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Commit 8873c064 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp: do not release socket ownership in tcp_close() 



syzkaller was able to hit the WARN_ON(sock_owned_by_user(sk));
in tcp_close()

While a socket is being closed, it is very possible other
threads find it in rtnetlink dump.

tcp_get_info() will acquire the socket lock for a short amount
of time (slow = lock_sock_fast(sk)/unlock_sock_fast(sk, slow);),
enough to trigger the warning.

Fixes: 67db3e4b ("tcp: no longer hold ehash lock while calling tcp_get_info()")
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Reported-by: default avatarsyzbot <syzkaller@googlegroups.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 744486d4

include/net/sock.h

+1 −0
Original line number Diff line number Diff line
@@ -1492,6 +1492,7 @@ static inline void lock_sock(struct sock *sk) 
	lock_sock_nested(sk, 0);

}



void __release_sock(struct sock *sk);

void release_sock(struct sock *sk);



/* BH context may only use the following locking interface. */

net/core/sock.c

+1 −1
Original line number Diff line number Diff line
@@ -2317,7 +2317,7 @@ static void __lock_sock(struct sock *sk) 
	finish_wait(&sk->sk_lock.wq, &wait);

}



static void __release_sock(struct sock *sk)

void __release_sock(struct sock *sk)

	__releases(&sk->sk_lock.slock)

	__acquires(&sk->sk_lock.slock)

{

net/ipv4/tcp.c

+3 −8
Original line number Diff line number Diff line
@@ -2416,16 +2416,10 @@ void tcp_close(struct sock *sk, long timeout) 
	sock_hold(sk);

	sock_orphan(sk);



	/* It is the last release_sock in its life. It will remove backlog. */

	release_sock(sk);





	/* Now socket is owned by kernel and we acquire BH lock

	 *  to finish close. No need to check for user refs.

	 */

	local_bh_disable();

	bh_lock_sock(sk);

	WARN_ON(sock_owned_by_user(sk));

	/* remove backlog if any, without releasing ownership. */

	__release_sock(sk);



	percpu_counter_inc(sk->sk_prot->orphan_count);
@@ -2494,6 +2488,7 @@ void tcp_close(struct sock *sk, long timeout) 
out:

	bh_unlock_sock(sk);

	local_bh_enable();

	release_sock(sk);

	sock_put(sk);

}

EXPORT_SYMBOL(tcp_close);