[PATCH] selinux,smack: properly reference the LSM blob in security_watch_key()

[Casey Schaufler]

On 9/19/2024 8:57 AM, Paul Moore wrote:
> Unfortunately when we migrated the lifecycle management of the key LSM
> blob to the LSM framework we forgot to convert the security_watch_key()
> callbacks for SELinux and Smack.  This patch corrects this by making use
> of the selinux_key() and smack_key() helper functions respectively.
>
> This patch also removes some input checking in the Smack callback as it
> is no longer needed.
>
> Reported-by: syzbot+044fdf24e96093584232 at syzkaller.appspotmail.com
> Fixes: 5f8d28f6d7d5 ("lsm: infrastructure management of the key security blob")
> Signed-off-by: Paul Moore <paul at paul-moore.com>

Reviewed-by: Casey Schaufler <casey at schaufler-ca.com>

> ---
>  security/selinux/hooks.c   |  2 +-
>  security/smack/smack_lsm.c | 13 +++----------
>  2 files changed, 4 insertions(+), 11 deletions(-)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 81fbfa5b80d4..67baa487cf7a 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -6720,7 +6720,7 @@ static int selinux_key_getsecurity(struct key *key, char **_buffer)
>  #ifdef CONFIG_KEY_NOTIFICATIONS
>  static int selinux_watch_key(struct key *key)
>  {
> -	struct key_security_struct *ksec = key->security;
> +	struct key_security_struct *ksec = selinux_key(key);
>  	u32 sid = current_sid();
>  
>  	return avc_has_perm(sid, ksec->sid, SECCLASS_KEY, KEY__VIEW, NULL);
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index da0c2bffbd08..563fb404f659 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -4629,16 +4629,9 @@ static int smack_watch_key(struct key *key)
>  {
>  	struct smk_audit_info ad;
>  	struct smack_known *tkp = smk_of_current();
> +	struct smack_known **blob = smack_key(key);
>  	int rc;
>  
> -	if (key == NULL)
> -		return -EINVAL;
> -	/*
> -	 * If the key hasn't been initialized give it access so that
> -	 * it may do so.
> -	 */
> -	if (key->security == NULL)
> -		return 0;
>  	/*
>  	 * This should not occur
>  	 */
> @@ -4653,8 +4646,8 @@ static int smack_watch_key(struct key *key)
>  	ad.a.u.key_struct.key = key->serial;
>  	ad.a.u.key_struct.key_desc = key->description;
>  #endif
> -	rc = smk_access(tkp, key->security, MAY_READ, &ad);
> -	rc = smk_bu_note("key watch", tkp, key->security, MAY_READ, rc);
> +	rc = smk_access(tkp, *blob, MAY_READ, &ad);
> +	rc = smk_bu_note("key watch", tkp, *blob, MAY_READ, rc);
>  	return rc;
>  }
>  #endif /* CONFIG_KEY_NOTIFICATIONS */