The update critical sections of if_list must be protected by a locking primitive other than RCU. The iterator must also be protected by the chosen locking mechanism.

The rtnl_lock in hardif_remove_interfaces must also be moved outside the iterator primitive to ensure that we don't deadlock the kernel due to differently nested locks in hardif_remove_interfaces and hard_if_event.

Signed-off-by: Sven Eckelmann sven.eckelmann@gmx.de --- batman-adv/hard-interface.c | 17 +++++++++++++++-- 1 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/batman-adv/hard-interface.c b/batman-adv/hard-interface.c index edbfddf..3cd7cb1 100644 --- a/batman-adv/hard-interface.c +++ b/batman-adv/hard-interface.c @@ -35,6 +35,9 @@

#define MIN(x, y) ((x) < (y) ? (x) : (y))

+/* protect update critical side of if_list - but not the content */ +static DEFINE_SPINLOCK(if_list_lock); + struct batman_if *get_batman_if_by_netdev(struct net_device *net_dev) { struct batman_if *batman_if; @@ -402,7 +405,11 @@ static struct batman_if *hardif_add_interface(struct net_device *net_dev) INIT_LIST_HEAD(&batman_if->list);

check_known_mac_addr(batman_if->net_dev->dev_addr); + + spin_lock(&if_list_lock); list_add_tail_rcu(&batman_if->list, &if_list); + spin_unlock(&if_list_lock); + return batman_if;

free_if: @@ -430,6 +437,8 @@ static void hardif_remove_interface(struct batman_if *batman_if) return;

batman_if->if_status = IF_TO_BE_REMOVED; + + /* caller must take if_list_lock */ list_del_rcu(&batman_if->list); sysfs_del_hardif(&batman_if->hardif_obj); dev_put(batman_if->net_dev); @@ -440,11 +449,13 @@ void hardif_remove_interfaces(void) { struct batman_if *batman_if, *batman_if_tmp;

+ rtnl_lock(); + spin_lock(&if_list_lock); list_for_each_entry_safe(batman_if, batman_if_tmp, &if_list, list) { - rtnl_lock(); hardif_remove_interface(batman_if); - rtnl_unlock(); } + spin_unlock(&if_list_lock); + rtnl_unlock(); }

static int hard_if_event(struct notifier_block *this, @@ -469,7 +480,9 @@ static int hard_if_event(struct notifier_block *this, hardif_deactivate_interface(batman_if); break; case NETDEV_UNREGISTER: + spin_lock(&if_list_lock); hardif_remove_interface(batman_if); + spin_unlock(&if_list_lock); break; case NETDEV_CHANGEMTU: if (batman_if->soft_iface)

receive_bat_packet is not called with rcu_read_lock so we must ensure by ourself that we protect list_for_each_entry_rcu using the correct RCU locks.

Signed-off-by: Sven Eckelmann sven.eckelmann@gmx.de --- batman-adv/routing.c | 2 ++ 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/batman-adv/routing.c b/batman-adv/routing.c index 603a932..1781b7e 100644 --- a/batman-adv/routing.c +++ b/batman-adv/routing.c @@ -575,6 +575,7 @@ void receive_bat_packet(struct ethhdr *ethhdr, batman_packet->tq, batman_packet->ttl, batman_packet->version, has_directlink_flag);

+ rcu_read_lock(); list_for_each_entry_rcu(batman_if, &if_list, list) { if (batman_if->if_status != IF_ACTIVE) continue; @@ -597,6 +598,7 @@ void receive_bat_packet(struct ethhdr *ethhdr, if (compare_orig(ethhdr->h_source, broadcast_addr)) is_broadcast = 1; } + rcu_read_unlock();

if (batman_packet->version != COMPAT_VERSION) { bat_dbg(DBG_BATMAN, bat_priv,

It is recommended [1] to use synchronize_rcu to simplify the code - especially when otherwise extra locking is needed to protect other code from picking stale elements. It also protects us for emitting to many callbacks which may results in OOM conditions.

The only reason not to use it, would be in performance critical sections or when we are not allowed to block.

