Commit 34c5bd66 authored Jul 29, 2014 by Pablo Neira Committed by David S. Miller Jul 30, 2014

net: filter: don't release unattached filter through call_rcu()

sk_unattached_filter_destroy() does not always need to release the
filter object via rcu. Since this filter is never attached to the
socket, the caller should be responsible for releasing the filter
in a safe way, which may not necessarily imply rcu.

This is a short summary of clients of this function:

1) xt_bpf.c and cls_bpf.c use the bpf matchers from rules, these rules
are removed from the packet path before the filter is released. Thus,
the framework makes sure the filter is safely removed.

2) In the ppp driver, the ppp_lock ensures serialization between the
xmit and filter attachment/detachment path. This doesn't use rcu
so deferred release via rcu makes no sense.

3) In the isdn/ppp driver, it is called from isdn_ppp_release()
the isdn_ppp_ioctl(). This driver uses mutex and spinlocks, no rcu.
Thus, deferred rcu makes no sense to me either, the deferred releases
may be just masking the effects of wrong locking strategy, which
should be fixed in the driver itself.

4) In the team driver, this is the only place where the rcu
synchronization with unattached filter is used. Therefore, this
patch introduces synchronize_rcu() which is called from the
genetlink path to make sure the filter doesn't go away while packets
are still walking over it. I think we can revisit this once struct
bpf_prog (that only wraps specific bpf code bits) is in place, then
add some specific struct rcu_head in the scope of the team driver if
Jiri thinks this is needed.

Deferred rcu release for unattached filters was originally introduced
in 302d6637 ("filter: Allow to create sk-unattached filters").

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent e10038a8

drivers/net/team/team_mode_loadbalance.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -293,11 +293,15 @@ static int lb_bpf_func_set(struct team team, struct team_gsetter_ctx ctx)
		__fprog_destroy(lb_priv->ex->orig_fprog);
		orig_fp = rcu_dereference_protected(lb_priv->fp,
		lockdep_is_held(&team->lock));
		sk_unattached_filter_destroy(orig_fp);
		}

		rcu_assign_pointer(lb_priv->fp, fp);
		lb_priv->ex->orig_fprog = fprog;

		if (orig_fp) {
		synchronize_rcu();
		sk_unattached_filter_destroy(orig_fp);
		}
		return 0;
		}

net/core/filter.c

+8 −3

Original line number	Diff line number	Diff line
		@@ -841,6 +841,12 @@ static void sk_release_orig_filter(struct sk_filter *fp)
		}
		}

		static void __sk_filter_release(struct sk_filter *fp)
		{
		sk_release_orig_filter(fp);
		sk_filter_free(fp);
		}

		/**
		* sk_filter_release_rcu - Release a socket filter by rcu_head
		* @rcu: rcu_head that contains the sk_filter to free
		@@ -849,8 +855,7 @@ static void sk_filter_release_rcu(struct rcu_head *rcu)
		{
		struct sk_filter *fp = container_of(rcu, struct sk_filter, rcu);

		sk_release_orig_filter(fp);
		sk_filter_free(fp);
		__sk_filter_release(fp);
		}

		/**
		@@ -1050,7 +1055,7 @@ EXPORT_SYMBOL_GPL(sk_unattached_filter_create);

		void sk_unattached_filter_destroy(struct sk_filter *fp)
		{
		sk_filter_release(fp);
		__sk_filter_release(fp);
		}
		EXPORT_SYMBOL_GPL(sk_unattached_filter_destroy);

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