Hi Gustavo,
Thanks for reviewing the patch. Please check new patches attached and
comments below:
On Sun, May 16, 2010 at 11:31 AM, Gustavo F. Padovan
<gustavo@xxxxxxxxxxx> wrote:
> Hi Andrei,
>
> * Andrei Emeltchenko <andrei.emeltchenko.news@xxxxxxxxx> [2010-05-14 18:39:40 +0300]:
>
>> Hi all,
>>
>> We have a bug with race condition between l2cap tasklet and krfcomm process.
>>
>> When sending following sequence:
>>
>> ...
>> No. Time Source Destination Protocol Info
>> 89 1.951202 RFCOMM Rcvd DISC DLCI=20
>> 90 1.951324 RFCOMM Sent UA DLCI=20
>> 91 1.959381 HCI_EVT Number of Completed Packets
>> 92 1.966461 RFCOMM Rcvd DISC DLCI=0
>> 93 1.966492 L2CAP Rcvd Disconnect Request
>> 94 1.972595 L2CAP Sent Disconnect Response
>>
>> ...
>>
>> krfcommd kernel thread is preempted with l2cap tasklet which remove l2cap_conn
>> (L2CAP connection handler structure). Then rfcomm thread tries to send RFCOMM
>> UA which is reply to RFCOMM DISC and when de-referencing l2cap_conn crash
>> happens.
>>
>> ...
>> [ 694.175933] Unable to handle kernel NULL pointer dereference at
>> virtual address 00000000
>> [ 694.184936] pgd = c0004000
>> [ 694.187683] [00000000] *pgd=00000000
>> [ 694.191711] Internal error: Oops: 5 [#1] PREEMPT
>> [ 694.196350] last sysfs file:
>> /sys/devices/platform/hci_h4p/firmware/hci_h4p/loading
>> [ 694.260375] CPU: 0 Not tainted (2.6.32.10 #1)
>> [ 694.265106] PC is at l2cap_sock_sendmsg+0x43c/0x73c [l2cap]
>> [ 694.270721] LR is at 0xd7017303
>> ...
>> [ 694.525085] Backtrace:
>> [ 694.527587] [<bf266be0>] (l2cap_sock_sendmsg+0x0/0x73c [l2cap])
>> from [<c02f2cc8>] (sock_sendmsg+0xb8
>> [ 694.537292] [<c02f2c10>] (sock_sendmsg+0x0/0xd8) from [<c02f3044>]
>> (kernel_sendmsg+0x48/0x80)
>> ...
>>
>> I have a patch which fixes the issue but not sure that there is no
>> better way. Waiting for comments.
>>
>> Currently I am investigating possibility to:
>> - implement l2cap_conn reference counting
>
> sock_owned_by_user() gives the same effect as a ref count. See comments below.
>
Yes. For this cases this is enough. But proper refcounting is always
better than this "effects" ;)
>> - use socket backlog queue to process l2cap packets later when socket is not
>> owned by the process.
>
> You actually don't need a backlog queue here. You can process the signal
> packet, skipping the l2cap_chan_del() call;
>
...
>> + /* sk is locked in krfcomm process */
>> + if (sock_owned_by_user(sk)) {
>> + BT_DBG("sk %p is owned by user", sk);
>> + bh_unlock_sock(sk);
>> + return 0;
>> + }
>
> That's wrong. Use the sock_owned_by_user() only to avoid the
> l2cap_chan_del() call, so you can process all the rest of the function
> and send the Disconnect Response.
I have changed the patch so that it only prevents l2cap_chan_del
- l2cap_chan_del(sk, ECONNREFUSED);
+ /* delete l2cap channel if sk is not owned by user */
+ if (!sock_owned_by_user(sk))
+ l2cap_chan_del(sk, ECONNREFUSED);
Then still l2cap_sock_kill(sk) removes sk but in the second patch sk is
hold with sock_hold(sk) until rfcomm is still processing packet.
> The same check should be added to l2cap_connect_rsp() and
> l2cap_disconnect_rsp(), since they call l2cap_chan_del() under bh
> context as well. ;)
Added.
