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Date: Sun, 24 Oct 2010 16:27:10 +0200
From: Eric Dumazet <eric.dumazet@...il.com>
To: David Miller <davem@...emloft.net>
Cc: netdev <netdev@...r.kernel.org>,
Johannes Berg <johannes@...solutions.net>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: [PATCH] netlink: fix netlink_change_ngroups()
commit 6c04bb18ddd633 (netlink: use call_rcu for netlink_change_ngroups)
used a somewhat convoluted and racy way to perform call_rcu().
The old block of memory is freed after a grace period, but the rcu_head
used to track it is located in new block.
This can clash if we call two times or more netlink_change_ngroups(),
and a block is freed before another. call_rcu() called on different cpus
makes no guarantee in order of callbacks.
Fix this using a more standard way of handling this : Each block of
memory contains its own rcu_head, so that no 'use after free' can
happens.
Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>
CC: Johannes Berg <johannes@...solutions.net>
CC: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
---
net/netlink/af_netlink.c | 65 +++++++++++++------------------------
1 files changed, 24 insertions(+), 41 deletions(-)
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index cd96ed3..478181d 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -83,9 +83,9 @@ struct netlink_sock {
struct module *module;
};
-struct listeners_rcu_head {
- struct rcu_head rcu_head;
- void *ptr;
+struct listeners {
+ struct rcu_head rcu;
+ unsigned long masks[0];
};
#define NETLINK_KERNEL_SOCKET 0x1
@@ -119,7 +119,7 @@ struct nl_pid_hash {
struct netlink_table {
struct nl_pid_hash hash;
struct hlist_head mc_list;
- unsigned long *listeners;
+ struct listeners __rcu *listeners;
unsigned int nl_nonroot;
unsigned int groups;
struct mutex *cb_mutex;
@@ -338,7 +338,7 @@ netlink_update_listeners(struct sock *sk)
if (i < NLGRPLONGS(nlk_sk(sk)->ngroups))
mask |= nlk_sk(sk)->groups[i];
}
- tbl->listeners[i] = mask;
+ tbl->listeners->masks[i] = mask;
}
/* this function is only called with the netlink table "grabbed", which
* makes sure updates are visible before bind or setsockopt return. */
@@ -936,7 +936,7 @@ EXPORT_SYMBOL(netlink_unicast);
int netlink_has_listeners(struct sock *sk, unsigned int group)
{
int res = 0;
- unsigned long *listeners;
+ struct listeners *listeners;
BUG_ON(!netlink_is_kernel(sk));
@@ -944,7 +944,7 @@ int netlink_has_listeners(struct sock *sk, unsigned int group)
listeners = rcu_dereference(nl_table[sk->sk_protocol].listeners);
if (group - 1 < nl_table[sk->sk_protocol].groups)
- res = test_bit(group - 1, listeners);
+ res = test_bit(group - 1, listeners->masks);
rcu_read_unlock();
@@ -1498,7 +1498,7 @@ netlink_kernel_create(struct net *net, int unit, unsigned int groups,
struct socket *sock;
struct sock *sk;
struct netlink_sock *nlk;
- unsigned long *listeners = NULL;
+ struct listeners *listeners = NULL;
BUG_ON(!nl_table);
@@ -1523,8 +1523,7 @@ netlink_kernel_create(struct net *net, int unit, unsigned int groups,
if (groups < 32)
groups = 32;
- listeners = kzalloc(NLGRPSZ(groups) + sizeof(struct listeners_rcu_head),
- GFP_KERNEL);
+ listeners = kzalloc(sizeof(*listeners) + NLGRPSZ(groups), GFP_KERNEL);
if (!listeners)
goto out_sock_release;
@@ -1541,7 +1540,7 @@ netlink_kernel_create(struct net *net, int unit, unsigned int groups,
netlink_table_grab();
if (!nl_table[unit].registered) {
nl_table[unit].groups = groups;
- nl_table[unit].listeners = listeners;
+ rcu_assign_pointer(nl_table[unit].listeners, listeners);
nl_table[unit].cb_mutex = cb_mutex;
nl_table[unit].module = module;
nl_table[unit].registered = 1;
@@ -1572,43 +1571,28 @@ netlink_kernel_release(struct sock *sk)
EXPORT_SYMBOL(netlink_kernel_release);
-static void netlink_free_old_listeners(struct rcu_head *rcu_head)
+static void listeners_free_rcu(struct rcu_head *head)
{
- struct listeners_rcu_head *lrh;
-
- lrh = container_of(rcu_head, struct listeners_rcu_head, rcu_head);
- kfree(lrh->ptr);
+ kfree(container_of(head, struct listeners, rcu));
}
int __netlink_change_ngroups(struct sock *sk, unsigned int groups)
{
- unsigned long *listeners, *old = NULL;
- struct listeners_rcu_head *old_rcu_head;
+ struct listeners *new, *old;
struct netlink_table *tbl = &nl_table[sk->sk_protocol];
if (groups < 32)
groups = 32;
if (NLGRPSZ(tbl->groups) < NLGRPSZ(groups)) {
- listeners = kzalloc(NLGRPSZ(groups) +
- sizeof(struct listeners_rcu_head),
- GFP_ATOMIC);
- if (!listeners)
+ new = kzalloc(sizeof(*new) + NLGRPSZ(groups), GFP_ATOMIC);
+ if (!new)
return -ENOMEM;
- old = tbl->listeners;
- memcpy(listeners, old, NLGRPSZ(tbl->groups));
- rcu_assign_pointer(tbl->listeners, listeners);
- /*
- * Free the old memory after an RCU grace period so we
- * don't leak it. We use call_rcu() here in order to be
- * able to call this function from atomic contexts. The
- * allocation of this memory will have reserved enough
- * space for struct listeners_rcu_head at the end.
- */
- old_rcu_head = (void *)(tbl->listeners +
- NLGRPLONGS(tbl->groups));
- old_rcu_head->ptr = old;
- call_rcu(&old_rcu_head->rcu_head, netlink_free_old_listeners);
+ old = rcu_dereference_raw(tbl->listeners);
+ memcpy(new->masks, old->masks, NLGRPSZ(tbl->groups));
+ rcu_assign_pointer(tbl->listeners, new);
+
+ call_rcu(&old->rcu, listeners_free_rcu);
}
tbl->groups = groups;
@@ -2104,18 +2088,17 @@ static void __net_exit netlink_net_exit(struct net *net)
static void __init netlink_add_usersock_entry(void)
{
- unsigned long *listeners;
+ struct listeners *listeners;
int groups = 32;
- listeners = kzalloc(NLGRPSZ(groups) + sizeof(struct listeners_rcu_head),
- GFP_KERNEL);
+ listeners = kzalloc(sizeof(*listeners) + NLGRPSZ(groups), GFP_KERNEL);
if (!listeners)
- panic("netlink_add_usersock_entry: Cannot allocate listneres\n");
+ panic("netlink_add_usersock_entry: Cannot allocate listeners\n");
netlink_table_grab();
nl_table[NETLINK_USERSOCK].groups = groups;
- nl_table[NETLINK_USERSOCK].listeners = listeners;
+ rcu_assign_pointer(nl_table[NETLINK_USERSOCK].listeners, listeners);
nl_table[NETLINK_USERSOCK].module = THIS_MODULE;
nl_table[NETLINK_USERSOCK].registered = 1;
--
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