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mptcp: be careful on MPTCP-level ack.

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We can enter the main mptcp_recvmsg() loop even when
no subflows are connected. As note by Eric, that would
result in a divide by zero oops on ack generation.

Address the issue by checking the subflow status before
sending the ack.

Additionally protect mptcp_recvmsg() against invocation
with weird socket states.

v1 -> v2:
 - removed unneeded inline keyword - Jakub

Reported-and-suggested-by: Eric Dumazet <eric.dumazet@gmail.com>
Fixes: ea4ca586b1 ("mptcp: refine MPTCP-level ack scheduling")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Link: https://lore.kernel.org/r/5370c0ae03449239e3d1674ddcfb090cf6f20abe.1606253206.git.pabeni@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Paolo Abeni 2020-11-24 22:51:24 +01:00 committed by Jakub Kicinski
parent bfd042321a
commit fd8976790a
1 changed files with 49 additions and 18 deletions
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67
net/mptcp/protocol.c
View File

@ -419,31 +419,57 @@ static bool mptcp_subflow_active(struct mptcp_subflow_context *subflow)
return ((1 << ssk->sk_state) & (TCPF_ESTABLISHED | TCPF_CLOSE_WAIT));
}
static void mptcp_send_ack(struct mptcp_sock *msk, bool force)
static bool tcp_can_send_ack(const struct sock *ssk)
{
return !((1 << inet_sk_state_load(ssk)) &
(TCPF_SYN_SENT | TCPF_SYN_RECV | TCPF_TIME_WAIT | TCPF_CLOSE));
}
static void mptcp_send_ack(struct mptcp_sock *msk)
{
struct mptcp_subflow_context *subflow;
struct sock *pick = NULL;
mptcp_for_each_subflow(msk, subflow) {
struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
if (force) {
lock_sock(ssk);
lock_sock(ssk);
if (tcp_can_send_ack(ssk))
tcp_send_ack(ssk);
release_sock(ssk);
continue;
}
release_sock(ssk);
}
}
/* if the hintes ssk is still active, use it */
pick = ssk;
if (ssk == msk->ack_hint)
break;
}
if (!force && pick) {
lock_sock(pick);
tcp_cleanup_rbuf(pick, 1);
release_sock(pick);
static bool mptcp_subflow_cleanup_rbuf(struct sock *ssk)
{
int ret;
lock_sock(ssk);
ret = tcp_can_send_ack(ssk);
if (ret)
tcp_cleanup_rbuf(ssk, 1);
release_sock(ssk);
return ret;
}
static void mptcp_cleanup_rbuf(struct mptcp_sock *msk)
{
struct mptcp_subflow_context *subflow;
/* if the hinted ssk is still active, try to use it */
if (likely(msk->ack_hint)) {
mptcp_for_each_subflow(msk, subflow) {
struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
if (msk->ack_hint == ssk &&
mptcp_subflow_cleanup_rbuf(ssk))
return;
}
}
/* otherwise pick the first active subflow */
mptcp_for_each_subflow(msk, subflow)
if (mptcp_subflow_cleanup_rbuf(mptcp_subflow_tcp_sock(subflow)))
return;
}
static bool mptcp_check_data_fin(struct sock *sk)
@ -494,7 +520,7 @@ static bool mptcp_check_data_fin(struct sock *sk)
ret = true;
mptcp_set_timeout(sk, NULL);
mptcp_send_ack(msk, true);
mptcp_send_ack(msk);
mptcp_close_wake_up(sk);
}
return ret;
@ -1579,6 +1605,11 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
return -EOPNOTSUPP;
lock_sock(sk);
if (unlikely(sk->sk_state == TCP_LISTEN)) {
copied = -ENOTCONN;
goto out_err;
}
timeo = sock_rcvtimeo(sk, nonblock);
len = min_t(size_t, len, INT_MAX);
@ -1604,7 +1635,7 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
/* be sure to advertise window change */
old_space = READ_ONCE(msk->old_wspace);
if ((tcp_space(sk) - old_space) >= old_space)
mptcp_send_ack(msk, false);
mptcp_cleanup_rbuf(msk);
/* only the master socket status is relevant here. The exit
* conditions mirror closely tcp_recvmsg()