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ip: ip_ra_control() rcu fix 

commit 66018506e1 (ip: Router Alert RCU conversion) introduced RCU
lookups to ip_call_ra_chain(). It missed proper deinit phase :
When ip_ra_control() deletes an ip_ra_chain, it should make sure
ip_call_ra_chain() users can not start to use socket during the rcu
grace period. It should also delay the sock_put() after the grace
period, or we risk a premature socket freeing and corruptions, as
raw sockets are not rcu protected yet.

This delay avoids using expensive atomic_inc_not_zero() in
ip_call_ra_chain().

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2010-06-09 16:21:07 +00:00 committed by David S. Miller
parent 96b52e61be
commit 592fcb9dfa
2 changed files with 19 additions and 5 deletions
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5
include/net/ip.h
View File

@ -61,7 +61,10 @@ struct ipcm_cookie {
struct ip_ra_chain {
struct ip_ra_chain *next;
struct sock *sk;
void (*destructor)(struct sock *);
union {
void (*destructor)(struct sock *);
struct sock *saved_sk;
};
struct rcu_head rcu;
};

19
net/ipv4/ip_sockglue.c
View File

@ -241,9 +241,13 @@ int ip_cmsg_send(struct net *net, struct msghdr *msg, struct ipcm_cookie *ipc)
struct ip_ra_chain *ip_ra_chain;
static DEFINE_SPINLOCK(ip_ra_lock);
static void ip_ra_free_rcu(struct rcu_head *head)
static void ip_ra_destroy_rcu(struct rcu_head *head)
{
kfree(container_of(head, struct ip_ra_chain, rcu));
struct ip_ra_chain *ra = container_of(head, struct ip_ra_chain, rcu);
sock_put(ra->saved_sk);
kfree(ra);
}
int ip_ra_control(struct sock *sk, unsigned char on,
@ -264,13 +268,20 @@ int ip_ra_control(struct sock *sk, unsigned char on,
kfree(new_ra);
return -EADDRINUSE;
}
/* dont let ip_call_ra_chain() use sk again */
ra->sk = NULL;
rcu_assign_pointer(*rap, ra->next);
spin_unlock_bh(&ip_ra_lock);
if (ra->destructor)
ra->destructor(sk);
sock_put(sk);
call_rcu(&ra->rcu, ip_ra_free_rcu);
/*
* Delay sock_put(sk) and kfree(ra) after one rcu grace
* period. This guarantee ip_call_ra_chain() dont need
* to mess with socket refcounts.
*/
ra->saved_sk = sk;
call_rcu(&ra->rcu, ip_ra_destroy_rcu);
return 0;
}
}