batman-adv: Only read OGM tvlv_len after buffer len check

Multiple batadv_ogm_packet can be stored in an skbuff. The functions
batadv_iv_ogm_send_to_if()/batadv_iv_ogm_receive() use
batadv_iv_ogm_aggr_packet() to check if there is another additional
batadv_ogm_packet in the skb or not before they continue processing the
packet.

The length for such an OGM is BATADV_OGM_HLEN +
batadv_ogm_packet->tvlv_len. The check must first check that at least
BATADV_OGM_HLEN bytes are available before it accesses tvlv_len (which is
part of the header. Otherwise it might try read outside of the currently
available skbuff to get the content of tvlv_len.

Fixes: ef26157747d4 ("batman-adv: tvlv - basic infrastructure")
Reported-by: syzbot+355cab184197dbbfa384@syzkaller.appspotmail.com
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Acked-by: Antonio Quartulli <a@unstable.cc>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>

1 files changed, 13 insertions, 7 deletions

diff --git a/net/batman-adv/bat_iv_ogm.c b/net/batman-adv/bat_iv_ogm.c
index 240ed70912d6..d78938e3e008 100644
--- a/net/batman-adv/bat_iv_ogm.c
+++ b/net/batman-adv/bat_iv_ogm.c
@@ -277,17 +277,23 @@ static u8 batadv_hop_penalty(u8 tq, const struct batadv_priv *bat_priv)
  * batadv_iv_ogm_aggr_packet() - checks if there is another OGM attached
  * @buff_pos: current position in the skb
  * @packet_len: total length of the skb
- * @tvlv_len: tvlv length of the previously considered OGM
+ * @ogm_packet: potential OGM in buffer
  *
  * Return: true if there is enough space for another OGM, false otherwise.
  */
-static bool batadv_iv_ogm_aggr_packet(int buff_pos, int packet_len,
-                                      __be16 tvlv_len)
+static bool
+batadv_iv_ogm_aggr_packet(int buff_pos, int packet_len,
+                          const struct batadv_ogm_packet *ogm_packet)
 {
         int next_buff_pos = 0;
 
-        next_buff_pos += buff_pos + BATADV_OGM_HLEN;
-        next_buff_pos += ntohs(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;
+
+        /* check if there is enough space for the optional TVLV */
+        next_buff_pos += ntohs(ogm_packet->tvlv_len);
 
         return (next_buff_pos <= packet_len) &&
                (next_buff_pos <= BATADV_MAX_AGGREGATION_BYTES);
@@ -315,7 +321,7 @@ static void batadv_iv_ogm_send_to_if(struct batadv_forw_packet *forw_packet,
 
         /* adjust all flags and log packets */
         while (batadv_iv_ogm_aggr_packet(buff_pos, forw_packet->packet_len,
-                                         batadv_ogm_packet->tvlv_len)) {
+                                         batadv_ogm_packet)) {
                 /* we might have aggregated direct link packets with an
                  * ordinary base packet
                  */
@@ -1704,7 +1710,7 @@ static int batadv_iv_ogm_receive(struct sk_buff *skb,
 
         /* unpack the aggregated packets and process them one by one */
         while (batadv_iv_ogm_aggr_packet(ogm_offset, skb_headlen(skb),
-                                         ogm_packet->tvlv_len)) {
+                                         ogm_packet)) {
                 batadv_iv_ogm_process(skb, ogm_offset, if_incoming);
 
                 ogm_offset += BATADV_OGM_HLEN;