[PATCH] Bluetooth: Check L2CAP option sizes returned from l2cap_get_conf_opt

[PATCH] Bluetooth: Check L2CAP option sizes returned from l2cap_get_conf_opt

[Marcel Holtmann]

When doing option parsing for standard type values of 1, 2 or 4 octets,
the value is converted directly into a variable instead of a pointer. To
avoid being tricked into being a pointer, check that for these option
types that sizes actually match. In L2CAP every option is fixed size and
thus it is prudent anyway to ensure that the remote side sends us the
right option size along with option paramters.

If the option size is not matching the option type, then that option is
silently ignored. It is a protocol violation and instead of trying to
give the remote attacker any further hints just pretend that option is
not present and proceed with the default values. Implementation
following the specification and its qualification procedures will always
use the correct size and thus not being impacted here.

To keep the code readable and consistent accross all options, a few
cosmetic changes were also required.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
---
 net/bluetooth/l2cap_core.c | 77 +++++++++++++++++++++++---------------
 1 file changed, 46 insertions(+), 31 deletions(-)

diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
index 2a7fb517d460..77799e7d5a34 100644
--- a/net/bluetooth/l2cap_core.c
+++ b/net/bluetooth/l2cap_core.c
@@ -3343,10 +3343,14 @@ static int l2cap_parse_conf_req(struct l2cap_chan *chan, void *data, size_t data
 
 		switch (type) {
 		case L2CAP_CONF_MTU:
+			if (olen != 2)
+				break;
 			mtu = val;
 			break;
 
 		case L2CAP_CONF_FLUSH_TO:
+			if (olen != 2)
+				break;
 			chan->flush_to = val;
 			break;
 
@@ -3354,26 +3358,30 @@ static int l2cap_parse_conf_req(struct l2cap_chan *chan, void *data, size_t data
 			break;
 
 		case L2CAP_CONF_RFC:
-			if (olen == sizeof(rfc))
-				memcpy(&rfc, (void *) val, olen);
+			if (olen != sizeof(rfc))
+				break;
+			memcpy(&rfc, (void *) val, olen);
 			break;
 
 		case L2CAP_CONF_FCS:
+			if (olen != 1)
+				break;
 			if (val == L2CAP_FCS_NONE)
 				set_bit(CONF_RECV_NO_FCS, &chan->conf_state);
 			break;
 
 		case L2CAP_CONF_EFS:
-			if (olen == sizeof(efs)) {
-				remote_efs = 1;
-				memcpy(&efs, (void *) val, olen);
-			}
+			if (olen != sizeof(efs))
+				break;
+			remote_efs = 1;
+			memcpy(&efs, (void *) val, olen);
 			break;
 
 		case L2CAP_CONF_EWS:
+			if (olen != 2)
+				break;
 			if (!(chan->conn->local_fixed_chan & L2CAP_FC_A2MP))
 				return -ECONNREFUSED;
-
 			set_bit(FLAG_EXT_CTRL, &chan->flags);
 			set_bit(CONF_EWS_RECV, &chan->conf_state);
 			chan->tx_win_max = L2CAP_DEFAULT_EXT_WINDOW;
@@ -3383,7 +3391,6 @@ static int l2cap_parse_conf_req(struct l2cap_chan *chan, void *data, size_t data
 		default:
 			if (hint)
 				break;
-
 			result = L2CAP_CONF_UNKNOWN;
 			*((u8 *) ptr++) = type;
 			break;
@@ -3551,55 +3558,60 @@ static int l2cap_parse_conf_rsp(struct l2cap_chan *chan, void *rsp, int len,
 
 		switch (type) {
 		case L2CAP_CONF_MTU:
+			if (olen != 2)
+				break;
 			if (val < L2CAP_DEFAULT_MIN_MTU) {
 				*result = L2CAP_CONF_UNACCEPT;
 				chan->imtu = L2CAP_DEFAULT_MIN_MTU;
 			} else
 				chan->imtu = val;
-			l2cap_add_conf_opt(&ptr, L2CAP_CONF_MTU, 2, chan->imtu, endptr - ptr);
+			l2cap_add_conf_opt(&ptr, L2CAP_CONF_MTU, 2, chan->imtu,
+					   endptr - ptr);
 			break;
 
 		case L2CAP_CONF_FLUSH_TO:
+			if (olen != 2)
+				break;
 			chan->flush_to = val;
-			l2cap_add_conf_opt(&ptr, L2CAP_CONF_FLUSH_TO,
-					   2, chan->flush_to, endptr - ptr);
+			l2cap_add_conf_opt(&ptr, L2CAP_CONF_FLUSH_TO, 2,
+					   chan->flush_to, endptr - ptr);
 			break;
 
 		case L2CAP_CONF_RFC:
-			if (olen == sizeof(rfc))
-				memcpy(&rfc, (void *)val, olen);
-
+			if (olen != sizeof(rfc))
+				break;
+			memcpy(&rfc, (void *)val, olen);
 			if (test_bit(CONF_STATE2_DEVICE, &chan->conf_state) &&
 			    rfc.mode != chan->mode)
 				return -ECONNREFUSED;
-
 			chan->fcs = 0;
-
-			l2cap_add_conf_opt(&ptr, L2CAP_CONF_RFC,
-					   sizeof(rfc), (unsigned long) &rfc, endptr - ptr);
+			l2cap_add_conf_opt(&ptr, L2CAP_CONF_RFC, sizeof(rfc),
+					   (unsigned long) &rfc, endptr - ptr);
 			break;
 
