[PATCH RFC v2 30/33] xdp: clear grow memory in bpf_xdp_adjust_tail()

[Jesper Dangaard Brouer <brouer@xxxxxxxxxx>]

Clearing memory of tail when grow happens, because it is too easy
to write a XDP_PASS program that extend the tail, which expose
this memory to users that can run tcpdump.

Signed-off-by: Jesper Dangaard Brouer <brouer@xxxxxxxxxx>
---
 net/core/filter.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/core/filter.c b/net/core/filter.c
index 4d58a147eed0..a8674f2a0e24 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3445,6 +3445,11 @@ BPF_CALL_2(bpf_xdp_adjust_tail, struct xdp_buff *, xdp, int, offset)
 	if (unlikely(data_end < xdp->data + ETH_HLEN))
 		return -EINVAL;
 
+	/* Clear memory area on grow, can contain uninit kernel memory */
+	if (offset > 0) {
+		memset(xdp->data_end, 0, offset);
+	}
+
 	xdp->data_end = data_end;
 
 	return 0;