Re: [PATCHv2] Bluetooth: Prevent uninitialized data access in L2CAP configuration

[Marcel Holtmann <marcel@holtmann.org>]

Hi Mat,

> When configuring an ERTM or streaming mode connection, remote devices
> are expected to send an RFC option in a successful config response.  A
> misbehaving remote device might not send an RFC option, and the L2CAP
> code should not access uninitialized data in this case.
> 
> Signed-off-by: Mat Martineau <mathewm@codeaurora.org>
> ---
>  net/bluetooth/l2cap_core.c |   11 ++++++++++-
>  1 files changed, 10 insertions(+), 1 deletions(-)
> 
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 5ea94a1..45dd423 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -2152,7 +2152,7 @@ static int l2cap_parse_conf_rsp(struct l2cap_chan *chan, void *rsp, int len, voi
>  	void *ptr = req->data;
>  	int type, olen;
>  	unsigned long val;
> -	struct l2cap_conf_rfc rfc;
> +	struct l2cap_conf_rfc rfc = { .mode = L2CAP_MODE_BASIC };
>  
>  	BT_DBG("chan %p, rsp %p, len %d, req %p", chan, rsp, len, data);
>  
> @@ -2271,6 +2271,15 @@ static void l2cap_conf_rfc_get(struct l2cap_chan *chan, void *rsp, int len)
>  		}
>  	}
>  
> +	/* Use sane default values in case a misbehaving remote device
> +	 * did not send an RFC option.
> +	 */
> +	BT_ERR("Expected RFC option was not found, using defaults");
> +	rfc.mode = chan->mode;
> +	rfc.retrans_timeout = cpu_to_le16(L2CAP_DEFAULT_RETRANS_TO);
> +	rfc.monitor_timeout = cpu_to_le16(L2CAP_DEFAULT_MONITOR_TO);
> +	rfc.max_pdu_size = cpu_to_le16(chan->imtu);

I would actually put the BT_ERR afterwards the assignments separated
with an extra empty line, but that is just to make it a bit easier on
the eyes.

> +
>  done:
>  	switch (rfc.mode) {
>  	case L2CAP_MODE_ERTM:

Acked-by: Marcel Holtmann <marcel@holtmann.org>

Regards

Marcel