On Wed, 19 Aug 2020 15:13:49 +0200
Lorenzo Bianconi [off-list ref] wrote:

quoted

diff --git a/net/core/xdp.c b/net/core/xdp.c
index 884f140fc3be..006b24b5d276 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c

@@ -370,19 +370,55 @@ static void __xdp_return(void *data, struct xdp_mem_info *mem, bool napi_direct)
 
 void xdp_return_frame(struct xdp_frame *xdpf)
 {
+	struct skb_shared_info *sinfo;
+	int i;
+
 	__xdp_return(xdpf->data, &xdpf->mem, false);

There is a use-after-free race here.  The xdpf->data contains the
shared_info (xdp_get_shared_info_from_frame(xdpf)). Thus you cannot
free/return the page and use this data area below.

right, thx for pointing this out. I will fix it in v2.

Regards,
Lorenzo

quoted

+	if (!xdpf->mb)
+		return;
+
+	sinfo = xdp_get_shared_info_from_frame(xdpf);
+	for (i = 0; i < sinfo->nr_frags; i++) {
+		struct page *page = skb_frag_page(&sinfo->frags[i]);
+
+		__xdp_return(page_address(page), &xdpf->mem, false);
+	}
 }
 EXPORT_SYMBOL_GPL(xdp_return_frame);
 
 void xdp_return_frame_rx_napi(struct xdp_frame *xdpf)
 {
+	struct skb_shared_info *sinfo;
+	int i;
+
 	__xdp_return(xdpf->data, &xdpf->mem, true);

Same issue.

quoted

+	if (!xdpf->mb)
+		return;
+
+	sinfo = xdp_get_shared_info_from_frame(xdpf);
+	for (i = 0; i < sinfo->nr_frags; i++) {
+		struct page *page = skb_frag_page(&sinfo->frags[i]);
+
+		__xdp_return(page_address(page), &xdpf->mem, true);
+	}
 }
 EXPORT_SYMBOL_GPL(xdp_return_frame_rx_napi);
 
 void xdp_return_buff(struct xdp_buff *xdp)
 {
+	struct skb_shared_info *sinfo;
+	int i;
+
 	__xdp_return(xdp->data, &xdp->rxq->mem, true);

Same issue.

quoted

+	if (!xdp->mb)
+		return;
+
+	sinfo = xdp_get_shared_info_from_buff(xdp);
+	for (i = 0; i < sinfo->nr_frags; i++) {
+		struct page *page = skb_frag_page(&sinfo->frags[i]);
+
+		__xdp_return(page_address(page), &xdp->rxq->mem, true);
+	}
 }

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer