Patch "Bluetooth: Prevent stack info leak from the EFS element." has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

Bluetooth: Prevent stack info leak from the EFS element.

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
bluetooth-prevent-stack-info-leak-from-the-efs-element.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Ben Seri <[email protected]>
Date: Fri, 8 Dec 2017 15:14:47 +0100
Subject: Bluetooth: Prevent stack info leak from the EFS element.

From: Ben Seri <[email protected]>

commit 06e7e776ca4d36547e503279aeff996cbb292c16 upstream.

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

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

@@ -3342,9 +3342,10 @@ static int l2cap_parse_conf_req(struct l
 			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:

@@ -3563,16 +3564,17 @@ static int l2cap_parse_conf_rsp(struct l
 			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:

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/bluetooth-prevent-stack-info-leak-from-the-efs-element.patch