diff mbox

[maint,2/2] batman-adv: Fix potential synchronization issues in mcast tvlv handler

Message ID 1434349345-12854-3-git-send-email-linus.luessing@c0d3.blue
State Superseded, archived
Headers show

Commit Message

Linus Lüssing June 15, 2015, 6:22 a.m. UTC
So far the mcast tvlv handler did not anticipate the processing of
multiple incoming OGMs from the same originator at the same time. This
can lead to various issues:

* Broken refcounting: For instance two mcast handlers might both assume
  that an originator just got multicast capabilities and will together
  wrongly decrease mcast.num_disabled by two, potentially leading to
  an integer underflow.

* Potential kernel panic on hlist_del_rcu(): Two mcast handlers might
  one after another try to do an
  hlist_del_rcu(&orig->mcast_want_all_*_node). The second one will
  cause memory corruption / crashes.
  (Reported by: Sven Eckelmann <sven@narfation.org>)

Right in the beginning the code path makes assumptions about the current
multicast related state of an originator and bases all updates on that. The
easiest and least error prune way to fix the issues in this case is to
serialize multiple mcast handler invocations with a spinlock.

Fixes: 77ec494490d6 ("batman-adv: Announce new capability via multicast TVLV")
Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
---
 multicast.c  |    2 ++
 originator.c |    1 +
 types.h      |    2 ++
 3 files changed, 5 insertions(+)

Comments

Marek Lindner June 16, 2015, 7:07 a.m. UTC | #1
On Monday, June 15, 2015 08:22:25 Linus Lüssing wrote:
> So far the mcast tvlv handler did not anticipate the processing of
> multiple incoming OGMs from the same originator at the same time. This
> can lead to various issues:
> 
> * Broken refcounting: For instance two mcast handlers might both assume
>   that an originator just got multicast capabilities and will together
>   wrongly decrease mcast.num_disabled by two, potentially leading to
>   an integer underflow.
> 
> * Potential kernel panic on hlist_del_rcu(): Two mcast handlers might
>   one after another try to do an
>   hlist_del_rcu(&orig->mcast_want_all_*_node). The second one will
>   cause memory corruption / crashes.
>   (Reported by: Sven Eckelmann <sven@narfation.org>)

As far as I can tell from looking at the code your patch does not address the 
issue raised by Sven.

The first problem is that the mcast code calls hlist_del_rcu() without 
verifying whether or not the element is still in the list. Adding a spinlock 
is not going to change that. You can still have a purge event going on while 
we just receive a new OGM because the purge caller does not need to hold the 
newly added lock.

Cheers,
Marek
diff mbox

Patch

diff --git a/multicast.c b/multicast.c
index 00612bf..e6db978 100644
--- a/multicast.c
+++ b/multicast.c
@@ -674,6 +674,7 @@  static void batadv_mcast_tvlv_ogm_handler_v1(struct batadv_priv *bat_priv,
 	uint8_t mcast_flags = BATADV_NO_FLAGS;
 	bool orig_initialized;
 
+	spin_lock_bh(&orig->mcast_handler_lock);
 	orig_initialized = orig->capa_initialized & BATADV_ORIG_CAPA_HAS_MCAST;
 
 	/* If mcast support is turned on decrease the disabled mcast node
@@ -707,6 +708,7 @@  static void batadv_mcast_tvlv_ogm_handler_v1(struct batadv_priv *bat_priv,
 	batadv_mcast_want_ipv6_update(bat_priv, orig, mcast_flags);
 
 	orig->mcast_flags = mcast_flags;
+	spin_unlock_bh(&orig->mcast_handler_lock);
 }
 
 /**
diff --git a/originator.c b/originator.c
index e3900e4..78c027d 100644
--- a/originator.c
+++ b/originator.c
@@ -663,6 +663,7 @@  struct batadv_orig_node *batadv_orig_node_new(struct batadv_priv *bat_priv,
 	spin_lock_init(&orig_node->tt_buff_lock);
 	spin_lock_init(&orig_node->tt_lock);
 	spin_lock_init(&orig_node->vlan_list_lock);
+	spin_lock_init(&orig_node->mcast_handler_lock);
 
 	batadv_nc_init_orig(orig_node);
 
diff --git a/types.h b/types.h
index c6ec558..1d800c5 100644
--- a/types.h
+++ b/types.h
@@ -251,6 +251,8 @@  struct batadv_orig_node {
 	unsigned long last_seen;
 	unsigned long bcast_seqno_reset;
 #ifdef CONFIG_BATMAN_ADV_MCAST
+	/* synchronizes mcast tvlv specific orig changes */
+	spinlock_t mcast_handler_lock;
 	uint8_t mcast_flags;
 	struct hlist_node mcast_want_all_unsnoopables_node;
 	struct hlist_node mcast_want_all_ipv4_node;