Re: [PATCH] Bluetooth: Fix potential NULL pointer dereference in L2CAP

[Andrei Emeltchenko <andrei.emeltchenko.news@gmail.com>]

Hi Johan,

On Tue, Jun 05, 2012 at 02:20:41PM +0800, Johan Hedberg wrote:
> From: Johan Hedberg <johan.hedberg@intel.com>
> 
> In the following scenario conn->hchan is not set when l2cap_conn_del is
> called:
> 
> < HCI Command: LE Create Connection (0x08|0x000d) plen 25
>     bdaddr xx:xx:xx:xx:xx:xx type 0
> > HCI Event: Command Status (0x0f) plen 4
>     LE Create Connection (0x08|0x000d) status 0x00 ncmd 1
> > HCI Event: LE Meta Event (0x3e) plen 19
>     LE Connection Complete
>       status 0x00 handle 64, role master
>       bdaddr xx:xx:xx:xx:xx:xx (Public)
> < ACL data: handle 64 flags 0x00 dlen 11
>     SMP: Pairing Request (0x01)
>       capability 0x04 oob 0x00 auth req 0x01
>       max key size 0x10 init key dist 0x00 resp key dist 0x01
>       Capability: KeyboardDisplay (OOB data not present)
>       Authentication: Bonding (No MITM Protection)
>       Initiator Key Distribution:
>       Responder Key Distribution:  LTK
> > HCI Event: Number of Completed Packets (0x13) plen 5
>     handle 64 packets 1
> < HCI Command: Disconnect (0x01|0x0006) plen 3
>     handle 64 reason 0x13
>     Reason: Remote User Terminated Connection
> > HCI Event: Command Status (0x0f) plen 4
>     Disconnect (0x01|0x0006) status 0x00 ncmd 1
> > HCI Event: Disconn Complete (0x05) plen 4
>     status 0x00 handle 64 reason 0x22
>     Reason: LMP Response Timeout
> 
> This results in the following crash:
> 
> BUG: unable to handle kernel NULL pointer dereference at 00000004
> IP: [<c123f9e5>] hci_chan_del+0x41/0x6e
> *pde = 00000000
> Oops: 0002 [#1] SMP
> Modules linked in:
> 
> Pid: 32, comm: kworker/u:3 Not tainted 3.5.0-rc1+ #322 Bochs Bochs
> EIP: 0060:[<c123f9e5>] EFLAGS: 00010246 CPU: 1
> EIP is at hci_chan_del+0x41/0x6e
> EAX: 00200909 EBX: f5dd2280 ECX: 00000000 EDX: 00000000
> ESI: f5d5edc4 EDI: f6201e60 EBP: f6201e50 ESP: f6201e48
>  DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
> CR0: 8005003b CR2: 00000004 CR3: 35f12000 CR4: 00000690
> DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
> DR6: ffff0ff0 DR7: 00000400
> Process kworker/u:3 (pid: 32, ti=f6200000 task=f686e730 task.ti=f6200000)
> Stack:
>  f5d5ef00 f6201e60 f6201e88 c12507b3 f62e6000 c12507b3 c1245fad 0000000c
>  f5d5ef94 00000026 f5d5ef9c f5d5edc4 f6917800 f62e6000 00000022 f6201e98
>  f6201ea8 c125440b f6201eb8 c125440b c124963d f6254622 f62e6000 f6201eb8
> Call Trace:
>  [<c12507b3>] l2cap_conn_del+0xef/0x135
>  [<c12507b3>] ? l2cap_conn_del+0xef/0x135
>  [<c1245fad>] ? mgmt_event+0x95/0xa6
>  [<c125440b>] l2cap_disconn_cfm+0x49/0x57
>  [<c125440b>] ? l2cap_disconn_cfm+0x49/0x57
>  [<c124963d>] ? user_confirm_reply+0x7d/0x7d
>  [<c124446c>] hci_event_packet+0x33e/0x1cce
>  [<c124446c>] ? hci_event_packet+0x33e/0x1cce
>  [<c11e1aaa>] ? __kfree_skb+0x6a/0x6d
>  [<c11e1af9>] ? kfree_skb+0x25/0x27
>  [<c124be14>] ? hci_send_to_sock+0x168/0x174
>  [<c123b66c>] hci_rx_work+0xf3/0x347
>  [<c123b66c>] ? hci_rx_work+0xf3/0x347
>  [<c123b9a7>] ? hci_cmd_work+0xb4/0xd8
> 
> This patch fixes this issue by adding a NULL check for conn->hchan.
> 
> Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
> ---
>  net/bluetooth/l2cap_core.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index f9bffe3..62df491 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -1295,7 +1295,8 @@ static void l2cap_conn_del(struct hci_conn *hcon, int err)
>  
>  	mutex_unlock(&conn->chan_lock);
>  
> -	hci_chan_del(conn->hchan);
> +	if (conn->hchan)
> +		hci_chan_del(conn->hchan);

Is this SMP - related bug? Shall we check rather for LE/SMP stuff?

Best regards 
Andrei Emeltchenko