[PATCH batadv v2 5/5] batman-adv: annotate functions which may reallocate the skbuff

When a function is called which reallocated the skbuff, it is necessary to
reacquire the pointers into the skb data. Otherwise they might cause an
use-after-free.

But is hard to identify such case when it is not clear that helpers are
actually using skb-reallocating functions.

Signed-off-by: Sven Eckelmann <[email protected]>
---
 net/batman-adv/bridge_loop_avoidance.c | 10 +++++++++
 net/batman-adv/distributed-arp-table.c | 40 ++++++++++++++++++++++++++++++++++
 net/batman-adv/gateway_client.c        |  6 ++++-
 net/batman-adv/main.c                  |  5 +++++
 net/batman-adv/routing.c               |  5 +++++
 5 files changed, 65 insertions(+), 1 deletion(-)

diff --git a/net/batman-adv/bridge_loop_avoidance.c b/net/batman-adv/bridge_loop_avoidance.c
index fe2618b5..bf9593ca 100644
--- a/net/batman-adv/bridge_loop_avoidance.c
+++ b/net/batman-adv/bridge_loop_avoidance.c
@@ -1087,6 +1087,11 @@ static int batadv_check_claim_group(struct batadv_priv *bat_priv,
  * @primary_if: the primary hard interface of this batman mesh interface
  * @skb: the frame to be checked
  *
+ * Warning: This function may reallocate the skb data buffer via
+ * batadv_get_vid(). Any pointer into the skb data (e.g. obtained
+ * from skb->data or eth_hdr()) before this call must be considered
+ * invalid afterwards and has to be reacquired.
+ *
  * Return: true if it was a claim frame, otherwise return false to
  * tell the callee that it can use the frame on its own.
  */
@@ -1820,6 +1825,11 @@ bool batadv_bla_is_backbone_gw_orig(struct batadv_priv *bat_priv, u8 *orig,
  * @orig_node: the orig_node of the frame
  * @hdr_size: maximum length of the frame
  *
+ * Warning: This function may reallocate the skb data buffer via
+ * pskb_may_pull() and batadv_get_vid(). Any pointer into the skb data (e.g.
+ * obtained from skb->data or eth_hdr()) before this call must be considered
+ * invalid afterwards and has to be reacquired.
+ *
  * Return: true if the orig_node is also a gateway on the mesh interface,
  * otherwise it returns false.
  */
diff --git a/net/batman-adv/distributed-arp-table.c b/net/batman-adv/distributed-arp-table.c
index 7221d569..f1066db8 100644
--- a/net/batman-adv/distributed-arp-table.c
+++ b/net/batman-adv/distributed-arp-table.c
@@ -1064,6 +1064,11 @@ int batadv_dat_cache_dump(struct sk_buff *msg, struct netlink_callback *cb)
  * @skb: packet to analyse
  * @hdr_size: size of the possible header before the ARP packet in the skb
  *
+ * Warning: This function may reallocate the skb data buffer via
+ * pskb_may_pull(). Any pointer into the skb data (e.g. obtained from skb->data
+ * or eth_hdr()) before this call must be considered invalid afterwards and has
+ * to be reacquired.
+ *
  * Return: the ARP type if the skb contains a valid ARP packet, 0 otherwise.
  */
 static u16 batadv_arp_get_type(struct batadv_priv *bat_priv,
@@ -1139,6 +1144,11 @@ static u16 batadv_arp_get_type(struct batadv_priv *bat_priv,
  * @skb: the buffer containing the packet to extract the VID from
  * @hdr_size: the size of the batman-adv header encapsulating the packet
  *
+ * Warning: This function calls batadv_get_vid() and may therefore reallocate
+ * the skb data buffer. Any pointer into the skb data (e.g. obtained from
+ * skb->data or eth_hdr()) before this call must be considered invalid
+ * afterwards and has to be reacquired.
+ *
  * Return: If the packet embedded in the skb is vlan tagged this function
  * returns the VID with the BATADV_VLAN_HAS_TAG flag. Otherwise BATADV_NO_FLAGS
  * is returned.
@@ -1201,6 +1211,11 @@ batadv_dat_arp_create_reply(struct batadv_priv *bat_priv, __be32 ip_src,
  * @bat_priv: the bat priv with all the mesh interface information
  * @skb: packet to check
  *
+ * Warning: This function may reallocate the skb data buffer via
+ * batadv_dat_get_vid(). Any pointer into the skb data (e.g. obtained
+ * from skb->data or eth_hdr()) before this call must be considered
+ * invalid afterwards and has to be reacquired.
+ *
  * Return: true if the message has been sent to the dht candidates, false
  * otherwise. In case of a positive return value the message has to be enqueued
  * to permit the fallback.
@@ -1300,6 +1315,11 @@ bool batadv_dat_snoop_outgoing_arp_request(struct batadv_priv *bat_priv,
  * @skb: packet to check
  * @hdr_size: size of the encapsulation header
  *
+ * Warning: This function may reallocate the skb data buffer via
+ * batadv_dat_get_vid(). Any pointer into the skb data (e.g. obtained
+ * from skb->data or eth_hdr()) before this call must be considered
+ * invalid afterwards and has to be reacquired.
+ *
  * Return: true if the request has been answered, false otherwise.
  */
 bool batadv_dat_snoop_incoming_arp_request(struct batadv_priv *bat_priv,