Regards,
Andrei Emeltchenko
From 8531c8add8a378fc24b92f2c2311b01a7b1f63fc Mon Sep 17 00:00:00 2001
From: Andrei Emeltchenko <andrei.emeltchenko@xxxxxxxxx>
Date: Mon, 17 May 2010 12:10:46 +0300
Subject: [PATCH 1/2] Bluetooth: Check sk is not owned before freeing l2cap_conn
Check that socket sk is not locked in user process before removing
l2cap connection handler.
krfcommd kernel thread may be preempted with l2cap tasklet which remove
l2cap_conn structure. If krfcommd is in process of sending of RFCOMM reply
(like "RFCOMM UA" reply to "RFCOMM DISC") then kernel crash happens.
...
[ 694.175933] Unable to handle kernel NULL pointer dereference at virtual address 00000000
[ 694.184936] pgd = c0004000
[ 694.187683] [00000000] *pgd=00000000
[ 694.191711] Internal error: Oops: 5 [#1] PREEMPT
[ 694.196350] last sysfs file: /sys/devices/platform/hci_h4p/firmware/hci_h4p/loading
[ 694.260375] CPU: 0 Not tainted (2.6.32.10 #1)
[ 694.265106] PC is at l2cap_sock_sendmsg+0x43c/0x73c [l2cap]
[ 694.270721] LR is at 0xd7017303
...
[ 694.525085] Backtrace:
[ 694.527587] [<bf266be0>] (l2cap_sock_sendmsg+0x0/0x73c [l2cap]) from [<c02f2cc8>] (sock_sendmsg+0xb8/0xd8)
[ 694.537292] [<c02f2c10>] (sock_sendmsg+0x0/0xd8) from [<c02f3044>] (kernel_sendmsg+0x48/0x80)
...
Modified version after comments of Gustavo F. Padovan <gustavo@xxxxxxxxxxx>
Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@xxxxxxxxx>
---
net/bluetooth/l2cap.c | 14 +++++++++++---
1 files changed, 11 insertions(+), 3 deletions(-)
diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index bb00015..794f2b7 100644
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -2927,7 +2927,9 @@ static inline int l2cap_connect_rsp(struct l2cap_conn *conn, struct l2cap_cmd_hd
break;
default:
- l2cap_chan_del(sk, ECONNREFUSED);
+ /* delete l2cap channel if sk is not owned by user */
+ if (!sock_owned_by_user(sk))
+ l2cap_chan_del(sk, ECONNREFUSED);
break;
}
@@ -3135,7 +3137,10 @@ static inline int l2cap_disconnect_req(struct l2cap_conn *conn, struct l2cap_cmd
del_timer(&l2cap_pi(sk)->ack_timer);
}
- l2cap_chan_del(sk, ECONNRESET);
+ /* delete l2cap channel if sk is not owned by user */
+ if (!sock_owned_by_user(sk))
+ l2cap_chan_del(sk, ECONNRESET);
+
bh_unlock_sock(sk);
l2cap_sock_kill(sk);
@@ -3167,7 +3172,10 @@ static inline int l2cap_disconnect_rsp(struct l2cap_conn *conn, struct l2cap_cmd
del_timer(&l2cap_pi(sk)->ack_timer);
}
- l2cap_chan_del(sk, 0);
+ /* delete l2cap channel if sk is not owned by user */
+ if (!sock_owned_by_user(sk))
+ l2cap_chan_del(sk, 0);
+
bh_unlock_sock(sk);
l2cap_sock_kill(sk);
--
1.7.0.4
From 99ffb4e41ff46022cbc52f3c947425791de7fa39 Mon Sep 17 00:00:00 2001
From: Andrei Emeltchenko <andrei.emeltchenko@xxxxxxxxx>
Date: Mon, 17 May 2010 12:28:06 +0300
Subject: [PATCH 2/2] Bluetooth: Prevent sk freeing in tasklet using refcount
Socket sk may be freed in tasklet while still be in use in krfcommd
process. Use refcount to mark sk as used.
Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@xxxxxxxxx>
---
net/bluetooth/l2cap.c | 2 ++
1 files changed, 2 insertions(+), 0 deletions(-)
diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index 794f2b7..bf762d6 100644
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -1724,6 +1724,7 @@ static int l2cap_sock_sendmsg(struct kiocb *iocb, struct socket *sock, struct ms
if (msg->msg_flags & MSG_OOB)
return -EOPNOTSUPP;
+ sock_hold(sk);
lock_sock(sk);
if (sk->sk_state != BT_CONNECTED) {
@@ -1808,6 +1809,7 @@ static int l2cap_sock_sendmsg(struct kiocb *iocb, struct socket *sock, struct ms
done:
release_sock(sk);
+ sock_put(sk);
return err;
}
--
1.7.0.4
