linux-kernel - [PATCH 5.4 084/104] net, sk_msg: Dont check if sock is locked when tearing down psock

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Date:   Tue, 28 Jan 2020 15:00:45 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+d73682fcf7fee6982fe3@...kaller.appspotmail.com,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 5.4 084/104] net, sk_msg: Dont check if sock is locked when tearing down psock

From: Jakub Sitnicki <jakub@...udflare.com>

commit 58c8db929db1c1d785a6f5d8f8692e5dbcc35e84 upstream.

As John Fastabend reports [0], psock state tear-down can happen on receive
path *after* unlocking the socket, if the only other psock user, that is
sockmap or sockhash, releases its psock reference before tcp_bpf_recvmsg
does so:

 tcp_bpf_recvmsg()
  psock = sk_psock_get(sk)                         <- refcnt 2
  lock_sock(sk);
  ...
                                  sock_map_free()  <- refcnt 1
  release_sock(sk)
  sk_psock_put()                                   <- refcnt 0

Remove the lockdep check for socket lock in psock tear-down that got
introduced in 7e81a3530206 ("bpf: Sockmap, ensure sock lock held during
tear down").

[0] https://lore.kernel.org/netdev/5e25dc995d7d_74082aaee6e465b441@john-XPS-13-9370.notmuch/

Fixes: 7e81a3530206 ("bpf: Sockmap, ensure sock lock held during tear down")
Reported-by: syzbot+d73682fcf7fee6982fe3@...kaller.appspotmail.com
Suggested-by: John Fastabend <john.fastabend@...il.com>
Signed-off-by: Jakub Sitnicki <jakub@...udflare.com>
Acked-by: John Fastabend <john.fastabend@...il.com>
Acked-by: Daniel Borkmann <daniel@...earbox.net>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 net/core/skmsg.c |    2 --
 1 file changed, 2 deletions(-)

--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -594,8 +594,6 @@ EXPORT_SYMBOL_GPL(sk_psock_destroy);
 
 void sk_psock_drop(struct sock *sk, struct sk_psock *psock)
 {
-	sock_owned_by_me(sk);
-
 	sk_psock_cork_free(psock);
 	sk_psock_zap_ingress(psock);