[PATCHv3 0/2] Fix kernel crash in rfcomm/l2cap

[PATCHv3 0/2] Fix kernel crash in rfcomm/l2cap

[Emeltchenko Andrei]

From: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>

Yet another version of patches fixing kernel crash in RFCOMM / L2CAP.

Do not delete l2cap channel and socket sk when sk is owned by user.
To delete l2cap channel standard timer is used.

lock_sock and release_sock do not hold a normal spinlock directly but 
instead hold the owner field. This means bh_lock_sock can still execute
even if the socket is "locked". More info can be found here:
http://www.linuxfoundation.org/collaborate/workgroups/networking/socketlocks

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.

Andrei Emeltchenko (2):
  Bluetooth: Check sk is not owned before freeing l2cap_conn
  Bluetooth: timer check sk is not owned before freeing

 net/bluetooth/l2cap.c |   58 ++++++++++++++++++++++++++++++++++++++----------
 1 files changed, 46 insertions(+), 12 deletions(-)

[PATCHv3 1/2] Bluetooth: Check sk is not owned before freeing l2cap_conn

[Emeltchenko Andrei]

From: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>

Check that socket sk is not locked in user process before removing
l2cap connection handler.

lock_sock and release_sock do not hold a normal spinlock directly but
instead hold the owner field. This means bh_lock_sock can still execute
even if the socket is "locked". More info can be found here:
http://www.linuxfoundation.org/collaborate/workgroups/networking/socketlocks

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)

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
---
 net/bluetooth/l2cap.c |   26 ++++++++++++++++++++++++++
 1 files changed, 26 insertions(+), 0 deletions(-)

diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index 6f931cc..b1344d8 100644
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -3078,6 +3078,14 @@ static inline int l2cap_connect_rsp(struct l2cap_conn *conn, struct l2cap_cmd_hd
 		break;
 
 	default:
+		/* don't delete l2cap channel if sk is owned by user */
+		if (sock_owned_by_user(sk)) {
+			sk->sk_state = BT_DISCONN;
+			l2cap_sock_clear_timer(sk);
+			l2cap_sock_set_timer(sk, HZ);
+			break;
+		}
+
 		l2cap_chan_del(sk, ECONNREFUSED);
 		break;
 	}
@@ -3283,6 +3291,15 @@ static inline int l2cap_disconnect_req(struct l2cap_conn *conn, struct l2cap_cmd
 
 	sk->sk_shutdown = SHUTDOWN_MASK;
 
+	/* don't delete l2cap channel if sk is owned by user */
+	if (sock_owned_by_user(sk)) {
+		sk->sk_state = BT_DISCONN;
+		l2cap_sock_clear_timer(sk);
+		l2cap_sock_set_timer(sk, HZ);
+		bh_unlock_sock(sk);
+		return 0;
+	}
+
 	l2cap_chan_del(sk, ECONNRESET);
 	bh_unlock_sock(sk);
 
@@ -3305,6 +3322,15 @@ static inline int l2cap_disconnect_rsp(struct l2cap_conn *conn, struct l2cap_cmd
 	if (!sk)
 		return 0;
 
+	/* don't delete l2cap channel if sk is owned by user */
+	if (sock_owned_by_user(sk)) {
+		sk->sk_state = BT_DISCONN;
+		l2cap_sock_clear_timer(sk);
+		l2cap_sock_set_timer(sk, HZ);
+		bh_unlock_sock(sk);
+		return 0;
+	}
+
 	l2cap_chan_del(sk, 0);
 	bh_unlock_sock(sk);
 
-- 
1.7.0.4

Re: [PATCHv3 1/2] Bluetooth: Check sk is not owned before freeing l2cap_conn

[Gustavo F. Padovan]

Hi Andrei,

* Emeltchenko Andrei <Andrei.Emeltchenko.news@gmail.com> [2010-10-29 16:43:00 +0300]:

