# \[PATCH net-next v3 30/33\] xdp: clear grow memory in bpf\_xdp\_adjust\_tail()

- From: Jesper Dangaard Brouer \<hidden\>
- Date: 2020-05-08 11:11:34 
- List: netdev
- Page: https://ratatoskr.run/netdev/2020/05/7733736
- Thread: https://ratatoskr.run/netdev/2020/05/7733706/t.md

```text
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 <redacted>
Acked-by: Toke Høiland-Jørgensen <redacted>
---
 net/core/filter.c |    4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/core/filter.c b/net/core/filter.c
index ec3ab2e2d800..691235208e0b 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3427,6 +3427,10 @@ 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;


```