[PATCH] ipv6: ndisc: fix potential out-of-bounds read in ndisc_router_discovery()

[Rafal Bilkowski <rafalbilkowski@gmail.com>]

This patch adds a length check at the start of ndisc_router_discovery()
to prevent a potential out-of-bounds read if a short packet is received.
Without this check, the function may dereference memory outside the
buffer.

Fixes: 8610c7c6e3bd ("net: ipv6: add support for rpl sr exthdr")
Signed-off-by: Rafal Bilkowski <rafalbilkowski@gmail.com>
---
 net/ipv6/ndisc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/ipv6/ndisc.c b/net/ipv6/ndisc.c
index 8d853971f2f6..bdaac5a195d6 100644
--- a/net/ipv6/ndisc.c
+++ b/net/ipv6/ndisc.c
@@ -1235,6 +1235,10 @@ static void ndisc_ra_useropt(struct sk_buff *ra, struct nd_opt_hdr *opt)
 
 static enum skb_drop_reason ndisc_router_discovery(struct sk_buff *skb)
 {
+	// Check if the buffer contains enough data for the struct ra_msg
+	if (!pskb_may_pull(skb, skb_transport_offset(skb) + sizeof(struct ra_msg)))
+		return SKB_DROP_REASON_PKT_TOO_SMALL;
+
 	struct ra_msg *ra_msg = (struct ra_msg *)skb_transport_header(skb);
 	bool send_ifinfo_notify = false;
 	struct neighbour *neigh = NULL;
-- 
2.43.0