[RFC PATCH] smack: fix access permissions for keyring

[Casey Schaufler]

On 10/17/2018 4:25 PM, Zoran Markovic wrote:
> Function smack_key_permission() only issues smack requests for the
> following operations:
>  - KEY_NEED_READ (issues MAY_READ)
>  - KEY_NEED_WRITE (issues MAY_WRITE)
>  - KEY_NEED_LINK (issues MAY_WRITE)
>  - KEY_NEED_SETATTR (issues MAY_WRITE)
> A blank smack request is issued in all other cases, resulting in
> smack access being granted if there is any rule defined between
> subject and object, or denied with -EACCES otherwise.
>
> Request MAY_READ access for KEY_NEED_SEARCH and KEY_NEED_VIEW.
> Fix the logic in the unlikely case when both MAY_READ and
> MAY_WRITE are needed. Validate access permission field for valid
> contents.

Do you have any test cases for this?

> Signed-off-by: Zoran Markovic <zmarkovic at sierrawireless.com>
> Cc: Casey Schaufler <casey at schaufler-ca.com>
> Cc: James Morris <jmorris at namei.org>
> Cc: "Serge E. Hallyn" <serge at hallyn.com>
> ---
>  security/smack/smack_lsm.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 340fc30..77e405f 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -4326,6 +4326,12 @@ static int smack_key_permission(key_ref_t key_ref,
>  	int request = 0;
>  	int rc;
>  
> +	/*
> +	 * Validate requested permissions
> +	 */
> +	if (perm & ~KEY_NEED_ALL)
> +		return -EINVAL;
> +
>  	keyp = key_ref_to_ptr(key_ref);
>  	if (keyp == NULL)
>  		return -EINVAL;
> @@ -4349,10 +4355,10 @@ static int smack_key_permission(key_ref_t key_ref,
>  	ad.a.u.key_struct.key = keyp->serial;
>  	ad.a.u.key_struct.key_desc = keyp->description;
>  #endif
> -	if (perm & KEY_NEED_READ)
> -		request = MAY_READ;
> +	if (perm & (KEY_NEED_READ | KEY_NEED_SEARCH | KEY_NEED_VIEW))
> +		request |= MAY_READ;
>  	if (perm & (KEY_NEED_WRITE | KEY_NEED_LINK | KEY_NEED_SETATTR))
> -		request = MAY_WRITE;
> +		request |= MAY_WRITE;
>  	rc = smk_access(tkp, keyp->security, request, &ad);
>  	rc = smk_bu_note("key access", tkp, keyp->security, request, rc);
>  	return rc;