Commit 6d772ac5 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

netlink: use kfree_rcu() in netlink_release() 



On some suspend/resume operations involving wimax device, we have
noticed some intermittent memory corruptions in netlink code.

Stéphane Marchesin tracked this corruption in netlink_update_listeners()
and suggested a patch.

It appears netlink_release() should use kfree_rcu() instead of kfree()
for the listeners structure as it may be used by other cpus using RCU
protection.

netlink_release() must set to NULL the listeners pointer when
it is about to be freed.

Also have to protect netlink_update_listeners() and
netlink_has_listeners() if listeners is NULL.

Add a nl_deref_protected() lockdep helper to properly document which
locks protects us.

Reported-by: default avatarJonathan Kliegman <kliegs@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Stéphane Marchesin <marcheu@google.com>
Cc: Sam Leffler <sleffler@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 13d82bf5

net/netlink/af_netlink.c

+15 −4
Original line number Diff line number Diff line
@@ -138,6 +138,8 @@ static int netlink_dump(struct sock *sk); 
static DEFINE_RWLOCK(nl_table_lock);

static atomic_t nl_table_users = ATOMIC_INIT(0);



#define nl_deref_protected(X) rcu_dereference_protected(X, lockdep_is_held(&nl_table_lock));



static ATOMIC_NOTIFIER_HEAD(netlink_chain);



static inline u32 netlink_group_mask(u32 group)
@@ -345,6 +347,11 @@ netlink_update_listeners(struct sock *sk) 
	struct hlist_node *node;

	unsigned long mask;

	unsigned int i;

	struct listeners *listeners;



	listeners = nl_deref_protected(tbl->listeners);

	if (!listeners)

		return;



	for (i = 0; i < NLGRPLONGS(tbl->groups); i++) {

		mask = 0;
@@ -352,7 +359,7 @@ netlink_update_listeners(struct sock *sk) 
			if (i < NLGRPLONGS(nlk_sk(sk)->ngroups))

				mask |= nlk_sk(sk)->groups[i];

		}

		tbl->listeners->masks[i] = mask;

		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. */
@@ -536,7 +543,11 @@ static int netlink_release(struct socket *sock) 
	if (netlink_is_kernel(sk)) {

		BUG_ON(nl_table[sk->sk_protocol].registered == 0);

		if (--nl_table[sk->sk_protocol].registered == 0) {

			kfree(nl_table[sk->sk_protocol].listeners);

			struct listeners *old;



			old = nl_deref_protected(nl_table[sk->sk_protocol].listeners);

			RCU_INIT_POINTER(nl_table[sk->sk_protocol].listeners, NULL);

			kfree_rcu(old, rcu);

			nl_table[sk->sk_protocol].module = NULL;

			nl_table[sk->sk_protocol].bind = NULL;

			nl_table[sk->sk_protocol].flags = 0;
@@ -982,7 +993,7 @@ int netlink_has_listeners(struct sock *sk, unsigned int group) 
	rcu_read_lock();

	listeners = rcu_dereference(nl_table[sk->sk_protocol].listeners);



	if (group - 1 < nl_table[sk->sk_protocol].groups)

	if (listeners && group - 1 < nl_table[sk->sk_protocol].groups)

		res = test_bit(group - 1, listeners->masks);



	rcu_read_unlock();
@@ -1625,7 +1636,7 @@ int __netlink_change_ngroups(struct sock *sk, unsigned int groups) 
		new = kzalloc(sizeof(*new) + NLGRPSZ(groups), GFP_ATOMIC);

		if (!new)

			return -ENOMEM;

		old = rcu_dereference_protected(tbl->listeners, 1);

		old = nl_deref_protected(tbl->listeners);

		memcpy(new->masks, old->masks, NLGRPSZ(tbl->groups));

		rcu_assign_pointer(tbl->listeners, new);

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