From: Jesper Dangaard Brouer <brouer@redhat.com>
Date: Thu, 14 May 2020 12:51:30 +0200
Subject: xdp: Clear grow memory in bpf_xdp_adjust_tail()
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Patch-mainline: v5.8-rc1
Git-commit: ddb47d518ca10948d1f64a983cb9274720f691cd
References: bsc#1177028

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@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/158945349039.97035.5262100484553494.stgit@firesoul
Acked-by: Gary Lin <glin@suse.com>
---
 net/core/filter.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3427,6 +3427,10 @@ BPF_CALL_2(bpf_xdp_adjust_tail, struct x
 	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;