[PATCH RESEND] Bluetooth: Prevent stack info leak from the EFS element.

[Greg Kroah-Hartman]

From: Ben Seri <ben@xxxxxxxxx>

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 <marcel@xxxxxxxxxxxx>
Cc: Gustavo Padovan <gustavo@xxxxxxxxxxx>
Cc: Johan Hedberg <johan.hedberg@xxxxxxxxx>
Cc: stable <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Ben Seri <ben@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 net/bluetooth/l2cap_core.c |   20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

David, can you take this through your tree?  It fixes a reported issue
and the bluetooth developers seem to be totally ignoring it for weeks
for some unknown reason :(

Or, I can take it through one of mine if you don't want to touch it.

thanks,

greg k-h

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: