Before/while a tracker packet is being searched for next hops for its destination entries, it will also be checked if the number of destination and mcast entries might exceed the tracker_packet_len. Otherwise we might read/write in unallocated memory. Such a broken tracker packet could potentially occure when we are going to reuse route_mcast_tracker_packet for tracker packets received from a neighbour node.
In such a case, we are just reducing the stated mcast / dest numbers in the tracker packet to fit the size of the allocated buffer.
Signed-off-by: Linus Lüssing linus.luessing@saxnet.de --- multicast.c | 27 ++++++++++++++++++++++++--- 1 files changed, 24 insertions(+), 3 deletions(-)
diff --git a/batman-adv/multicast.c b/batman-adv/multicast.c index 34e89a8..c06035f 100644 --- a/batman-adv/multicast.c +++ b/batman-adv/multicast.c @@ -366,17 +366,38 @@ free: return 1; }
-/* Collect nexthops for all dest entries specified in this tracker packet */ +/* Collect nexthops for all dest entries specified in this tracker packet. + * It also reduces the number of elements in the tracker packet if they exceed + * the buffers length (e.g. because of a received, broken tracker packet) to + * avoid writing in unallocated memory. */ static int tracker_next_hops(struct mcast_tracker_packet *tracker_packet, + int tracker_packet_len, struct dest_entries_list *next_hops, struct bat_priv *bat_priv) { int num_next_hops = 0, ret; struct tracker_packet_state state; + uint8_t *tail = (uint8_t *)tracker_packet + tracker_packet_len;
INIT_LIST_HEAD(&next_hops->list);
tracker_packet_for_each_dest(&state, tracker_packet) { + /* avoid writing outside of unallocated memory later */ + if (state.dest_entry + ETH_ALEN > tail) { + bat_dbg(DBG_BATMAN, bat_priv, + "mcast tracker packet is broken, too many " + "entries claimed for its length, repairing"); + + tracker_packet->num_mcast_entries = state.mcast_num; + + if (state.dest_num) { + tracker_packet->num_mcast_entries++; + state.mcast_entry->num_dest = state.dest_num; + } + + break; + } + ret = add_router_of_dest(next_hops, state.dest_entry, bat_priv); if (!ret) @@ -528,8 +549,8 @@ void route_mcast_tracker_packet( int *tracker_packet_lengths;
rcu_read_lock(); - num_next_hops = tracker_next_hops(tracker_packet, &next_hops, - bat_priv); + num_next_hops = tracker_next_hops(tracker_packet, tracker_packet_len, + &next_hops, bat_priv); if (!num_next_hops) goto out; next_hop_tracker_packets = kmalloc(tracker_packet_len * num_next_hops,