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

commit a15d56a60760aa9dbe26343b9a0ac5228f35d445 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/net/batman-adv/bat_iv_ogm.c b/net/batman-adv/bat_iv_ogm.c
index 1ae8c59..780700f 100644 (file)
--- a/net/batman-adv/bat_iv_ogm.c
+++ b/net/batman-adv/bat_iv_ogm.c
@@ -450,17 +450,23 @@ 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);
@@ -488,7 +494,7 @@ 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
                 */
@@ -1841,7 +1847,7 @@ 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;