mptcp: fix sk_forward_memory corruption on retransmission

MPTCP sk_forward_memory handling is a bit special, as such field
is protected by the msk socket spin_lock, instead of the plain
socket lock.

Currently we have a code path updating such field without handling
the relevant lock:

__mptcp_retrans() -> __mptcp_clean_una_wakeup()

Several helpers in __mptcp_clean_una_wakeup() will update
sk_forward_alloc, possibly causing such field corruption, as reported
by Matthieu.

Address the issue providing and using a new variant of blamed function
which explicitly acquires the msk spin lock.

Fixes: 64b9cea7a0af ("mptcp: fix spurious retransmissions")
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/172
Reported-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Tested-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 2bc1995..5edc686 100644 (file)
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -947,6 +947,10 @@ static void __mptcp_update_wmem(struct sock *sk)
 {
        struct mptcp_sock *msk = mptcp_sk(sk);
 
+#ifdef CONFIG_LOCKDEP
+       WARN_ON_ONCE(!lockdep_is_held(&sk->sk_lock.slock));
+#endif
+
        if (!msk->wmem_reserved)
                return;
 
@@ -1085,10 +1089,20 @@ out:
 
 static void __mptcp_clean_una_wakeup(struct sock *sk)
 {
+#ifdef CONFIG_LOCKDEP
+       WARN_ON_ONCE(!lockdep_is_held(&sk->sk_lock.slock));
+#endif
        __mptcp_clean_una(sk);
        mptcp_write_space(sk);
 }
 
+static void mptcp_clean_una_wakeup(struct sock *sk)
+{
+       mptcp_data_lock(sk);
+       __mptcp_clean_una_wakeup(sk);
+       mptcp_data_unlock(sk);
+}
+
 static void mptcp_enter_memory_pressure(struct sock *sk)
 {
        struct mptcp_subflow_context *subflow;
@@ -2299,7 +2313,7 @@ static void __mptcp_retrans(struct sock *sk)
        struct sock *ssk;
        int ret;
 
-       __mptcp_clean_una_wakeup(sk);
+       mptcp_clean_una_wakeup(sk);
        dfrag = mptcp_rtx_head(sk);
        if (!dfrag) {
                if (mptcp_data_fin_enabled(msk)) {