Patch "mptcp: dispose initial struct socket when its subflow is closed" has been added to the 5.11-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    mptcp: dispose initial struct socket when its subflow is closed

to the 5.11-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mptcp-dispose-initial-struct-socket-when-its-subflow.patch
and it can be found in the queue-5.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit c89c754d4d6b941c7c6bf4621cdac12ce68b3bcc
Author: Florian Westphal <fw@xxxxxxxxx>
Date:   Thu Mar 4 13:32:11 2021 -0800

    mptcp: dispose initial struct socket when its subflow is closed
    
    [ 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 <cpaasch@xxxxxxxxx>
    Suggested-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Acked-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Signed-off-by: Florian Westphal <fw@xxxxxxxxx>
    Signed-off-by: Mat Martineau <mathew.j.martineau@xxxxxxxxxxxxxxx>
    Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

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);
 }