netdev - [PATCH net] net, sk_msg: Don't check if sock is locked when tearing down psock

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Message-Id: <20200121123147.706666-1-jakub@cloudflare.com>
Date:   Tue, 21 Jan 2020 13:31:47 +0100
From:   Jakub Sitnicki <jakub@...udflare.com>
To:     netdev@...r.kernel.org
Cc:     John Fastabend <john.fastabend@...il.com>,
        syzbot+d73682fcf7fee6982fe3@...kaller.appspotmail.com
Subject: [PATCH net] net, sk_msg: Don't check if sock is locked when tearing down psock

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

diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index 3866d7e20c07..ded2d5227678 100644
--- 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);
 
-- 
2.24.1