From: Eric Dumazet Date: Mon, 2 Oct 2017 19:20:51 +0000 (-0700) Subject: socket, bpf: fix possible use after free X-Git-Tag: v4.13.6~114 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=83c46af1d5e92d188649891f86d6c12219f45f91;p=thirdparty%2Fkernel%2Fstable.git socket, bpf: fix possible use after free [ Upstream commit eefca20eb20c66b06cf5ed09b49b1a7caaa27b7b ] 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 Acked-by: Alexei Starovoitov Acked-by: Daniel Borkmann Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- diff --git a/net/core/filter.c b/net/core/filter.c index 169974998c769..18d591f1ae5ae 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -975,10 +975,14 @@ 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) diff --git a/net/core/sock.c b/net/core/sock.c index b22228901a11f..0967da9250228 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -1675,13 +1675,16 @@ 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