@@ -1367,6 +1387,11 @@ bool batadv_dat_snoop_incoming_arp_request(struct batadv_priv *bat_priv,
  * batadv_dat_snoop_outgoing_arp_reply() - snoop the ARP reply and fill the DHT
  * @bat_priv: the bat priv with all the mesh interface information
  * @skb: packet to check
+ *
+ * Warning: This function may reallocate the skb data buffer via
+ * batadv_dat_get_vid(). Any pointer into the skb data (e.g. obtained
+ * from skb->data or eth_hdr()) before this call must be considered
+ * invalid afterwards and has to be reacquired.
  */
 void batadv_dat_snoop_outgoing_arp_reply(struct batadv_priv *bat_priv,
 					 struct sk_buff *skb)
@@ -1414,6 +1439,11 @@ void batadv_dat_snoop_outgoing_arp_reply(struct batadv_priv *bat_priv,
  * @skb: packet to check
  * @hdr_size: size of the encapsulation header
  *
+ * Warning: This function may reallocate the skb data buffer via
+ * batadv_dat_get_vid(). Any pointer into the skb data (e.g. obtained
+ * from skb->data or eth_hdr()) before this call must be considered
+ * invalid afterwards and has to be reacquired.
+ *
  * Return: true if the packet was snooped and consumed by DAT. False if the
  * packet has to be delivered to the interface
  */
@@ -1817,6 +1847,11 @@ void batadv_dat_snoop_outgoing_dhcp_ack(struct batadv_priv *bat_priv,
  * This function first checks whether the given skb is a valid DHCPACK. If
  * so then its source MAC and IP as well as its DHCP Client Hardware Address
  * field and DHCP Your IP Address field are added to the local DAT cache.
+ *
+ * Warning: This function may reallocate the skb data buffer via
+ * pskb_may_pull()/batadv_dat_get_vid(). Any pointer into the skb data (e.g.
+ * obtained from skb->data or eth_hdr()) before this call must be considered
+ * invalid afterwards and has to be reacquired.
  */
 void batadv_dat_snoop_incoming_dhcp_ack(struct batadv_priv *bat_priv,
 					struct sk_buff *skb, int hdr_size)
@@ -1865,6 +1900,11 @@ void batadv_dat_snoop_incoming_dhcp_ack(struct batadv_priv *bat_priv,
  * @bat_priv: the bat priv with all the mesh interface information
  * @forw_packet: the broadcast packet
  *
+ * Warning: This function may reallocate the skb data buffer via
+ * batadv_dat_get_vid(). Any pointer into the skb data (e.g. obtained
+ * from skb->data or eth_hdr()) before this call must be considered
+ * invalid afterwards and has to be reacquired.
+ *
  * Return: true if the node can drop the packet, false otherwise.
  */
 bool batadv_dat_drop_broadcast_packet(struct batadv_priv *bat_priv,
diff --git a/net/batman-adv/gateway_client.c b/net/batman-adv/gateway_client.c
index bc69f2ba..0dfbd3f5 100644
--- a/net/batman-adv/gateway_client.c
+++ b/net/batman-adv/gateway_client.c
@@ -679,7 +679,11 @@ batadv_gw_dhcp_recipient_get(struct sk_buff *skb, unsigned int *header_len,
  * server. Due to topology changes it may be the case that the GW server
  * previously selected is not the best one anymore.
  *
- * This call might reallocate skb data.
+ * Warning: This function may reallocate the skb data buffer via
+ * batadv_get_vid(). Any pointer into the skb data (e.g. obtained
+ * from skb->data or eth_hdr()) before this call must be considered
+ * invalid afterwards and has to be reacquired.
+ *
  * Must be invoked only when the DHCP packet is going TO a DHCP SERVER.
  *
  * Return: true if the packet destination is unicast and it is not the best gw,
diff --git a/net/batman-adv/main.c b/net/batman-adv/main.c
index 9a9d882a..95ad4f41 100644
--- a/net/batman-adv/main.c
+++ b/net/batman-adv/main.c
@@ -612,6 +612,11 @@ void batadv_recv_handler_unregister(u8 packet_type)
  * @skb: the buffer containing the packet
  * @header_len: length of the batman header preceding the ethernet header
  *
+ * Warning: This function may reallocate the skb data buffer via
+ * pskb_may_pull(). Any pointer into the skb data (e.g. obtained from skb->data
+ * or eth_hdr()) before this call must be considered invalid afterwards and has
+ * to be reacquired.
+ *
  * Return: VID with the BATADV_VLAN_HAS_TAG flag when the packet embedded in the
  * skb is vlan tagged. Otherwise BATADV_NO_FLAGS.
  */
diff --git a/net/batman-adv/routing.c b/net/batman-adv/routing.c
index 7d9a2b59..cd290a7b 100644
--- a/net/batman-adv/routing.c
+++ b/net/batman-adv/routing.c
@@ -871,6 +871,11 @@ batadv_reroute_unicast_packet(struct batadv_priv *bat_priv, struct sk_buff *skb,
  * @skb: the unicast packet to check
  * @hdr_len: length of the unicast header preceding the payload
  *
+ * Warning: This function may reallocate the skb data buffer via
+ * pskb_may_pull() and batadv_get_vid(). Any pointer into the skb data (e.g.
+ * obtained from skb->data or eth_hdr()) before this call must be considered
+ * invalid afterwards and has to be reacquired.
+ *
  * Return: true if the packet may be processed further, false if it has been
  *  consumed or has to be dropped by the caller
  */

-- 
2.47.3