Re: [PATCH 1/1] xskmap: reject TX-only AF_XDP sockets

[Maciej Fijalkowski]

On Mon, Mar 30, 2026 at 03:29:42AM +0800, Linpu Yu wrote:
> Reject TX-only AF_XDP sockets from XSKMAP updates. Redirected
> packets always enter the Rx path, where the kernel expects the
> selected socket to have an Rx ring. A TX-only socket can
> currently be inserted into an XSKMAP, and redirecting a packet
> to it crashes the kernel in xsk_generic_rcv().

This paragraph seems to be strictly related to veth nature. While the fix
makes sense to me, it should be stated that it is not a default behavior
but rather how veth works.

> 
> Keep TX-only AF_XDP sockets valid for pure Tx use, but prevent
> them from being published through XSKMAP.
> 
> Fixes: fbfc504a24f5 ("bpf: introduce new bpf AF_XDP map type BPF_MAP_TYPE_XSKMAP")
> Reported-by: Juefei Pu <tomapufckgml@xxxxxxxxx>
> Reported-by: Yuan Tan <yuantan098@xxxxxxxxx>
> Signed-off-by: Xin Liu <bird@xxxxxxxxxx>
> Signed-off-by: Yifan Wu <yifanwucs@xxxxxxxxx>
> Signed-off-by: Linpu Yu <linpu5433@xxxxxxxxx>
> ---
>  net/xdp/xskmap.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/net/xdp/xskmap.c b/net/xdp/xskmap.c
> index afa457506274c..6dac59ebb5cf0 100644
> --- a/net/xdp/xskmap.c
> +++ b/net/xdp/xskmap.c
> @@ -184,6 +184,10 @@ static long xsk_map_update_elem(struct bpf_map *map, void *key, void *value,
>  	}
>  
>  	xs = (struct xdp_sock *)sock->sk;
> +	if (!READ_ONCE(xs->rx)) {
> +		sockfd_put(sock);
> +		return -EINVAL;
> +	}
>  
>  	map_entry = &m->xsk_map[i];
>  	node = xsk_map_node_alloc(m, map_entry);
> -- 
> 2.53.0
>