xen-netfront: handle NULL returned by xdp_convert_buff_to_frame()

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@vger.kernel.org # v5.9+
Fixes: 6c5aa6fc4def ("xen networking: add basic XDP support for xen-netfront")
Signed-off-by: Alexey Nepomnyashih <sdl@nppct.ru>
Link: https://patch.msgid.link/20250417122118.1009824-1-sdl@nppct.ru
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index fc52d5c4c69b700211b09328aaf5f4075ad9d3a2..5091e1fa4a0df63358c93c0a18bbba62bd097d3a 100644 (file)
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -985,20 +985,27 @@ 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: