[PATCH] Bluetooth: hci_core: Avoid mixing up req_complete and req_complete_skb

[PATCH] Bluetooth: hci_core: Avoid mixing up req_complete and req_complete_skb

[Douglas Anderson]

In commit 44d271377479 ("Bluetooth: Compress the size of struct
hci_ctrl") we squashed down the size of the structure by using a union
with the assumption that all users would use the flag to determine
whether we had a req_complete or a req_complete_skb.

Unfortunately we had a case in hci_req_cmd_complete() where we weren't
looking at the flag.  This can result in a situation where we might be
storing a hci_req_complete_skb_t in a hci_req_complete_t variable, or
vice versa.

During some testing I found at least one case where the function
hci_req_sync_complete() was called improperly because the kernel thought
that it didn't require an SKB.  Looking through the stack in kgdb I
found that it was called by hci_event_packet() and that
hci_event_packet() had both of its locals "req_complete" and
"req_complete_skb" pointing to the same place: both to
hci_req_sync_complete().

Let's make sure we always check the flag.

For more details on debugging done, see <http://crbug.com/588288>.

Fixes: 44d271377479 ("Bluetooth: Compress the size of struct hci_ctrl")
Signed-off-by: Douglas Anderson <dianders-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
---
Testing was done on a Chrome OS device on kernel 3.14 w/
bluetooth-next backports.  Since I couldn't reliably reproduce the
problem, I simply confirmed that existing functionality worked.

 net/bluetooth/hci_core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
index 541760fe53d4..9c0a6830ff92 100644
--- a/net/bluetooth/hci_core.c
+++ b/net/bluetooth/hci_core.c
@@ -4118,8 +4118,10 @@ void hci_req_cmd_complete(struct hci_dev *hdev, u16 opcode, u8 status,
 			break;
 		}
 
-		*req_complete = bt_cb(skb)->hci.req_complete;
-		*req_complete_skb = bt_cb(skb)->hci.req_complete_skb;
+		if (bt_cb(skb)->hci.req_flags & HCI_REQ_SKB)
+			*req_complete_skb = bt_cb(skb)->hci.req_complete_skb;
+		else
+			*req_complete = bt_cb(skb)->hci.req_complete;
 		kfree_skb(skb);
 	}
 	spin_unlock_irqrestore(&hdev->cmd_q.lock, flags);
-- 
2.7.0.rc3.207.g0ac5344

Re: [PATCH] Bluetooth: hci_core: Avoid mixing up req_complete and req_complete_skb

[Johan Hedberg]

Hi Douglas,

On Fri, Feb 19, 2016, Douglas Anderson wrote:
> In commit 44d271377479 ("Bluetooth: Compress the size of struct
> hci_ctrl") we squashed down the size of the structure by using a union
> with the assumption that all users would use the flag to determine
> whether we had a req_complete or a req_complete_skb.
> 
> Unfortunately we had a case in hci_req_cmd_complete() where we weren't
> looking at the flag.  This can result in a situation where we might be
> storing a hci_req_complete_skb_t in a hci_req_complete_t variable, or
> vice versa.
> 
> During some testing I found at least one case where the function
> hci_req_sync_complete() was called improperly because the kernel thought
> that it didn't require an SKB.  Looking through the stack in kgdb I
> found that it was called by hci_event_packet() and that
> hci_event_packet() had both of its locals "req_complete" and
> "req_complete_skb" pointing to the same place: both to
> hci_req_sync_complete().
> 
> Let's make sure we always check the flag.
> 
> For more details on debugging done, see <http://crbug.com/588288>.
> 
> Fixes: 44d271377479 ("Bluetooth: Compress the size of struct hci_ctrl")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> Testing was done on a Chrome OS device on kernel 3.14 w/
> bluetooth-next backports.  Since I couldn't reliably reproduce the
> problem, I simply confirmed that existing functionality worked.
> 
>  net/bluetooth/hci_core.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)

Good catch.

Acked-by: Johan Hedberg <johan.hedberg@intel.com>

Marcel, I think we want to send this through our stable tree to 4.5-rc
(where the patch introducing the bug is).

Johan

Re: [PATCH] Bluetooth: hci_core: Avoid mixing up req_complete and req_complete_skb

[Marcel Holtmann]

Hi Douglas,

> In commit 44d271377479 ("Bluetooth: Compress the size of struct
> hci_ctrl") we squashed down the size of the structure by using a union
> with the assumption that all users would use the flag to determine
> whether we had a req_complete or a req_complete_skb.
> 
> Unfortunately we had a case in hci_req_cmd_complete() where we weren't
> looking at the flag.  This can result in a situation where we might be
> storing a hci_req_complete_skb_t in a hci_req_complete_t variable, or
> vice versa.
> 
> During some testing I found at least one case where the function
> hci_req_sync_complete() was called improperly because the kernel thought
> that it didn't require an SKB.  Looking through the stack in kgdb I
> found that it was called by hci_event_packet() and that
> hci_event_packet() had both of its locals "req_complete" and
> "req_complete_skb" pointing to the same place: both to
> hci_req_sync_complete().
> 
> Let's make sure we always check the flag.
> 
> For more details on debugging done, see <http://crbug.com/588288>.
> 
> Fixes: 44d271377479 ("Bluetooth: Compress the size of struct hci_ctrl")
> Signed-off-by: Douglas Anderson <dianders@chromium.org>
> ---
> Testing was done on a Chrome OS device on kernel 3.14 w/
> bluetooth-next backports.  Since I couldn't reliably reproduce the
> problem, I simply confirmed that existing functionality worked.
> 
> net/bluetooth/hci_core.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)

patch has been applied to bluetooth-stable tree.

Regards

Marcel