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filter: fix sk_filter rcu handling 

Pavel Emelyanov tried to fix a race between sk_filter_(de|at)tach and
sk_clone() in commit 47e958eac2

Problem is we can have several clones sharing a common sk_filter, and
these clones might want to sk_filter_attach() their own filters at the
same time, and can overwrite old_filter->rcu, corrupting RCU queues.

We can not use filter->rcu without being sure no other thread could do
the same thing.

Switch code to a more conventional ref-counting technique : Do the
atomic decrement immediately and queue one rcu call back when last
reference is released.

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 2010-12-06 09:29:43 -08:00 committed by David S. Miller
parent e7dfc8dbdf
commit 46bcf14f44
2 changed files with 9 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
include/net/sock.h
View File

@ -1155,6 +1155,8 @@ extern void sk_common_release(struct sock *sk);
/* Initialise core socket variables */
extern void sock_init_data(struct socket *sock, struct sock *sk);
extern void sk_filter_release_rcu(struct rcu_head *rcu);
/**
* sk_filter_release - release a socket filter
* @fp: filter to remove
@ -1165,7 +1167,7 @@ extern void sock_init_data(struct socket *sock, struct sock *sk);
static inline void sk_filter_release(struct sk_filter *fp)
{
if (atomic_dec_and_test(&fp->refcnt))
kfree(fp);
call_rcu_bh(&fp->rcu, sk_filter_release_rcu);
}
static inline void sk_filter_uncharge(struct sock *sk, struct sk_filter *fp)

19
net/core/filter.c
View File

@ -589,23 +589,16 @@ int sk_chk_filter(struct sock_filter *filter, int flen)
EXPORT_SYMBOL(sk_chk_filter);
/**
* sk_filter_rcu_release - Release a socket filter by rcu_head
* sk_filter_release_rcu - Release a socket filter by rcu_head
* @rcu: rcu_head that contains the sk_filter to free
*/
static void sk_filter_rcu_release(struct rcu_head *rcu)
void sk_filter_release_rcu(struct rcu_head *rcu)
{
struct sk_filter *fp = container_of(rcu, struct sk_filter, rcu);
sk_filter_release(fp);
}
static void sk_filter_delayed_uncharge(struct sock *sk, struct sk_filter *fp)
{
unsigned int size = sk_filter_len(fp);
atomic_sub(size, &sk->sk_omem_alloc);
call_rcu_bh(&fp->rcu, sk_filter_rcu_release);
kfree(fp);
}
EXPORT_SYMBOL(sk_filter_release_rcu);
/**
* sk_attach_filter - attach a socket filter
@ -649,7 +642,7 @@ int sk_attach_filter(struct sock_fprog *fprog, struct sock *sk)
rcu_assign_pointer(sk->sk_filter, fp);
if (old_fp)
sk_filter_delayed_uncharge(sk, old_fp);
sk_filter_uncharge(sk, old_fp);
return 0;
}
EXPORT_SYMBOL_GPL(sk_attach_filter);
@ -663,7 +656,7 @@ int sk_detach_filter(struct sock *sk)
sock_owned_by_user(sk));
if (filter) {
rcu_assign_pointer(sk->sk_filter, NULL);
sk_filter_delayed_uncharge(sk, filter);
sk_filter_uncharge(sk, filter);
ret = 0;
}
return ret;