[1] Documentation/RCU/checklist.txt

Signed-off-by: Sven Eckelmann sven.eckelmann@gmx.de --- batman-adv/gateway_client.c | 12 ++++-------- batman-adv/hard-interface.c | 10 ++-------- batman-adv/types.h | 2 -- 3 files changed, 6 insertions(+), 18 deletions(-)

diff --git a/batman-adv/gateway_client.c b/batman-adv/gateway_client.c index bfac0ff..8bc1cb0 100644 --- a/batman-adv/gateway_client.c +++ b/batman-adv/gateway_client.c @@ -265,12 +265,6 @@ void gw_node_delete(struct bat_priv *bat_priv, struct orig_node *orig_node) return gw_node_update(bat_priv, orig_node, 0); }

-static void gw_node_free(struct rcu_head *rcu) -{ - struct gw_node *gw_node = container_of(rcu, struct gw_node, rcu); - kfree(gw_node); -} - void gw_node_purge_deleted(struct bat_priv *bat_priv) { struct gw_node *gw_node; @@ -286,7 +280,8 @@ void gw_node_purge_deleted(struct bat_priv *bat_priv) (time_after(jiffies, gw_node->deleted + timeout))) {

hlist_del_rcu(&gw_node->list); - call_rcu(&gw_node->rcu, gw_node_free); + synchronize_rcu(); + kfree(gw_node); } }

@@ -304,7 +299,8 @@ void gw_node_list_free(struct bat_priv *bat_priv) hlist_for_each_entry_safe(gw_node, node, node_tmp, &bat_priv->gw_list, list) { hlist_del_rcu(&gw_node->list); - call_rcu(&gw_node->rcu, gw_node_free); + synchronize_rcu(); + kfree(gw_node); }

gw_deselect(bat_priv); diff --git a/batman-adv/hard-interface.c b/batman-adv/hard-interface.c index 3cd7cb1..0b3ee6b 100644 --- a/batman-adv/hard-interface.c +++ b/batman-adv/hard-interface.c @@ -420,13 +420,6 @@ out: return NULL; }

-static void hardif_free_interface(struct rcu_head *rcu) -{ - struct batman_if *batman_if = container_of(rcu, struct batman_if, rcu); - - kfree(batman_if); -} - static void hardif_remove_interface(struct batman_if *batman_if) { /* first deactivate interface */ @@ -440,9 +433,10 @@ static void hardif_remove_interface(struct batman_if *batman_if)

/* caller must take if_list_lock */ list_del_rcu(&batman_if->list); + synchronize_rcu(); sysfs_del_hardif(&batman_if->hardif_obj); dev_put(batman_if->net_dev); - call_rcu(&batman_if->rcu, hardif_free_interface); + kfree(batman_if); }

void hardif_remove_interfaces(void) diff --git a/batman-adv/types.h b/batman-adv/types.h index e7b53a4..1940404 100644 --- a/batman-adv/types.h +++ b/batman-adv/types.h @@ -44,7 +44,6 @@ struct batman_if { unsigned char *packet_buff; int packet_len; struct kobject *hardif_obj; - struct rcu_head rcu; struct packet_type batman_adv_ptype; struct net_device *soft_iface; }; @@ -96,7 +95,6 @@ struct gw_node { struct hlist_node list; struct orig_node *orig_node; unsigned long deleted; - struct rcu_head rcu; };

/**

get_batman_if_by_netdev and get_active_batman_if may leak data from the rcu protected list of interfaces. The rcu protected list of all gateway nodes leaks the actual data outside the read-side critical area. This is not valid as we may free the data using a call_rcu created callback after we unlock using rcu_read_unlock. A workaround is to provide a reference count to be sure that the memory isn't freed to early.

It is currently only to implement the already existing functionality and doesn't provide the full tracking of all usage cases.

Additionally, we must hardif_hold inside the rcu_read_lock()..rcu_read_unlock() before we attach to the structure which "leaks" it. When another function now removed it from its usage context (primary_if, usage on stack, ...) then we must hardif_put it. If it is decremented to zero then we can issue the call_rcu to the freeing function. So "put" is not allowed inside an rcu_read_lock.

Signed-off-by: Sven Eckelmann sven.eckelmann@gmx.de --- batman-adv/hard-interface.c | 5 +++-- batman-adv/hard-interface.h | 13 +++++++++++++ batman-adv/types.h | 1 + 3 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/batman-adv/hard-interface.c b/batman-adv/hard-interface.c index 0b3ee6b..445498c 100644 --- a/batman-adv/hard-interface.c +++ b/batman-adv/hard-interface.c @@ -403,6 +403,8 @@ static struct batman_if *hardif_add_interface(struct net_device *net_dev) batman_if->soft_iface = NULL; batman_if->if_status = IF_NOT_IN_USE; INIT_LIST_HEAD(&batman_if->list); + atomic_set(&batman_if->refcnt, 0); + hardif_hold(batman_if);

check_known_mac_addr(batman_if->net_dev->dev_addr);

