From 8d26d1a24bd8523902d8987a9b69462380c70fc3 Mon Sep 17 00:00:00 2001 From: Jukka Taimisto Date: Thu, 22 May 2014 10:02:39 +0000 Subject: [PATCH] Bluetooth: Fix L2CAP deadlock MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit commit 8a96f3cd22878fc0bb564a8478a6e17c0b8dca73 upstream. -[0x01 Introduction We have found a programming error causing a deadlock in Bluetooth subsystem of Linux kernel. The problem is caused by missing release_sock() call when L2CAP connection creation fails due full accept queue. The issue can be reproduced with 3.15-rc5 kernel and is also present in earlier kernels. -[0x02 Details The problem occurs when multiple L2CAP connections are created to a PSM which contains listening socket (like SDP) and left pending, for example, configuration (the underlying ACL link is not disconnected between connections). When L2CAP connection request is received and listening socket is found the l2cap_sock_new_connection_cb() function (net/bluetooth/l2cap_sock.c) is called. This function locks the 'parent' socket and then checks if the accept queue is full. 1178 lock_sock(parent); 1179 1180 /* Check for backlog size */ 1181 if (sk_acceptq_is_full(parent)) { 1182 BT_DBG("backlog full %d", parent->sk_ack_backlog); 1183 return NULL; 1184 } If case the accept queue is full NULL is returned, but the 'parent' socket is not released. Thus when next L2CAP connection request is received the code blocks on lock_sock() since the parent is still locked. Also note that for connections already established and waiting for configuration to complete a timeout will occur and l2cap_chan_timeout() (net/bluetooth/l2cap_core.c) will be called. All threads calling this function will also be blocked waiting for the channel mutex since the thread which is waiting on lock_sock() alread holds the channel mutex. We were able to reproduce this by sending continuously L2CAP connection request followed by disconnection request containing invalid CID. This left the created connections pending configuration. After the deadlock occurs it is impossible to kill bluetoothd, btmon will not get any more data etc. requiring reboot to recover. -[0x03 Fix Releasing the 'parent' socket when l2cap_sock_new_connection_cb() returns NULL seems to fix the issue. Signed-off-by: Jukka Taimisto Reported-by: Tommi Mäkilä Signed-off-by: Johan Hedberg Signed-off-by: Greg Kroah-Hartman --- net/bluetooth/l2cap_sock.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/net/bluetooth/l2cap_sock.c b/net/bluetooth/l2cap_sock.c index 36fed40c162c..302d29b3744d 100644 --- a/net/bluetooth/l2cap_sock.c +++ b/net/bluetooth/l2cap_sock.c @@ -949,13 +949,16 @@ static struct l2cap_chan *l2cap_sock_new_connection_cb(struct l2cap_chan *chan) /* Check for backlog size */ if (sk_acceptq_is_full(parent)) { BT_DBG("backlog full %d", parent->sk_ack_backlog); + release_sock(parent); return NULL; } sk = l2cap_sock_alloc(sock_net(parent), NULL, BTPROTO_L2CAP, GFP_ATOMIC); - if (!sk) + if (!sk) { + release_sock(parent); return NULL; + } bt_sock_reclassify_lock(sk, BTPROTO_L2CAP); -- 2.20.1