[PATCH 5.15.y] xen-netfront: handle NULL returned by xdp_convert_buff_to_frame()

[Johnny Hao]

From: Alexey Nepomnyashih <sdl@xxxxxxxx>

[ Upstream commit cc3628dcd851ddd8d418bf0c897024b4621ddc92 ]

The function xdp_convert_buff_to_frame() may return NULL if it fails
to correctly convert the XDP buffer into an XDP frame due to memory
constraints, internal errors, or invalid data. Failing to check for NULL
may lead to a NULL pointer dereference if the result is used later in
processing, potentially causing crashes, data corruption, or undefined
behavior.

On XDP redirect failure, the associated page must be released explicitly
if it was previously retained via get_page(). Failing to do so may result
in a memory leak, as the pages reference count is not decremented.

Cc: stable@xxxxxxxxxxxxxxx # v5.9+
Fixes: 6c5aa6fc4def ("xen networking: add basic XDP support for xen-netfront")
Signed-off-by: Alexey Nepomnyashih <sdl@xxxxxxxx>
Link: https://patch.msgid.link/20250417122118.1009824-1-sdl@xxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Johnny Hao <johnny_haocn@xxxxxxxx>
---
 drivers/net/xen-netfront.c | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 4b19d54fa2e2..310bc1f7d404 100644
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -982,20 +982,27 @@ static u32 xennet_run_xdp(struct netfront_queue *queue, struct page *pdata,
 	act = bpf_prog_run_xdp(prog, xdp);
 	switch (act) {
 	case XDP_TX:
-		get_page(pdata);
 		xdpf = xdp_convert_buff_to_frame(xdp);
+		if (unlikely(!xdpf)) {
+			trace_xdp_exception(queue->info->netdev, prog, act);
+			break;
+		}
+		get_page(pdata);
 		err = xennet_xdp_xmit(queue->info->netdev, 1, &xdpf, 0);
-		if (unlikely(!err))
+		if (unlikely(err <= 0)) {
+			if (err < 0)
+				trace_xdp_exception(queue->info->netdev, prog, act);
 			xdp_return_frame_rx_napi(xdpf);
-		else if (unlikely(err < 0))
-			trace_xdp_exception(queue->info->netdev, prog, act);
+		}
 		break;
 	case XDP_REDIRECT:
 		get_page(pdata);
 		err = xdp_do_redirect(queue->info->netdev, xdp, prog);
 		*need_xdp_flush = true;
-		if (unlikely(err))
+		if (unlikely(err)) {
 			trace_xdp_exception(queue->info->netdev, prog, act);
+			xdp_return_buff(xdp);
+		}
 		break;
 	case XDP_PASS:
 	case XDP_DROP:
-- 
2.34.1