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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: e994b2f0fb ("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>
This commit is contained in:
Eric Dumazet 2017-10-02 12:20:51 -07:00 committed by David S. Miller
parent 4ee4553e86
commit eefca20eb2
2 changed files with 12 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
net/core/filter.c
View File

@ -989,10 +989,14 @@ static bool __sk_filter_charge(struct sock *sk, struct sk_filter *fp)
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)

5
net/core/sock.c
View File

@ -1684,13 +1684,16 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
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