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authorSabrina Dubroca <sd@queasysnail.net>2017-08-25 13:10:12 +0200
committerDavid S. Miller <davem@davemloft.net>2017-08-25 17:16:27 -0700
commitebfa00c5745660fe7f0a91eea88d4dff658486c4 (patch)
tree70f899bdadb25a073dc98f97bac41e60a149077a /net
parent3614364527daa870264f6dde77f02853cdecd02c (diff)
tcp: fix refcnt leak with ebpf congestion control
There are a few bugs around refcnt handling in the new BPF congestion control setsockopt: - The new ca is assigned to icsk->icsk_ca_ops even in the case where we cannot get a reference on it. This would lead to a use after free, since that ca is going away soon. - Changing the congestion control case doesn't release the refcnt on the previous ca. - In the reinit case, we first leak a reference on the old ca, then we call tcp_reinit_congestion_control on the ca that we have just assigned, leading to deinitializing the wrong ca (->release of the new ca on the old ca's data) and releasing the refcount on the ca that we actually want to use. This is visible by building (for example) BIC as a module and setting net.ipv4.tcp_congestion_control=bic, and using tcp_cong_kern.c from samples/bpf. This patch fixes the refcount issues, and moves reinit back into tcp core to avoid passing a ca pointer back to BPF. Fixes: 91b5b21c7c16 ("bpf: Add support for changing congestion control") Signed-off-by: Sabrina Dubroca <sd@queasysnail.net> Acked-by: Lawrence Brakmo <brakmo@fb.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/core/filter.c7
-rw-r--r--net/ipv4/tcp.c2
-rw-r--r--net/ipv4/tcp_cong.c19
3 files changed, 17 insertions, 11 deletions
diff --git a/net/core/filter.c b/net/core/filter.c
index 8eb81e5fae08..169974998c76 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2836,15 +2836,12 @@ BPF_CALL_5(bpf_setsockopt, struct bpf_sock_ops_kern *, bpf_sock,
sk->sk_prot->setsockopt == tcp_setsockopt) {
if (optname == TCP_CONGESTION) {
char name[TCP_CA_NAME_MAX];
+ bool reinit = bpf_sock->op > BPF_SOCK_OPS_NEEDS_ECN;
strncpy(name, optval, min_t(long, optlen,
TCP_CA_NAME_MAX-1));
name[TCP_CA_NAME_MAX-1] = 0;
- ret = tcp_set_congestion_control(sk, name, false);
- if (!ret && bpf_sock->op > BPF_SOCK_OPS_NEEDS_ECN)
- /* replacing an existing ca */
- tcp_reinit_congestion_control(sk,
- inet_csk(sk)->icsk_ca_ops);
+ ret = tcp_set_congestion_control(sk, name, false, reinit);
} else {
struct tcp_sock *tp = tcp_sk(sk);
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 71ce33decd97..a3e91b552edc 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2481,7 +2481,7 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
name[val] = 0;
lock_sock(sk);
- err = tcp_set_congestion_control(sk, name, true);
+ err = tcp_set_congestion_control(sk, name, true, true);
release_sock(sk);
return err;
}
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index fde983f6376b..421ea1b918da 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -189,8 +189,8 @@ void tcp_init_congestion_control(struct sock *sk)
INET_ECN_dontxmit(sk);
}
-void tcp_reinit_congestion_control(struct sock *sk,
- const struct tcp_congestion_ops *ca)
+static void tcp_reinit_congestion_control(struct sock *sk,
+ const struct tcp_congestion_ops *ca)
{
struct inet_connection_sock *icsk = inet_csk(sk);
@@ -338,7 +338,7 @@ out:
* tcp_reinit_congestion_control (if the current congestion control was
* already initialized.
*/
-int tcp_set_congestion_control(struct sock *sk, const char *name, bool load)
+int tcp_set_congestion_control(struct sock *sk, const char *name, bool load, bool reinit)
{
struct inet_connection_sock *icsk = inet_csk(sk);
const struct tcp_congestion_ops *ca;
@@ -360,9 +360,18 @@ int tcp_set_congestion_control(struct sock *sk, const char *name, bool load)
if (!ca) {
err = -ENOENT;
} else if (!load) {
- icsk->icsk_ca_ops = ca;
- if (!try_module_get(ca->owner))
+ const struct tcp_congestion_ops *old_ca = icsk->icsk_ca_ops;
+
+ if (try_module_get(ca->owner)) {
+ if (reinit) {
+ tcp_reinit_congestion_control(sk, ca);
+ } else {
+ icsk->icsk_ca_ops = ca;
+ module_put(old_ca->owner);
+ }
+ } else {
err = -EBUSY;
+ }
} else if (!((ca->flags & TCP_CONG_NON_RESTRICTED) ||
ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN))) {
err = -EPERM;