linux-kernel - [PATCH] Bluetooth: Fix locking in bt_accept

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Message-Id: <20181015223910.197729-1-mka@chromium.org>
Date:   Mon, 15 Oct 2018 15:39:10 -0700
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Marcel Holtmann <marcel@...tmann.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Dean Jenkins <Dean_Jenkins@...tor.com>
Cc:     linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Konstantin Khlebnikov <khlebnikov@...dex-team.ru>,
        Balakrishna Godavarthi <bgodavar@...eaurora.org>,
        Douglas Anderson <dianders@...omium.org>,
        Dmitry Grinberg <dmitrygr@...gle.com>,
        Matthias Kaehlcke <mka@...omium.org>
Subject: [PATCH] Bluetooth: Fix locking in bt_accept_enqueue() for BH context

With commit e16337622016 ("Bluetooth: Handle bt_accept_enqueue() socket
atomically") lock_sock[_nested]() is used to acquire the socket lock
before manipulating the socket. lock_sock[_nested]() may block, which
is problematic since bt_accept_enqueue() can be called in bottom half
context (e.g. from rfcomm_connect_ind()).

The socket API provides bh_lock_sock[_nested]() to acquire the socket
lock in bottom half context. Check the context in bt_accept_enqueue()
and use the appropriate locking mechanism for the context.

Fixes: e16337622016 ("Bluetooth: Handle bt_accept_enqueue() socket atomically")
Signed-off-by: Matthias Kaehlcke <mka@...omium.org>
---
Not sure if this is the correct solution, it's certainly not elegant and
checkpatch.pl complains that in_atomic() shouldn't be used outside of
core kernel code. I'm open to other suggestions :)

 net/bluetooth/af_bluetooth.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/af_bluetooth.c b/net/bluetooth/af_bluetooth.c
index deacc52d7ff1..0f0540dbb44a 100644
--- a/net/bluetooth/af_bluetooth.c
+++ b/net/bluetooth/af_bluetooth.c
@@ -159,10 +159,20 @@ void bt_accept_enqueue(struct sock *parent, struct sock *sk)
 	BT_DBG("parent %p, sk %p", parent, sk);
 
 	sock_hold(sk);
-	lock_sock_nested(sk, SINGLE_DEPTH_NESTING);
+
+	if (in_atomic())
+		bh_lock_sock_nested(sk);
+	else
+		lock_sock_nested(sk, SINGLE_DEPTH_NESTING);
+
 	list_add_tail(&bt_sk(sk)->accept_q, &bt_sk(parent)->accept_q);
 	bt_sk(sk)->parent = parent;
-	release_sock(sk);
+
+	if (in_atomic())
+		bh_unlock_sock(sk);
+	else
+		release_sock(sk);
+
 	parent->sk_ack_backlog++;
 }
 EXPORT_SYMBOL(bt_accept_enqueue);
-- 
2.19.1.331.ge82ca0e54c-goog