@@ -435,8 +437,7 @@ static void hardif_remove_interface(struct batman_if *batman_if) list_del_rcu(&batman_if->list); synchronize_rcu(); sysfs_del_hardif(&batman_if->hardif_obj); - dev_put(batman_if->net_dev); - kfree(batman_if); + hardif_put(batman_if); }

void hardif_remove_interfaces(void) diff --git a/batman-adv/hard-interface.h b/batman-adv/hard-interface.h index 4b49527..d550889 100644 --- a/batman-adv/hard-interface.h +++ b/batman-adv/hard-interface.h @@ -42,4 +42,17 @@ int batman_skb_recv(struct sk_buff *skb, int hardif_min_mtu(struct net_device *soft_iface); void update_min_mtu(struct net_device *soft_iface);

+static inline void hardif_hold(struct batman_if *batman_if) +{ + atomic_inc(&batman_if->refcnt); +} + +static inline void hardif_put(struct batman_if *batman_if) +{ + if (atomic_dec_and_test(&batman_if->refcnt)) { + dev_put(batman_if->net_dev); + kfree(batman_if); + } +} + #endif /* _NET_BATMAN_ADV_HARD_INTERFACE_H_ */ diff --git a/batman-adv/types.h b/batman-adv/types.h index ecc4365..a609100 100644 --- a/batman-adv/types.h +++ b/batman-adv/types.h @@ -44,6 +44,7 @@ struct batman_if { unsigned char *packet_buff; int packet_len; struct kobject *hardif_obj; + atomic_t refcnt; struct packet_type batman_adv_ptype; struct net_device *soft_iface; };

The return of get_batman_if_by_netdev and get_active_batman_if leaks a pointer from the rcu protected list of interfaces. We must protect it to prevent a too early release of the memory. Those functions must increase the reference counter before rcu_read_unlock or it may be to late to prevent a free.

hardif_add_interface must also increase the reference count for the returned batman_if to make the behaviour consistent.

Reported-by: Paul E. McKenney paulmck@linux.vnet.ibm.com Signed-off-by: Sven Eckelmann sven.eckelmann@gmx.de --- batman-adv/bat_sysfs.c | 37 +++++++++++++++++++++++++++---------- batman-adv/hard-interface.c | 29 ++++++++++++++++++++++++----- 2 files changed, 51 insertions(+), 15 deletions(-)

diff --git a/batman-adv/bat_sysfs.c b/batman-adv/bat_sysfs.c index 8e180ba..79090c9 100644 --- a/batman-adv/bat_sysfs.c +++ b/batman-adv/bat_sysfs.c @@ -453,13 +453,17 @@ static ssize_t show_mesh_iface(struct kobject *kobj, struct attribute *attr, struct device *dev = to_dev(kobj->parent); struct net_device *net_dev = to_net_dev(dev); struct batman_if *batman_if = get_batman_if_by_netdev(net_dev); + ssize_t length;

if (!batman_if) return 0;

- return sprintf(buff, "%s\n", - batman_if->if_status == IF_NOT_IN_USE ? - "none" : batman_if->soft_iface->name); + length = sprintf(buff, "%s\n", batman_if->if_status == IF_NOT_IN_USE ? + "none" : batman_if->soft_iface->name); + + hardif_put(batman_if); + + return length; }

static ssize_t store_mesh_iface(struct kobject *kobj, struct attribute *attr, @@ -469,6 +473,7 @@ static ssize_t store_mesh_iface(struct kobject *kobj, struct attribute *attr, struct net_device *net_dev = to_net_dev(dev); struct batman_if *batman_if = get_batman_if_by_netdev(net_dev); int status_tmp = -1; + int ret;

if (!batman_if) return count; @@ -479,6 +484,7 @@ static ssize_t store_mesh_iface(struct kobject *kobj, struct attribute *attr, if (strlen(buff) >= IFNAMSIZ) { pr_err("Invalid parameter for 'mesh_iface' setting received: " "interface name too long '%s'\n", buff); + hardif_put(batman_if); return -EINVAL; }

@@ -488,13 +494,16 @@ static ssize_t store_mesh_iface(struct kobject *kobj, struct attribute *attr, status_tmp = IF_I_WANT_YOU;

if ((batman_if->if_status == status_tmp) || ((batman_if->soft_iface) && - (strncmp(batman_if->soft_iface->name, buff, IFNAMSIZ) == 0))) + (strncmp(batman_if->soft_iface->name, buff, IFNAMSIZ) == 0))) { + hardif_put(batman_if); return count; + }

if (status_tmp == IF_NOT_IN_USE) { rtnl_lock(); hardif_disable_interface(batman_if); rtnl_unlock(); + hardif_put(batman_if); return count; }

@@ -505,7 +514,10 @@ static ssize_t store_mesh_iface(struct kobject *kobj, struct attribute *attr, rtnl_unlock(); }

