[RFC PATCH v1 1/2] landlock: Fix non-TCP sockets restriction

[Mickaël Salaün]

Please also add Matthieu in Cc for the network patch series.

On Thu, Oct 03, 2024 at 10:39:31PM +0800, Mikhail Ivanov wrote:
> Do not check TCP access right if socket protocol is not IPPROTO_TCP.
> LANDLOCK_ACCESS_NET_BIND_TCP and LANDLOCK_ACCESS_NET_CONNECT_TCP
> should not restrict bind(2) and connect(2) for non-TCP protocols
> (SCTP, MPTCP, SMC).
> 
> Closes: https://github.com/landlock-lsm/linux/issues/40
> Fixes: fff69fb03dde ("landlock: Support network rules with TCP bind and connect")
> Signed-off-by: Mikhail Ivanov <ivanov.mikhail1 at huawei-partners.com>
> ---
>  security/landlock/net.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/security/landlock/net.c b/security/landlock/net.c
> index bc3d943a7118..6f59dd98bb13 100644
> --- a/security/landlock/net.c
> +++ b/security/landlock/net.c
> @@ -68,7 +68,7 @@ static int current_check_access_socket(struct socket *const sock,
>  		return -EACCES;
>  
>  	/* Checks if it's a (potential) TCP socket. */

We can extend this comment to explain that we don't use sk_is_tcp()
because we need to handle the AF_UNSPEC case.

> -	if (sock->type != SOCK_STREAM)
> +	if (sock->type != SOCK_STREAM || sock->sk->sk_protocol != IPPROTO_TCP)

I think we should check sock->sk->sk_type instead of sock->type (even if
it should be the same).  To make it simpler, we should only use sk in
current_check_access_socket():
struct sock *sk = sock->sk;

Could you please also do s/__sk_common\.skc_/sk_/g ?

>  		return 0;
>  
>  	/* Checks for minimal header length to safely read sa_family. */
> -- 
> 2.34.1
> 
>