bpf, test_run: Fix LIVE_FRAME frame update after a page has been recycled

The test_run code detects whether a page has been modified and
re-initialises the xdp_frame structure if it has, using
xdp_update_frame_from_buff(). However, xdp_update_frame_from_buff()
doesn't touch frame->mem, so that wasn't correctly re-initialised, which
led to the pages from page_pool not being returned correctly. Syzbot
noticed this as a memory leak.

Fix this by also copying the frame->mem structure when re-initialising
the frame, like we do on initialisation of a new page from page_pool.

Fixes: e5995bc ("bpf, test_run: fix crashes due to XDP frame overwriting/corruption")
Fixes: b530e9e ("bpf: Add "live packet" mode for XDP in BPF_PROG_RUN")
Reported-by: [email protected]
Signed-off-by: Toke Høiland-Jørgensen <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Tested-by: [email protected]
Reviewed-by: Alexander Lobakin <[email protected]>
Acked-by: Stanislav Fomichev <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

Author: tohojo

net/bpf/test_run.c

@@ -246,6 +246,7 @@ static void reset_ctx(struct xdp_page_head *head)
 	head->ctx.data_meta = head->orig_ctx.data_meta;
 	head->ctx.data_end = head->orig_ctx.data_end;
 	xdp_update_frame_from_buff(&head->ctx, head->frame);
+	head->frame->mem = head->orig_ctx.rxq->mem;
 }
 
 static int xdp_recv_frames(struct xdp_frame **frames, int nframes,