some arbitrary limit here.

>
> Reported-by: oss-fuzz (issue 64832)
> Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
> ---
> The oss-fuzz issue got closed by the latest fuzzer updates (due to
> unrelated changes that invalid the current reproducer), but the issue is
> still valid.
> ---
>  libsepol/src/policydb_validate.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/libsepol/src/policydb_validate.c b/libsepol/src/policydb_validate.c
> index bd8e9f8f..72681120 100644
> --- a/libsepol/src/policydb_validate.c
> +++ b/libsepol/src/policydb_validate.c
> @@ -366,12 +366,30 @@ bad:
>         return -1;
>  }
>
> +static int validate_permission_wrapper(hashtab_key_t k, __attribute__((unused)) hashtab_datum_t d, void *args)
> +{
> +       sepol_handle_t *handle = args;
> +       const char *name = k;
> +       size_t len = strlen(name);
> +
> +       if (len == 0 || len >= 32)
> +               goto bad;
> +
> +       return 0;
> +
> +bad:
> +       ERR(handle, "Invalid permission");
> +       return -1;
> +}
> +
>  static int validate_common_datum(sepol_handle_t *handle, const common_datum_t *common, validate_t flavors[])
>  {
>         if (validate_value(common->s.value, &flavors[SYM_COMMONS]))
>                 goto bad;
>         if (common->permissions.table->nel == 0 || common->permissions.nprim > PERM_SYMTAB_SIZE)
>                 goto bad;
> +       if (hashtab_map(common->permissions.table, validate_permission_wrapper, handle))
> +               goto bad;
>
>         return 0;
>
> @@ -395,6 +413,8 @@ static int validate_class_datum(sepol_handle_t *handle, const class_datum_t *cla
>                 goto bad;
>         if (class->permissions.nprim > PERM_SYMTAB_SIZE)
>                 goto bad;
> +       if (hashtab_map(class->permissions.table, validate_permission_wrapper, handle))
> +               goto bad;
>         if (validate_constraint_nodes(handle, class->permissions.nprim, class->constraints, flavors))
>                 goto bad;
>         if (validate_constraint_nodes(handle, 0, class->validatetrans, flavors))
> --
> 2.43.0
>
>