From 38eaed28e250895d56f4b7989bd65479a511c5c3 Mon Sep 17 00:00:00 2001 From: Sven Eckelmann Date: Fri, 3 Jul 2026 20:47:45 +0200 Subject: [PATCH] batman-adv: mcast: avoid OOB read of num_dests header Before the access to struct batadv_tvlv_mcast_tracker's num_dests, it is attempted to check whether enough space is actually in the network header. But instead of using offsetofend() to check for the whole size (2) which must be accessible, offsetof() of is called. The latter is always returning 0. The comparison with the network header length will always return that enough data is available - even when only 1 or 0 bytes are accessible. Instead of using offsetofend(), use the more common check for the whole header. Cc: stable@vger.kernel.org Fixes: 07afe1ba288c ("batman-adv: mcast: implement multicast packet reception and forwarding") Signed-off-by: Sven Eckelmann --- net/batman-adv/multicast_forw.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/net/batman-adv/multicast_forw.c b/net/batman-adv/multicast_forw.c index b8668a80b94a..1404a3b7adfb 100644 --- a/net/batman-adv/multicast_forw.c +++ b/net/batman-adv/multicast_forw.c @@ -927,11 +927,11 @@ static int batadv_mcast_forw_packet(struct batadv_priv *bat_priv, { struct batadv_tvlv_mcast_tracker *mcast_tracker; struct batadv_neigh_node *neigh_node; - unsigned long offset, num_dests_off; struct sk_buff *nexthop_skb; unsigned char *skb_net_hdr; bool local_recv = false; unsigned int tvlv_len; + unsigned long offset; bool xmitted = false; u8 *dest, *next_dest; u16 num_dests; @@ -940,9 +940,8 @@ static int batadv_mcast_forw_packet(struct batadv_priv *bat_priv, /* (at least) TVLV part needs to be linearized */ SKB_LINEAR_ASSERT(skb); - /* check if num_dests is within skb length */ - num_dests_off = offsetof(struct batadv_tvlv_mcast_tracker, num_dests); - if (num_dests_off > skb_network_header_len(skb)) + /* check if batadv_tvlv_mcast_tracker header is within skb length */ + if (sizeof(*mcast_tracker) > skb_network_header_len(skb)) return -EINVAL; skb_net_hdr = skb_network_header(skb); -- 2.47.3