[PATCH 6.1 24/25] batman-adv: tvlv: enforce 2-byte alignment

[Sven Eckelmann <sven@narfation.org>]

commit 32a6799255525d6ea4da0f7e9e0e521ad9560a46 upstream.

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 is not created by a normal participant in
the mesh. Therefore, reject such malformed packets.

Cc: stable@kernel.org
Fixes: ef26157747d4 ("batman-adv: tvlv - basic infrastructure")
[ Drop change for non-existing mcast handling ]
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
 net/batman-adv/bat_iv_ogm.c | 11 ++++++++++-
 net/batman-adv/bat_v_ogm.c  | 11 ++++++++++-
 net/batman-adv/tvlv.c       |  6 ++++++
 3 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/net/batman-adv/bat_iv_ogm.c b/net/batman-adv/bat_iv_ogm.c
index c52e3b8288986..7fd692b642e39 100644
--- a/net/batman-adv/bat_iv_ogm.c
+++ b/net/batman-adv/bat_iv_ogm.c
@@ -311,14 +311,23 @@ 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 f87c2b80e4291..e8ad4817d2001 100644
--- a/net/batman-adv/bat_v_ogm.c
+++ b/net/batman-adv/bat_v_ogm.c
@@ -854,14 +854,23 @@ 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/tvlv.c b/net/batman-adv/tvlv.c
index 99e5e8518dcc9..e25430da5afb1 100644
--- a/net/batman-adv/tvlv.c
+++ b/net/batman-adv/tvlv.c
@@ -448,6 +448,12 @@ 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);
-- 
2.47.3