[PATCH net 1/2] ioam6: fix write to cloned skb in ipv6_hop_ioam()

[Justin Iurman]

ioam6_fill_trace_data() writes inside the skb payload without ensuring
it's writeable (e.g., not cloned). This function is called both from the
input and output path. The output path (ioam6_iptunnel) already does the
check. This commit provides a fix for the input path, inside
ipv6_hop_ioam().

Fixes: 9ee11f0fff20 ("ipv6: ioam: Data plane support for Pre-allocated Trace ")
Reported-by: Paolo Abeni <pabeni@xxxxxxxxxx>
Signed-off-by: Justin Iurman <justin.iurman@xxxxxxxxx>
---
 net/ipv6/exthdrs.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
index 4952ae792450..f68e5faab3aa 100644
--- a/net/ipv6/exthdrs.c
+++ b/net/ipv6/exthdrs.c
@@ -943,6 +943,14 @@ static bool ipv6_hop_ioam(struct sk_buff *skb, int optoff)
 		if (!skb_valid_dst(skb))
 			ip6_route_input(skb);
 
+		if (skb_cloned(skb)) {
+			if (pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+				goto drop;
+
+			hdr = (struct ioam6_hdr *)(skb_network_header(skb) + optoff);
+			trace = (struct ioam6_trace_hdr *)((u8 *)hdr + sizeof(*hdr));
+		}
+
 		ioam6_fill_trace_data(skb, ns, trace, true);
 		break;
 	default:
-- 
2.34.1