> From: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
> 
> Check that socket sk is not locked in user process before removing
> l2cap connection handler.
> 
> lock_sock and release_sock do not hold a normal spinlock directly but
> instead hold the owner field. This means bh_lock_sock can still execute
> even if the socket is "locked". More info can be found here:
> http://www.linuxfoundation.org/collaborate/workgroups/networking/socketlocks
> 
> 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)
> 
> Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
> ---
>  net/bluetooth/l2cap.c |   26 ++++++++++++++++++++++++++
>  1 files changed, 26 insertions(+), 0 deletions(-)
> 
> diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
> index 6f931cc..b1344d8 100644
> --- a/net/bluetooth/l2cap.c
> +++ b/net/bluetooth/l2cap.c
> @@ -3078,6 +3078,14 @@ static inline int l2cap_connect_rsp(struct l2cap_conn *conn, struct l2cap_cmd_hd
>  		break;
>  
>  	default:
> +		/* don't delete l2cap channel if sk is owned by user */
> +		if (sock_owned_by_user(sk)) {
> +			sk->sk_state = BT_DISCONN;
> +			l2cap_sock_clear_timer(sk);
> +			l2cap_sock_set_timer(sk, HZ);
> +			break;
> +		}
> +
>  		l2cap_chan_del(sk, ECONNREFUSED);
>  		break;
>  	}
> @@ -3283,6 +3291,15 @@ static inline int l2cap_disconnect_req(struct l2cap_conn *conn, struct l2cap_cmd
>  
>  	sk->sk_shutdown = SHUTDOWN_MASK;
>  
> +	/* don't delete l2cap channel if sk is owned by user */
> +	if (sock_owned_by_user(sk)) {
> +		sk->sk_state = BT_DISCONN;
> +		l2cap_sock_clear_timer(sk);
> +		l2cap_sock_set_timer(sk, HZ);
> +		bh_unlock_sock(sk);
> +		return 0;
> +	}
> +
>  	l2cap_chan_del(sk, ECONNRESET);
>  	bh_unlock_sock(sk);
>  
> @@ -3305,6 +3322,15 @@ static inline int l2cap_disconnect_rsp(struct l2cap_conn *conn, struct l2cap_cmd
>  	if (!sk)
>  		return 0;
>  
> +	/* don't delete l2cap channel if sk is owned by user */
> +	if (sock_owned_by_user(sk)) {
> +		sk->sk_state = BT_DISCONN;
> +		l2cap_sock_clear_timer(sk);
> +		l2cap_sock_set_timer(sk, HZ);

1 second is too much. Change it to HZ/5 as well. I think it is a
reasonable value. 

-- 
Gustavo F. Padovan
ProFUSION embedded systems - http://profusion.mobi

[PATCHv3 2/2] Bluetooth: timer check sk is not owned before freeing

[Emeltchenko Andrei]

From: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>

In timer context we might delete l2cap channel used by krfcommd.
The check makes sure that sk is not owned. If sk is owned we
restart timer for HZ/5.

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
---
 net/bluetooth/l2cap.c |   32 ++++++++++++++++++++------------
 1 files changed, 20 insertions(+), 12 deletions(-)

diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
index b1344d8..c67b3c6 100644
--- a/net/bluetooth/l2cap.c
+++ b/net/bluetooth/l2cap.c
@@ -83,6 +83,18 @@ static struct sk_buff *l2cap_build_cmd(struct l2cap_conn *conn,
 static int l2cap_ertm_data_rcv(struct sock *sk, struct sk_buff *skb);
 
 /* ---- L2CAP timers ---- */
+static void l2cap_sock_set_timer(struct sock *sk, long timeout)
+{
+	BT_DBG("sk %p state %d timeout %ld", sk, sk->sk_state, timeout);
+	sk_reset_timer(sk, &sk->sk_timer, jiffies + timeout);
+}
+
+static void l2cap_sock_clear_timer(struct sock *sk)
+{
+	BT_DBG("sock %p state %d", sk, sk->sk_state);
+	sk_stop_timer(sk, &sk->sk_timer);
+}
+
 static void l2cap_sock_timeout(unsigned long arg)
 {
 	struct sock *sk = (struct sock *) arg;
@@ -92,6 +104,14 @@ static void l2cap_sock_timeout(unsigned long arg)
 
 	bh_lock_sock(sk);
 
+	if (sock_owned_by_user(sk)) {
+		/* sk is owned by user. Try again later */
+		l2cap_sock_set_timer(sk, HZ / 5);
+		bh_unlock_sock(sk);
+		sock_put(sk);
+		return;
+	}
+
 	if (sk->sk_state == BT_CONNECTED || sk->sk_state == BT_CONFIG)
 		reason = ECONNREFUSED;
 	else if (sk->sk_state == BT_CONNECT &&
@@ -108,18 +128,6 @@ static void l2cap_sock_timeout(unsigned long arg)
 	sock_put(sk);
 }
 
