[PATCH 5.11 06/31] mptcp: dispose initial struct socket when its subflow is closed

[Greg Kroah-Hartman]

From: Florian Westphal <f...@strlen.de>

[ Upstream commit 17aee05dc8822e354f5ad2d68ee39e3ba4b6acf2 ]

Christoph Paasch reported following crash:
dst_release underflow
WARNING: CPU: 0 PID: 1319 at net/core/dst.c:175 dst_release+0xc1/0xd0 
net/core/dst.c:175
CPU: 0 PID: 1319 Comm: syz-executor217 Not tainted 
5.11.0-rc6af8e85128b4d0d24083c5cac646e891227052e0c #70
Call Trace:
 rt_cache_route+0x12e/0x140 net/ipv4/route.c:1503
 rt_set_nexthop.constprop.0+0x1fc/0x590 net/ipv4/route.c:1612
 __mkroute_output net/ipv4/route.c:2484 [inline]
...

The worker leaves msk->subflow alone even when it
happened to close the subflow ssk associated with it.

Fixes: 866f26f2a9c33b ("mptcp: always graft subflow socket to parent")
Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/157
Reported-by: Christoph Paasch <cpaa...@apple.com>
Suggested-by: Paolo Abeni <pab...@redhat.com>
Acked-by: Paolo Abeni <pab...@redhat.com>
Signed-off-by: Florian Westphal <f...@strlen.de>
Signed-off-by: Mat Martineau <mathew.j.martin...@linux.intel.com>
Signed-off-by: David S. Miller <da...@davemloft.net>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 net/mptcp/protocol.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 64b8a49652ae..7345df40385a 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2100,6 +2100,14 @@ static struct sock *mptcp_subflow_get_retrans(const 
struct mptcp_sock *msk)
        return backup;
 }
 
+static void mptcp_dispose_initial_subflow(struct mptcp_sock *msk)
+{
+       if (msk->subflow) {
+               iput(SOCK_INODE(msk->subflow));
+               msk->subflow = NULL;
+       }
+}
+
 /* subflow sockets can be either outgoing (connect) or incoming
  * (accept).
  *
@@ -2144,6 +2152,9 @@ void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 
        if (ssk == msk->last_snd)
                msk->last_snd = NULL;
+
+       if (msk->subflow && ssk == msk->subflow->sk)
+               mptcp_dispose_initial_subflow(msk);
 }
 
 static unsigned int mptcp_sync_mss(struct sock *sk, u32 pmtu)
@@ -2533,12 +2544,6 @@ static void __mptcp_destroy_sock(struct sock *sk)
 
        might_sleep();
 
-       /* dispose the ancillatory tcp socket, if any */
-       if (msk->subflow) {
-               iput(SOCK_INODE(msk->subflow));
-               msk->subflow = NULL;
-       }
-
        /* be sure to always acquire the join list lock, to sync vs
         * mptcp_finish_join().
         */
@@ -2563,6 +2568,7 @@ static void __mptcp_destroy_sock(struct sock *sk)
        sk_stream_kill_queues(sk);
        xfrm_sk_free_policy(sk);
        sk_refcnt_debug_release(sk);
+       mptcp_dispose_initial_subflow(msk);
        sock_put(sk);
 }
 
-- 
2.30.1