Commit 46bcf14f authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

filter: fix sk_filter rcu handling

Pavel Emelyanov tried to fix a race between sk_filter_(de|at)tach and
sk_clone() in commit 47e958ea

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: default avatarEric Dumazet <>
Signed-off-by: default avatarDavid S. Miller <>
parent e7dfc8db
......@@ -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))
call_rcu_bh(&fp->rcu, sk_filter_release_rcu);
static inline void sk_filter_uncharge(struct sock *sk, struct sk_filter *fp)
......@@ -589,23 +589,16 @@ int sk_chk_filter(struct sock_filter *filter, int flen)
* 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);
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);
* 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;
......@@ -663,7 +656,7 @@ int sk_detach_filter(struct sock *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;
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