socket, bpf: fix possible use after free
Starting from linux-4.4, 3WHS no longer takes the listener lock.
Since this time, we might hit a use-after-free in sk_filter_charge(),
if the filter we got in the memcpy() of the listener content
just happened to be replaced by a thread changing listener BPF filter.
To fix this, we need to make sure the filter refcount is not already
zero before incrementing it again.
Fixes: e994b2f0fb92 ("tcp: do not lock listener to process SYN packets")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/filter.c b/net/core/filter.c
index 82edad5..74b8c91 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -989,10 +989,14 @@
bool sk_filter_charge(struct sock *sk, struct sk_filter *fp)
{
- bool ret = __sk_filter_charge(sk, fp);
- if (ret)
- refcount_inc(&fp->refcnt);
- return ret;
+ if (!refcount_inc_not_zero(&fp->refcnt))
+ return false;
+
+ if (!__sk_filter_charge(sk, fp)) {
+ sk_filter_release(fp);
+ return false;
+ }
+ return true;
}
static struct bpf_prog *bpf_migrate_filter(struct bpf_prog *fp)
diff --git a/net/core/sock.c b/net/core/sock.c
index 7d55c05..23953b7 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1684,13 +1684,16 @@
sock_reset_flag(newsk, SOCK_DONE);
- filter = rcu_dereference_protected(newsk->sk_filter, 1);
+ rcu_read_lock();
+ filter = rcu_dereference(sk->sk_filter);
if (filter != NULL)
/* though it's an empty new sock, the charging may fail
* if sysctl_optmem_max was changed between creation of
* original socket and cloning
*/
is_charged = sk_filter_charge(newsk, filter);
+ RCU_INIT_POINTER(newsk->sk_filter, filter);
+ rcu_read_unlock();
if (unlikely(!is_charged || xfrm_sk_clone_policy(newsk, sk))) {
/* We need to make sure that we don't uncharge the new
