[PATCH 4.19 43/79] batman-adv: Only read OGM2 tvlv_len after buffer len check

Greg Kroah-Hartman
2019-09-19T22:15:04Z

From: Sven Eckelmann <sven@narfation.org>

[ Upstream commit 0ff0f15a32c093381ad1abc06abe85afb561ab28 ]

Multiple batadv_ogm2_packet can be stored in an skbuff. The functions
batadv_v_ogm_send_to_if() uses batadv_v_ogm_aggr_packet() to check if there
is another additional batadv_ogm2_packet in the skb or not before they
continue processing the packet.

The length for such an OGM2 is BATADV_OGM2_HLEN +
batadv_ogm2_packet->tvlv_len. The check must first check that at least
BATADV_OGM2_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: 9323158ef9f4 ("batman-adv: OGMv2 - implement originators logic")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/batman-adv/bat_v_ogm.c | 18 ++++++++++++------
1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/net/batman-adv/bat_v_ogm.c b/net/batman-adv/bat_v_ogm.c
index 2948b41b06d47..d241ccc0ca027 100644
--- a/net/batman-adv/bat_v_ogm.c
+++ b/net/batman-adv/bat_v_ogm.c
@@ -643,17 +643,23 @@ batadv_v_ogm_process_per_outif(struct batadv_priv *bat_priv,
* batadv_v_ogm_aggr_packet() - checks if there is another OGM aggregated
* @buff_pos: current position in the skb
* @packet_len: total length of the skb
- * @tvlv_len: tvlv length of the previously considered OGM
+ * @ogm2_packet: potential OGM2 in buffer
*
* Return: true if there is enough space for another OGM, false otherwise.
*/
-static bool batadv_v_ogm_aggr_packet(int buff_pos, int packet_len,
- __be16 tvlv_len)
+static bool
+batadv_v_ogm_aggr_packet(int buff_pos, int packet_len,
+ const struct batadv_ogm2_packet *ogm2_packet)
{
int next_buff_pos = 0;

- next_buff_pos += buff_pos + BATADV_OGM2_HLEN;
- next_buff_pos += ntohs(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;
+
+ /* check if there is enough space for the optional TVLV */
+ next_buff_pos += ntohs(ogm2_packet->tvlv_len);

return (next_buff_pos <= packet_len) &&
(next_buff_pos <= BATADV_MAX_AGGREGATION_BYTES);
@@ -830,7 +836,7 @@ int batadv_v_ogm_packet_recv(struct sk_buff *skb,
ogm_packet = (struct batadv_ogm2_packet *)skb->data;

while (batadv_v_ogm_aggr_packet(ogm_offset, skb_headlen(skb),
- ogm_packet->tvlv_len)) {
+ ogm_packet)) {
batadv_v_ogm_process(skb, ogm_offset, if_incoming);

ogm_offset += BATADV_OGM2_HLEN;
--
2.20.1