Subject: Re: Bluetooth: Prevent stack info leak from the EFS element.

From: Guenter Roeck <[email-masked]>
Date: Tue, 2 Jan 2018 12:26:15 -0800

On Fri, Dec 08, 2017 at 03:14:47PM +0100, [email-masked] wrote:
> From: Ben Seri <[email-masked]>
> 
> In the function l2cap_parse_conf_rsp and in the function
> l2cap_parse_conf_req the following variable is declared without
> initialization:
> 
> struct l2cap_conf_efs efs;
> 
> In addition, when parsing input configuration parameters in both of
> these functions, the switch case for handling EFS elements may skip the
> memcpy call that will write to the efs variable:
> 
> ...
> case L2CAP_CONF_EFS:
> if (olen == sizeof(efs))
> memcpy(&efs, (void *)val, olen);
> ...
> 
> The olen in the above if is attacker controlled, and regardless of that
> if, in both of these functions the efs variable would eventually be
> added to the outgoing configuration request that is being built:
> 
> l2cap_add_conf_opt(&ptr, L2CAP_CONF_EFS, sizeof(efs), (unsigned long) &efs);
> 
> So by sending a configuration request, or response, that contains an
> L2CAP_CONF_EFS element, but with an element length that is not
> sizeof(efs) - the memcpy to the uninitialized efs variable can be
> avoided, and the uninitialized variable would be returned to the
> attacker (16 bytes).
> 
> This issue has been assigned CVE-2017-1000410
> 
> Cc: Marcel Holtmann <[email-masked]>
> Cc: Gustavo Padovan <[email-masked]>
> Cc: Johan Hedberg <[email-masked]>
> Cc: stable <[email-masked]>
> Signed-off-by: Ben Seri <[email-masked]>
> Signed-off-by: Greg Kroah-Hartman <[email-masked]>
> ---
>  net/bluetooth/l2cap_core.c |   20 +++++++++++---------
>  1 file changed, 11 insertions(+), 9 deletions(-)
> 
> Marcel, for some reason this patch never got applied, despite lots of
> advance notice.  Please, someone queue it up as it resolves the above
> very-well-reported issue.
> 

This patch is still not upstream or in -next. Given that we (ChromeOS)
are heavy Bluetooth users, I'll go ahead and apply it without waiting
any longer. For my understanding and for tracking purposes, it would
be useful to know why it is not being applied. Does anyone know ?

Thanks,
Guenter

> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 43ba91c440bc..fc6615d59165 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -3363,9 +3363,10 @@ static int l2cap_parse_conf_req(struct l2cap_chan *chan, void *data, size_t data
>  			break;
>  
>  		case L2CAP_CONF_EFS:
> -			remote_efs = 1;
> -			if (olen == sizeof(efs))
> +			if (olen == sizeof(efs)) {
> +				remote_efs = 1;
>  				memcpy(&efs, (void *) val, olen);
> +			}
>  			break;
>  
>  		case L2CAP_CONF_EWS:
> @@ -3584,16 +3585,17 @@ static int l2cap_parse_conf_rsp(struct l2cap_chan *chan, void *rsp, int len,
>  			break;
>  
>  		case L2CAP_CONF_EFS:
> -			if (olen == sizeof(efs))
> +			if (olen == sizeof(efs)) {
>  				memcpy(&efs, (void *)val, olen);
>  
> -			if (chan->local_stype != L2CAP_SERV_NOTRAFIC &&
> -			    efs.stype != L2CAP_SERV_NOTRAFIC &&
> -			    efs.stype != chan->local_stype)
> -				return -ECONNREFUSED;
> +				if (chan->local_stype != L2CAP_SERV_NOTRAFIC &&
> +				    efs.stype != L2CAP_SERV_NOTRAFIC &&
> +				    efs.stype != chan->local_stype)
> +					return -ECONNREFUSED;
>  
> -			l2cap_add_conf_opt(&ptr, L2CAP_CONF_EFS, sizeof(efs),
> -					   (unsigned long) &efs, endptr - ptr);
> +				l2cap_add_conf_opt(&ptr, L2CAP_CONF_EFS, sizeof(efs),
> +						   (unsigned long) &efs, endptr - ptr);
> +			}
>  			break;
>  
>  		case L2CAP_CONF_FCS: