[PATCH batadv v2] batman-adv: tvlv: enforce 2-byte alignment

The fields of an aggregated OGM(v2) are accessed assuming (at least) 2-byte
alignment, so a following OGM must start at an even offset. As the header
length is even, an odd tvlv_len would misalign it and trigger unaligned
accesses on strict-alignment architectures.

Such a misaligned TVLV/OGM/OGMv2/MCAST is not created by a normal
participant in the mesh. Therefore, reject such malformed packets.

Fixes: 0b6aa0d43767 ("batman-adv: tvlv - basic infrastructure")
Signed-off-by: Sven Eckelmann <[email protected]>
---
Changes in v2:
- also handle batadv_recv_mcast_packet()
- remove RFC
- Link to v1: https://patch.msgid.link/[email protected]
---
 net/batman-adv/bat_iv_ogm.c | 11 ++++++++++-
 net/batman-adv/bat_v_ogm.c  | 11 ++++++++++-
 net/batman-adv/routing.c    |  6 ++++++
 net/batman-adv/tvlv.c       |  6 ++++++
 4 files changed, 32 insertions(+), 2 deletions(-)

diff --git a/net/batman-adv/bat_iv_ogm.c b/net/batman-adv/bat_iv_ogm.c
index 7588e64e..bb2f012b 100644
--- a/net/batman-adv/bat_iv_ogm.c
+++ b/net/batman-adv/bat_iv_ogm.c
@@ -316,14 +316,23 @@ batadv_iv_ogm_aggr_packet(int buff_pos, int packet_len,
 			  const struct batadv_ogm_packet *ogm_packet)
 {
 	int next_buff_pos = 0;
+	u16 tvlv_len;
 
 	/* check if there is enough space for the header */
 	next_buff_pos += buff_pos + sizeof(*ogm_packet);
 	if (next_buff_pos > packet_len)
 		return false;
 
+	tvlv_len = ntohs(ogm_packet->tvlv_len);
+
+	/* the fields of an aggregated OGM are accessed assuming (at least)
+	 * 2-byte alignment, so a following OGM must start at an even offset.
+	 */
+	if (tvlv_len & 1)
+		return false;
+
 	/* check if there is enough space for the optional TVLV */
-	next_buff_pos += ntohs(ogm_packet->tvlv_len);
+	next_buff_pos += tvlv_len;
 
 	return next_buff_pos <= packet_len;
 }
diff --git a/net/batman-adv/bat_v_ogm.c b/net/batman-adv/bat_v_ogm.c
index 95efd8a4..037921aa 100644
--- a/net/batman-adv/bat_v_ogm.c
+++ b/net/batman-adv/bat_v_ogm.c
@@ -849,14 +849,23 @@ batadv_v_ogm_aggr_packet(int buff_pos, int packet_len,
 			 const struct batadv_ogm2_packet *ogm2_packet)
 {
 	int next_buff_pos = 0;
+	u16 tvlv_len;
 
 	/* check if there is enough space for the header */
 	next_buff_pos += buff_pos + sizeof(*ogm2_packet);
 	if (next_buff_pos > packet_len)
 		return false;
 
+	tvlv_len = ntohs(ogm2_packet->tvlv_len);
+
+	/* the fields of an aggregated OGMv2 are accessed assuming (at least)
+	 * 2-byte alignment, so a following OGMv2 must start at an even offset.
+	 */
+	if (tvlv_len & 1)
+		return false;
+
 	/* check if there is enough space for the optional TVLV */
-	next_buff_pos += ntohs(ogm2_packet->tvlv_len);
+	next_buff_pos += tvlv_len;
 
 	return next_buff_pos <= packet_len;
 }
diff --git a/net/batman-adv/routing.c b/net/batman-adv/routing.c
index 9db57fd3..c05fcc92 100644
--- a/net/batman-adv/routing.c
+++ b/net/batman-adv/routing.c
@@ -1366,6 +1366,12 @@ int batadv_recv_mcast_packet(struct sk_buff *skb,
 	if (tvlv_buff_len > skb->len - hdr_size)
 		goto free_skb;
 
+	/* the fields of an multicast payload are accessed assuming (at least)
+	 * 2-byte alignment, so a following packet must start at an even offset.
+	 */
+	if (tvlv_buff_len & 1)
+		goto free_skb;
+
 	ret = batadv_tvlv_containers_process(bat_priv, BATADV_MCAST, NULL, skb,
 					     tvlv_buff, tvlv_buff_len);
 	if (ret >= 0) {
diff --git a/net/batman-adv/tvlv.c b/net/batman-adv/tvlv.c
index 403c8545..a957555d 100644
--- a/net/batman-adv/tvlv.c
+++ b/net/batman-adv/tvlv.c
@@ -477,6 +477,12 @@ int batadv_tvlv_containers_process(struct batadv_priv *bat_priv,
 		if (tvlv_value_cont_len > tvlv_value_len)
 			break;
 
+		/* the next tvlv header is accessed assuming (at least) 2-byte
+		 * alignment, so it must start at an even offset.
+		 */
+		if (tvlv_value_cont_len & 1)
+			break;
+
 		tvlv_handler = batadv_tvlv_handler_get(bat_priv,
 						       tvlv_hdr->type,
 						       tvlv_hdr->version);

---
base-commit: c7518adb8b6ebdc481f6ed1fc42c7f45099806af
change-id: 20260614-tvlv-2b-align-f11bc4263342

Best regards,
--  
Sven Eckelmann <[email protected]>