[PATCH v2 1/2] batman-adv: Only read OGM tvlv_len after buffer len check

[PATCH v2 1/2] batman-adv: Only read OGM tvlv_len after buffer len check

[Sven Eckelmann]

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: 0b6aa0d43767 ("batman-adv: tvlv - basic infrastructure")
Reported-by: syzbot+355cab184197dbbfa384@syzkaller.appspotmail.com
Signed-off-by: Sven Eckelmann <sven@narfation.org>
---
v2:

* change __be16 pointer parameter to const const struct batadv_ogm_packet

 net/batman-adv/bat_iv_ogm.c | 20 +++++++++++++-------
 1 file changed, 13 insertions(+), 7 deletions(-)

diff --git a/net/batman-adv/bat_iv_ogm.c b/net/batman-adv/bat_iv_ogm.c
index 240ed709..d78938e3 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;
-- 
2.20.1

[PATCH v2 2/2] batman-adv: Only read OGM2 tvlv_len after buffer len check

[Sven Eckelmann]

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: 667996ebeab4 ("batman-adv: OGMv2 - implement originators logic")
Signed-off-by: Sven Eckelmann <sven@narfation.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 319249f0..dc4f7430 100644
--- a/net/batman-adv/bat_v_ogm.c
+++ b/net/batman-adv/bat_v_ogm.c
@@ -806,17 +806,23 @@ 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);
@@ -993,7 +999,7 @@ 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

Re: [PATCH v2 1/2] batman-adv: Only read OGM tvlv_len after buffer len check

[Antonio Quartulli]

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Hi,

On 23/08/2019 14:34, Sven Eckelmann wrote:
> 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: 0b6aa0d43767 ("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>

-- 
Antonio Quartulli


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