[PATCH bpf] security: Fix hook iteration for secid_to_secctx

[Casey Schaufler]

On 5/20/2020 5:56 AM, KP Singh wrote:
> From: KP Singh <kpsingh at google.com>
>
> secid_to_secctx is not stackable, and since the BPF LSM registers this
> hook by default, the call_int_hook logic is not suitable which
> "bails-on-fail" and casues issues when other LSMs register this hook and
> eventually breaks Audit.
>
> In order to fix this, directly iterate over the security hooks instead
> of using call_int_hook as suggested in:
>
> https: //lore.kernel.org/bpf/9d0eb6c6-803a-ff3a-5603-9ad6d9edfc00 at schaufler-ca.com/#t
>
> Fixes: 98e828a0650f ("security: Refactor declaration of LSM hooks")
> Fixes: 625236ba3832 ("security: Fix the default value of secid_to_secctx hook"
> Reported-by: Alexei Starovoitov <ast at kernel.org>
> Signed-off-by: KP Singh <kpsingh at google.com>

This looks fine.

> ---
>  security/security.c | 16 ++++++++++++++--
>  1 file changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/security/security.c b/security/security.c
> index 7fed24b9d57e..51de970fbb1e 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -1965,8 +1965,20 @@ EXPORT_SYMBOL(security_ismaclabel);
>  
>  int security_secid_to_secctx(u32 secid, char **secdata, u32 *seclen)
>  {
> -	return call_int_hook(secid_to_secctx, -EOPNOTSUPP, secid, secdata,
> -				seclen);
> +	struct security_hook_list *hp;
> +	int rc;
> +
> +	/*
> +	 * Currently, only one LSM can implement secid_to_secctx (i.e this
> +	 * LSM hook is not "stackable").
> +	 */
> +	hlist_for_each_entry(hp, &security_hook_heads.secid_to_secctx, list) {
> +		rc = hp->hook.secid_to_secctx(secid, secdata, seclen);
> +		if (rc != LSM_RET_DEFAULT(secid_to_secctx))
> +			return rc;
> +	}
> +
> +	return LSM_RET_DEFAULT(secid_to_secctx);
>  }
>  EXPORT_SYMBOL(security_secid_to_secctx);
>