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Subject[068/152] filter: fix sk_filter rcu handling
2.6.36-stable review patch.  If anyone has any objections, please let us know.

------------------


From: Eric Dumazet <eric.dumazet@gmail.com>

[ Upstream commit 46bcf14f44d8f31ecfdc8b6708ec15a3b33316d9 ]

Pavel Emelyanov tried to fix a race between sk_filter_(de|at)tach and
sk_clone() in commit 47e958eac280c263397

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
include/net/sock.h | 4 +++-
net/core/filter.c | 19 ++++++-------------
2 files changed, 9 insertions(+), 14 deletions(-)

--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -1155,6 +1155,8 @@ extern void sk_common_release(struct soc
/* 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
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)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -589,23 +589,16 @@ int sk_chk_filter(struct sock_filter *fi
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
@@ -650,7 +643,7 @@ int sk_attach_filter(struct sock_fprog *
rcu_read_unlock_bh();

if (old_fp)
- sk_filter_delayed_uncharge(sk, old_fp);
+ sk_filter_uncharge(sk, old_fp);
return 0;
}
EXPORT_SYMBOL_GPL(sk_attach_filter);
@@ -664,7 +657,7 @@ int sk_detach_filter(struct sock *sk)
filter = rcu_dereference_bh(sk->sk_filter);
if (filter) {
rcu_assign_pointer(sk->sk_filter, NULL);
- sk_filter_delayed_uncharge(sk, filter);
+ sk_filter_uncharge(sk, filter);
ret = 0;
}
rcu_read_unlock_bh();



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