- return hardif_enable_interface(batman_if, buff); + ret = hardif_enable_interface(batman_if, buff); + hardif_put(batman_if); + + return ret; }

static ssize_t show_iface_status(struct kobject *kobj, struct attribute *attr, @@ -514,23 +526,28 @@ static ssize_t show_iface_status(struct kobject *kobj, struct attribute *attr, struct device *dev = to_dev(kobj->parent); struct net_device *net_dev = to_net_dev(dev); struct batman_if *batman_if = get_batman_if_by_netdev(net_dev); + ssize_t length;

if (!batman_if) return 0;

switch (batman_if->if_status) { case IF_TO_BE_REMOVED: - return sprintf(buff, "disabling\n"); + length = sprintf(buff, "disabling\n"); case IF_INACTIVE: - return sprintf(buff, "inactive\n"); + length = sprintf(buff, "inactive\n"); case IF_ACTIVE: - return sprintf(buff, "active\n"); + length = sprintf(buff, "active\n"); case IF_TO_BE_ACTIVATED: - return sprintf(buff, "enabling\n"); + length = sprintf(buff, "enabling\n"); case IF_NOT_IN_USE: default: - return sprintf(buff, "not in use\n"); + length = sprintf(buff, "not in use\n"); } + + hardif_put(batman_if); + + return length; }

static BAT_ATTR(mesh_iface, S_IRUGO | S_IWUSR, diff --git a/batman-adv/hard-interface.c b/batman-adv/hard-interface.c index 445498c..f519b4b 100644 --- a/batman-adv/hard-interface.c +++ b/batman-adv/hard-interface.c @@ -51,6 +51,9 @@ struct batman_if *get_batman_if_by_netdev(struct net_device *net_dev) batman_if = NULL;

out: + if (batman_if) + hardif_hold(batman_if); + rcu_read_unlock(); return batman_if; } @@ -98,6 +101,9 @@ static struct batman_if *get_active_batman_if(struct net_device *soft_iface) batman_if = NULL;

out: + if (batman_if) + hardif_hold(batman_if); + rcu_read_unlock(); return batman_if; } @@ -294,6 +300,7 @@ int hardif_enable_interface(struct batman_if *batman_if, char *iface_name) batman_if->batman_adv_ptype.type = __constant_htons(ETH_P_BATMAN); batman_if->batman_adv_ptype.func = batman_skb_recv; batman_if->batman_adv_ptype.dev = batman_if->net_dev; + hardif_hold(batman_if); dev_add_pack(&batman_if->batman_adv_ptype);

atomic_set(&batman_if->seqno, 1); @@ -352,13 +359,20 @@ void hardif_disable_interface(struct batman_if *batman_if) bat_info(batman_if->soft_iface, "Removing interface: %s\n", batman_if->net_dev->name); dev_remove_pack(&batman_if->batman_adv_ptype); + hardif_put(batman_if);

bat_priv->num_ifaces--; orig_hash_del_if(batman_if, bat_priv->num_ifaces);

- if (batman_if == bat_priv->primary_if) - set_primary_if(bat_priv, - get_active_batman_if(batman_if->soft_iface)); + if (batman_if == bat_priv->primary_if) { + struct batman_if *new_if; + + new_if = get_active_batman_if(batman_if->soft_iface); + set_primary_if(bat_priv, new_if); + + if (new_if) + hardif_put(new_if); + }

kfree(batman_if->packet_buff); batman_if->packet_buff = NULL; @@ -412,6 +426,8 @@ static struct batman_if *hardif_add_interface(struct net_device *net_dev) list_add_tail_rcu(&batman_if->list, &if_list); spin_unlock(&if_list_lock);

+ /* extra reference for return */ + hardif_hold(batman_if); return batman_if;

free_if: @@ -461,7 +477,7 @@ static int hard_if_event(struct notifier_block *this, struct bat_priv *bat_priv;

if (!batman_if && event == NETDEV_REGISTER) - batman_if = hardif_add_interface(net_dev); + batman_if = hardif_add_interface(net_dev);

if (!batman_if) goto out; @@ -484,8 +500,10 @@ static int hard_if_event(struct notifier_block *this, update_min_mtu(batman_if->soft_iface); break; case NETDEV_CHANGEADDR: - if (batman_if->if_status == IF_NOT_IN_USE) + if (batman_if->if_status == IF_NOT_IN_USE) { + hardif_put(batman_if); goto out; + }

check_known_mac_addr(batman_if->net_dev->dev_addr); update_mac_addresses(batman_if); @@ -497,6 +515,7 @@ static int hard_if_event(struct notifier_block *this, default: break; }; + hardif_put(batman_if);

out: return NOTIFY_DONE;