Merge branch 'AF_XDP Socket Creation Fixes'

Ciara Loftus says:

====================

This series fixes some issues around socket creation for AF_XDP.

Patch 1 fixes a potential NULL pointer dereference in
xsk_socket__create_shared.

Patch 2 ensures that the umem passed to xsk_socket__create(_shared)
remains unchanged in event of failure.

Patch 3 makes it possible for xsk_socket__create(_shared) to
succeed even if the rx and tx XDP rings have already been set up by
introducing a new fields to struct xsk_umem which represent the ring
setup status for the xsk which shares the fd with the umem.

v3->v4:
* Reduced nesting in xsk_put_ctx as suggested by Alexei.
* Use bools instead of a u8 and flags to represent the
  ring setup status as suggested by Björn.

v2->v3:
* Instead of ignoring the return values of the setsockopt calls, introduce
  a new flag to determine whether or not to call them based on the ring
  setup status as suggested by Alexei.

v1->v2:
* Simplified restoring the _save pointers as suggested by Magnus.
* Fixed the condition which determines whether to unmap umem rings
 when socket create fails.

====================

Acked-by: Björn Töpel <bjorn@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/lib/bpf/xsk.c

@@ -59,6 +59,8 @@ struct xsk_umem {
 	int fd;
 	int refcount;
 	struct list_head ctx_list;
+	bool rx_ring_setup_done;
+	bool tx_ring_setup_done;
 };
 
 struct xsk_ctx {
@@ -743,26 +745,30 @@ static struct xsk_ctx *xsk_get_ctx(struct xsk_umem *umem, int ifindex,
 	return NULL;
 }
 
-static void xsk_put_ctx(struct xsk_ctx *ctx)
+static void xsk_put_ctx(struct xsk_ctx *ctx, bool unmap)
 {
 	struct xsk_umem *umem = ctx->umem;
 	struct xdp_mmap_offsets off;
 	int err;
 
-	if (--ctx->refcount == 0) {
-		err = xsk_get_mmap_offsets(umem->fd, &off);
-		if (!err) {
-			munmap(ctx->fill->ring - off.fr.desc,
-			       off.fr.desc + umem->config.fill_size *
-			       sizeof(__u64));
-			munmap(ctx->comp->ring - off.cr.desc,
-			       off.cr.desc + umem->config.comp_size *
-			       sizeof(__u64));
-		}
+	if (--ctx->refcount)
+		return;
 
-		list_del(&ctx->list);
-		free(ctx);
-	}
+	if (!unmap)
+		goto out_free;
+
+	err = xsk_get_mmap_offsets(umem->fd, &off);
+	if (err)
+		goto out_free;
+
+	munmap(ctx->fill->ring - off.fr.desc, off.fr.desc + umem->config.fill_size *
+	       sizeof(__u64));
+	munmap(ctx->comp->ring - off.cr.desc, off.cr.desc + umem->config.comp_size *
+	       sizeof(__u64));
+
+out_free:
+	list_del(&ctx->list);
+	free(ctx);
 }
 
 static struct xsk_ctx *xsk_create_ctx(struct xsk_socket *xsk,
@@ -797,8 +803,6 @@ static struct xsk_ctx *xsk_create_ctx(struct xsk_socket *xsk,
 	memcpy(ctx->ifname, ifname, IFNAMSIZ - 1);
 	ctx->ifname[IFNAMSIZ - 1] = '\0';
 
-	umem->fill_save = NULL;
-	umem->comp_save = NULL;
 	ctx->fill = fill;
 	ctx->comp = comp;
 	list_add(&ctx->list, &umem->ctx_list);
@@ -854,6 +858,8 @@ int xsk_socket__create_shared(struct xsk_socket **xsk_ptr,
 	struct xsk_socket *xsk;
 	struct xsk_ctx *ctx;
 	int err, ifindex;
+	bool unmap = umem->fill_save != fill;
+	bool rx_setup_done = false, tx_setup_done = false;
 
 	if (!umem || !xsk_ptr || !(rx || tx))
 		return -EFAULT;
@@ -881,6 +887,8 @@ int xsk_socket__create_shared(struct xsk_socket **xsk_ptr,
 		}
 	} else {
 		xsk->fd = umem->fd;
+		rx_setup_done = umem->rx_ring_setup_done;
+		tx_setup_done = umem->tx_ring_setup_done;
 	}
 
 	ctx = xsk_get_ctx(umem, ifindex, queue_id);
@@ -899,23 +907,27 @@ int xsk_socket__create_shared(struct xsk_socket **xsk_ptr,
 	}
 	xsk->ctx = ctx;
 
-	if (rx) {
+	if (rx && !rx_setup_done) {
 		err = setsockopt(xsk->fd, SOL_XDP, XDP_RX_RING,
 				 &xsk->config.rx_size,
 				 sizeof(xsk->config.rx_size));
 		if (err) {
 			err = -errno;
 			goto out_put_ctx;
 		}
+		if (xsk->fd == umem->fd)
+			umem->rx_ring_setup_done = true;
 	}
-	if (tx) {
+	if (tx && !tx_setup_done) {
 		err = setsockopt(xsk->fd, SOL_XDP, XDP_TX_RING,
 				 &xsk->config.tx_size,
 				 sizeof(xsk->config.tx_size));
 		if (err) {
 			err = -errno;
 			goto out_put_ctx;
 		}
+		if (xsk->fd == umem->fd)
+			umem->rx_ring_setup_done = true;
 	}
 
 	err = xsk_get_mmap_offsets(xsk->fd, &off);
@@ -994,6 +1006,8 @@ int xsk_socket__create_shared(struct xsk_socket **xsk_ptr,
 	}
 
 	*xsk_ptr = xsk;
+	umem->fill_save = NULL;
+	umem->comp_save = NULL;
 	return 0;
 
 out_mmap_tx:
@@ -1005,7 +1019,7 @@ int xsk_socket__create_shared(struct xsk_socket **xsk_ptr,
 		munmap(rx_map, off.rx.desc +
 		       xsk->config.rx_size * sizeof(struct xdp_desc));
 out_put_ctx:
-	xsk_put_ctx(ctx);
+	xsk_put_ctx(ctx, unmap);
 out_socket:
 	if (--umem->refcount)
 		close(xsk->fd);
@@ -1019,6 +1033,9 @@ int xsk_socket__create(struct xsk_socket **xsk_ptr, const char *ifname,
 		       struct xsk_ring_cons *rx, struct xsk_ring_prod *tx,
 		       const struct xsk_socket_config *usr_config)
 {
+	if (!umem)
+		return -EFAULT;
+
 	return xsk_socket__create_shared(xsk_ptr, ifname, queue_id, umem,
 					 rx, tx, umem->fill_save,
 					 umem->comp_save, usr_config);
@@ -1068,7 +1085,7 @@ void xsk_socket__delete(struct xsk_socket *xsk)
 		}
 	}
 
-	xsk_put_ctx(ctx);
+	xsk_put_ctx(ctx, true);
 
 	umem->refcount--;
 	/* Do not close an fd that also has an associated umem connected