-static void l2cap_sock_set_timer(struct sock *sk, long timeout)
-{
-	BT_DBG("sk %p state %d timeout %ld", sk, sk->sk_state, timeout);
-	sk_reset_timer(sk, &sk->sk_timer, jiffies + timeout);
-}
-
-static void l2cap_sock_clear_timer(struct sock *sk)
-{
-	BT_DBG("sock %p state %d", sk, sk->sk_state);
-	sk_stop_timer(sk, &sk->sk_timer);
-}
-
 /* ---- L2CAP channels ---- */
 static struct sock *__l2cap_get_chan_by_dcid(struct l2cap_chan_list *l, u16 cid)
 {
-- 
1.7.0.4

Re: [PATCHv3 2/2] Bluetooth: timer check sk is not owned before freeing

[Gustavo F. Padovan]

Hi Andrei,

* Emeltchenko Andrei <Andrei.Emeltchenko.news@gmail.com> [2010-10-29 16:43:01 +0300]:

> From: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
> 
> In timer context we might delete l2cap channel used by krfcommd.
> The check makes sure that sk is not owned. If sk is owned we
> restart timer for HZ/5.
> 
> Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
> ---
>  net/bluetooth/l2cap.c |   32 ++++++++++++++++++++------------
>  1 files changed, 20 insertions(+), 12 deletions(-)
> 
> diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
> index b1344d8..c67b3c6 100644
> --- a/net/bluetooth/l2cap.c
> +++ b/net/bluetooth/l2cap.c
> @@ -83,6 +83,18 @@ static struct sk_buff *l2cap_build_cmd(struct l2cap_conn *conn,
>  static int l2cap_ertm_data_rcv(struct sock *sk, struct sk_buff *skb);
>  
>  /* ---- L2CAP timers ---- */
> +static void l2cap_sock_set_timer(struct sock *sk, long timeout)
> +{
> +	BT_DBG("sk %p state %d timeout %ld", sk, sk->sk_state, timeout);
> +	sk_reset_timer(sk, &sk->sk_timer, jiffies + timeout);
> +}
> +
> +static void l2cap_sock_clear_timer(struct sock *sk)
> +{
> +	BT_DBG("sock %p state %d", sk, sk->sk_state);
> +	sk_stop_timer(sk, &sk->sk_timer);
> +}
> +
>  static void l2cap_sock_timeout(unsigned long arg)
>  {
>  	struct sock *sk = (struct sock *) arg;
> @@ -92,6 +104,14 @@ static void l2cap_sock_timeout(unsigned long arg)
>  
>  	bh_lock_sock(sk);
>  
> +	if (sock_owned_by_user(sk)) {
> +		/* sk is owned by user. Try again later */
> +		l2cap_sock_set_timer(sk, HZ / 5);
> +		bh_unlock_sock(sk);
> +		sock_put(sk);

You can't do a sock_put() here, you have to keep the referencee to the
socket while the timer is enabled.

-- 
Gustavo F. Padovan
ProFUSION embedded systems - http://profusion.mobi

Re: [PATCHv3 2/2] Bluetooth: timer check sk is not owned before freeing

[Andrei Emeltchenko]

Hi Gustavo

On Sat, Oct 30, 2010 at 12:17 AM, Gustavo F. Padovan
<padovan@profusion.mobi> wrote:
> Hi Andrei,
>
> * Emeltchenko Andrei <Andrei.Emeltchenko.news@gmail.com> [2010-10-29 16:43:01 +0300]:
>
>> From: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
>>
>> In timer context we might delete l2cap channel used by krfcommd.
>> The check makes sure that sk is not owned. If sk is owned we
>> restart timer for HZ/5.
>>
>> Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
>> ---
>>  net/bluetooth/l2cap.c |   32 ++++++++++++++++++++------------
>>  1 files changed, 20 insertions(+), 12 deletions(-)
>>
>> diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
>> index b1344d8..c67b3c6 100644
>> --- a/net/bluetooth/l2cap.c
>> +++ b/net/bluetooth/l2cap.c
>> @@ -83,6 +83,18 @@ static struct sk_buff *l2cap_build_cmd(struct l2cap_conn *conn,
>>  static int l2cap_ertm_data_rcv(struct sock *sk, struct sk_buff *skb);
>>
>>  /* ---- L2CAP timers ---- */
>> +static void l2cap_sock_set_timer(struct sock *sk, long timeout)
>> +{
>> +     BT_DBG("sk %p state %d timeout %ld", sk, sk->sk_state, timeout);
>> +     sk_reset_timer(sk, &sk->sk_timer, jiffies + timeout);
>> +}
>> +
>> +static void l2cap_sock_clear_timer(struct sock *sk)
>> +{
>> +     BT_DBG("sock %p state %d", sk, sk->sk_state);
>> +     sk_stop_timer(sk, &sk->sk_timer);
>> +}
>> +
>>  static void l2cap_sock_timeout(unsigned long arg)
>>  {
>>       struct sock *sk = (struct sock *) arg;
>> @@ -92,6 +104,14 @@ static void l2cap_sock_timeout(unsigned long arg)
>>
>>       bh_lock_sock(sk);
>>
>> +     if (sock_owned_by_user(sk)) {
>> +             /* sk is owned by user. Try again later */
>> +             l2cap_sock_set_timer(sk, HZ / 5);
>> +             bh_unlock_sock(sk);
>> +             sock_put(sk);
>
> You can't do a sock_put() here, you have to keep the referencee to the
> socket while the timer is enabled.

