Re: [PATCH bpf-next v2 07/11] bpf, sockmap: Return socket cookie on lookup from syscall

From: Martin Lau <kafai@fb.com>
To: Jakub Sitnicki <jakub@cloudflare.com>
Cc: "bpf@vger.kernel.org" <bpf@vger.kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"kernel-team@cloudflare.com" <kernel-team@cloudflare.com>,
	Eric Dumazet <edumazet@google.com>,
	"John Fastabend" <john.fastabend@gmail.com>,
	Lorenz Bauer <lmb@cloudflare.com>
Subject: Re: [PATCH bpf-next v2 07/11] bpf, sockmap: Return socket cookie on lookup from syscall
Date: Mon, 13 Jan 2020 23:12:26 +0000	[thread overview]
Message-ID: <20200113231223.cl77bxxs44bl6uhw@kafai-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <20200110105027.257877-8-jakub@cloudflare.com>

On Fri, Jan 10, 2020 at 11:50:23AM +0100, Jakub Sitnicki wrote:
> Tooling that populates the SOCKMAP with sockets from user-space needs a way
> to inspect its contents. Returning the struct sock * that SOCKMAP holds to
> user-space is neither safe nor useful. An approach established by
> REUSEPORT_SOCKARRAY is to return a socket cookie (a unique identifier)
> instead.
> 
> Since socket cookies are u64 values SOCKMAP needs to support such a value
> size for lookup to be possible. This requires special handling on update,
> though. Attempts to do a lookup on SOCKMAP holding u32 values will be met
> with ENOSPC error.
> 
> Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
> ---
>  net/core/sock_map.c | 31 +++++++++++++++++++++++++++++--
>  1 file changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/sock_map.c b/net/core/sock_map.c
> index d1a91e41ff82..3731191a7d1e 100644
> --- a/net/core/sock_map.c
> +++ b/net/core/sock_map.c
> @@ -10,6 +10,7 @@
>  #include <linux/skmsg.h>
>  #include <linux/list.h>
>  #include <linux/jhash.h>
> +#include <linux/sock_diag.h>
>  
>  struct bpf_stab {
>  	struct bpf_map map;
> @@ -31,7 +32,8 @@ static struct bpf_map *sock_map_alloc(union bpf_attr *attr)
>  		return ERR_PTR(-EPERM);
>  	if (attr->max_entries == 0 ||
>  	    attr->key_size    != 4 ||
> -	    attr->value_size  != 4 ||
> +	    (attr->value_size != sizeof(u32) &&
> +	     attr->value_size != sizeof(u64)) ||
>  	    attr->map_flags & ~SOCK_CREATE_FLAG_MASK)
>  		return ERR_PTR(-EINVAL);
>  
> @@ -298,6 +300,23 @@ static void *sock_map_lookup(struct bpf_map *map, void *key)
>  	return ERR_PTR(-EOPNOTSUPP);
>  }
>  
> +static void *sock_map_lookup_sys(struct bpf_map *map, void *key)
> +{
> +	struct sock *sk;
> +
> +	WARN_ON_ONCE(!rcu_read_lock_held());
It seems unnecessary.  It is only called by syscall.c which
holds the rcu_read_lock().  Other than that,

Acked-by: Martin KaFai Lau <kafai@fb.com>

> +
> +	if (map->value_size != sizeof(u64))
> +		return ERR_PTR(-ENOSPC);
> +
> +	sk = __sock_map_lookup_elem(map, *(u32 *)key);
> +	if (!sk)
> +		return ERR_PTR(-ENOENT);
> +
> +	sock_gen_cookie(sk);
> +	return &sk->sk_cookie;
> +}
> +