[RFC v2 bpf-next 6/7] bpf: devmap: check XDP features in bpf_map_update_elem and __xdp_enqueue

[Lorenzo Bianconi <lorenzo@xxxxxxxxxx>]

When we update devmap element, the net_device whose ifindex is specified
in map value must support ndo_xdp_xmit callback, which is indicated by
the presence of XDP_F_REDIRECT_TARGET feature. Let's check for
this feature and return an error if device cannot be used as a redirect
target.

Moreover check the device support xdp non-linear frame in __xdp_enqueue
and is_valid_dst routines. This patch allows to perfrom XDP_REDIRECT on
non-linear xdp buffers.

Co-developed-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
Signed-off-by: Lorenzo Bianconi <lorenzo@xxxxxxxxxx>
---
 kernel/bpf/devmap.c | 25 +++++++++++++++++++++----
 net/core/filter.c   | 13 +++++--------
 2 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index d01e4c55b376..69ceecc792df 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -474,7 +474,11 @@ static inline int __xdp_enqueue(struct net_device *dev, struct xdp_frame *xdpf,
 {
 	int err;
 
-	if (!dev->netdev_ops->ndo_xdp_xmit)
+	if (!(dev->xdp_features & NETDEV_XDP_ACT_NDO_XMIT))
+		return -EOPNOTSUPP;
+
+	if (unlikely(!(dev->xdp_features & NETDEV_XDP_ACT_NDO_XMIT_SG) &&
+		     xdp_frame_has_frags(xdpf)))
 		return -EOPNOTSUPP;
 
 	err = xdp_ok_fwd_dev(dev, xdp_get_frame_len(xdpf));
@@ -532,8 +536,14 @@ int dev_map_enqueue(struct bpf_dtab_netdev *dst, struct xdp_frame *xdpf,
 
 static bool is_valid_dst(struct bpf_dtab_netdev *obj, struct xdp_frame *xdpf)
 {
-	if (!obj ||
-	    !obj->dev->netdev_ops->ndo_xdp_xmit)
+	if (!obj)
+		return false;
+
+	if (!(obj->dev->xdp_features & NETDEV_XDP_ACT_NDO_XMIT))
+		return false;
+
+	if (unlikely(!(obj->dev->xdp_features & NETDEV_XDP_ACT_NDO_XMIT_SG) &&
+		     xdp_frame_has_frags(xdpf)))
 		return false;
 
 	if (xdp_ok_fwd_dev(obj->dev, xdp_get_frame_len(xdpf)))
@@ -843,6 +853,7 @@ static struct bpf_dtab_netdev *__dev_map_alloc_node(struct net *net,
 {
 	struct bpf_prog *prog = NULL;
 	struct bpf_dtab_netdev *dev;
+	int ret = -EINVAL;
 
 	dev = bpf_map_kmalloc_node(&dtab->map, sizeof(*dev),
 				   GFP_NOWAIT | __GFP_NOWARN,
@@ -854,6 +865,12 @@ static struct bpf_dtab_netdev *__dev_map_alloc_node(struct net *net,
 	if (!dev->dev)
 		goto err_out;
 
+	/* Check if net_device can be used as a redirect target */
+	if (!(READ_ONCE(dev->dev->xdp_features) & NETDEV_XDP_ACT_NDO_XMIT)) {
+		ret = -EOPNOTSUPP;
+		goto err_put_dev;
+	}
+
 	if (val->bpf_prog.fd > 0) {
 		prog = bpf_prog_get_type_dev(val->bpf_prog.fd,
 					     BPF_PROG_TYPE_XDP, false);
@@ -882,7 +899,7 @@ static struct bpf_dtab_netdev *__dev_map_alloc_node(struct net *net,
 	dev_put(dev->dev);
 err_out:
 	kfree(dev);
-	return ERR_PTR(-EINVAL);
+	return ERR_PTR(ret);
 }
 
 static int __dev_map_update_elem(struct net *net, struct bpf_map *map,
diff --git a/net/core/filter.c b/net/core/filter.c
index d9befa6ba04e..b9a03f1b2012 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4285,16 +4285,13 @@ int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
 	struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
 	enum bpf_map_type map_type = ri->map_type;
 
-	/* XDP_REDIRECT is not fully supported yet for xdp frags since
-	 * not all XDP capable drivers can map non-linear xdp_frame in
-	 * ndo_xdp_xmit.
-	 */
-	if (unlikely(xdp_buff_has_frags(xdp) &&
-		     map_type != BPF_MAP_TYPE_CPUMAP))
-		return -EOPNOTSUPP;
+	if (map_type == BPF_MAP_TYPE_XSKMAP) {
+		/* XDP_REDIRECT is not supported AF_XDP yet. */
+		if (unlikely(xdp_buff_has_frags(xdp)))
+			return -EOPNOTSUPP;
 
-	if (map_type == BPF_MAP_TYPE_XSKMAP)
 		return __xdp_do_redirect_xsk(ri, dev, xdp, xdp_prog);
+	}
 
 	return __xdp_do_redirect_frame(ri, dev, xdp_convert_buff_to_frame(xdp),
 				       xdp_prog);
-- 
2.39.0