sk_reset_timer is holding sock when timer restarts. The same way done
in TCP code in function:
static void tcp_delack_timer(unsigned long data)

Regards,
Andrei

Re: [PATCHv3 2/2] Bluetooth: timer check sk is not owned before freeing

[Gustavo F. Padovan]

Hi Andrei,

* Andrei Emeltchenko <andrei.emeltchenko.news@gmail.com> [2010-11-01 16:20:15 +0200]:

> Hi Gustavo
> 
> On Sat, Oct 30, 2010 at 12:17 AM, Gustavo F. Padovan
> <padovan@profusion.mobi> wrote:
> > Hi Andrei,
> >
> > * Emeltchenko Andrei <Andrei.Emeltchenko.news@gmail.com> [2010-10-29 16:43:01 +0300]:
> >
> >> From: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
> >>
> >> In timer context we might delete l2cap channel used by krfcommd.
> >> The check makes sure that sk is not owned. If sk is owned we
> >> restart timer for HZ/5.
> >>
> >> Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
> >> ---
> >>  net/bluetooth/l2cap.c |   32 ++++++++++++++++++++------------
> >>  1 files changed, 20 insertions(+), 12 deletions(-)
> >>
> >> diff --git a/net/bluetooth/l2cap.c b/net/bluetooth/l2cap.c
> >> index b1344d8..c67b3c6 100644
> >> --- a/net/bluetooth/l2cap.c
> >> +++ b/net/bluetooth/l2cap.c
> >> @@ -83,6 +83,18 @@ static struct sk_buff *l2cap_build_cmd(struct l2cap_conn *conn,
> >>  static int l2cap_ertm_data_rcv(struct sock *sk, struct sk_buff *skb);
> >>
> >>  /* ---- L2CAP timers ---- */
> >> +static void l2cap_sock_set_timer(struct sock *sk, long timeout)
> >> +{
> >> +     BT_DBG("sk %p state %d timeout %ld", sk, sk->sk_state, timeout);
> >> +     sk_reset_timer(sk, &sk->sk_timer, jiffies + timeout);
> >> +}
> >> +
> >> +static void l2cap_sock_clear_timer(struct sock *sk)
> >> +{
> >> +     BT_DBG("sock %p state %d", sk, sk->sk_state);
> >> +     sk_stop_timer(sk, &sk->sk_timer);
> >> +}
> >> +
> >>  static void l2cap_sock_timeout(unsigned long arg)
> >>  {
> >>       struct sock *sk = (struct sock *) arg;
> >> @@ -92,6 +104,14 @@ static void l2cap_sock_timeout(unsigned long arg)
> >>
> >>       bh_lock_sock(sk);
> >>
> >> +     if (sock_owned_by_user(sk)) {
> >> +             /* sk is owned by user. Try again later */
> >> +             l2cap_sock_set_timer(sk, HZ / 5);
> >> +             bh_unlock_sock(sk);
> >> +             sock_put(sk);
> >
> > You can't do a sock_put() here, you have to keep the referencee to the
> > socket while the timer is enabled.
> 
> sk_reset_timer is holding sock when timer restarts. The same way done
> in TCP code in function:
> static void tcp_delack_timer(unsigned long data)

Yes, I got confused, you're right.

-- 
Gustavo F. Padovan
ProFUSION embedded systems - http://profusion.mobi