 		case L2CAP_CONF_EWS:
+			if (olen != 2)
+				break;
 			chan->ack_win = min_t(u16, val, chan->ack_win);
 			l2cap_add_conf_opt(&ptr, L2CAP_CONF_EWS, 2,
 					   chan->tx_win, endptr - ptr);
 			break;
 
 		case L2CAP_CONF_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;
-
-				l2cap_add_conf_opt(&ptr, L2CAP_CONF_EFS, sizeof(efs),
-						   (unsigned long) &efs, endptr - ptr);
-			}
+			if (olen != sizeof(efs))
+				break;
+			memcpy(&efs, (void *)val, olen);
+			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);
 			break;
 
 		case L2CAP_CONF_FCS:
+			if (olen != 1)
+				break;
 			if (*result == L2CAP_CONF_PENDING)
 				if (val == L2CAP_FCS_NONE)
 					set_bit(CONF_RECV_NO_FCS,
@@ -3731,10 +3743,13 @@ static void l2cap_conf_rfc_get(struct l2cap_chan *chan, void *rsp, int len)
 
 		switch (type) {
 		case L2CAP_CONF_RFC:
-			if (olen == sizeof(rfc))
-				memcpy(&rfc, (void *)val, olen);
+			if (olen != sizeof(rfc))
+				break;
+			memcpy(&rfc, (void *)val, olen);
 			break;
 		case L2CAP_CONF_EWS:
+			if (olen != 2)
+				break;
 			txwin_ext = val;
 			break;
 		}
-- 
2.20.1

Re: [PATCH] Bluetooth: Check L2CAP option sizes returned from l2cap_get_conf_opt

[Greg KH]

On Fri, Jan 18, 2019 at 12:56:20PM +0100, Marcel Holtmann wrote:
> When doing option parsing for standard type values of 1, 2 or 4 octets,
> the value is converted directly into a variable instead of a pointer. To
> avoid being tricked into being a pointer, check that for these option
> types that sizes actually match. In L2CAP every option is fixed size and
> thus it is prudent anyway to ensure that the remote side sends us the
> right option size along with option paramters.
> 
> If the option size is not matching the option type, then that option is
> silently ignored. It is a protocol violation and instead of trying to
> give the remote attacker any further hints just pretend that option is
> not present and proceed with the default values. Implementation
> following the specification and its qualification procedures will always
> use the correct size and thus not being impacted here.
> 
> To keep the code readable and consistent accross all options, a few
> cosmetic changes were also required.

Ah, that's a much nicer patch than mine, I like it.  As long as the code
for handling things when an option is not set properly works ok (which
I'm guessing it is as that would have been found out long ago), this
makes everything much simpler.

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

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Re: [PATCH] Bluetooth: Check L2CAP option sizes returned from l2cap_get_conf_opt

[Marcel Holtmann]

Hi Greg,

>> When doing option parsing for standard type values of 1, 2 or 4 octets,
>> the value is converted directly into a variable instead of a pointer. To
>> avoid being tricked into being a pointer, check that for these option
>> types that sizes actually match. In L2CAP every option is fixed size and
>> thus it is prudent anyway to ensure that the remote side sends us the
>> right option size along with option paramters.
>> 
>> If the option size is not matching the option type, then that option is
>> silently ignored. It is a protocol violation and instead of trying to
>> give the remote attacker any further hints just pretend that option is
>> not present and proceed with the default values. Implementation
>> following the specification and its qualification procedures will always
>> use the correct size and thus not being impacted here.
>> 
>> To keep the code readable and consistent accross all options, a few
>> cosmetic changes were also required.
> 
> Ah, that's a much nicer patch than mine, I like it.  As long as the code
> for handling things when an option is not set properly works ok (which
> I'm guessing it is as that would have been found out long ago), this
> makes everything much simpler.

we treat it as the option would not be present and that is allowed since Bluetooth 1.0b and works just fine.

Regards

Marcel

Re: [PATCH] Bluetooth: Check L2CAP option sizes returned from l2cap_get_conf_opt

[Johan Hedberg]

Hi Marcel,

On Fri, Jan 18, 2019, Marcel Holtmann wrote:
> When doing option parsing for standard type values of 1, 2 or 4 octets,
> the value is converted directly into a variable instead of a pointer. To
> avoid being tricked into being a pointer, check that for these option
> types that sizes actually match. In L2CAP every option is fixed size and
> thus it is prudent anyway to ensure that the remote side sends us the
> right option size along with option paramters.
> 
> If the option size is not matching the option type, then that option is
> silently ignored. It is a protocol violation and instead of trying to
> give the remote attacker any further hints just pretend that option is
> not present and proceed with the default values. Implementation
> following the specification and its qualification procedures will always
> use the correct size and thus not being impacted here.
> 
> To keep the code readable and consistent accross all options, a few
> cosmetic changes were also required.
> 
> Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
> ---
>  net/bluetooth/l2cap_core.c | 77 +++++++++++++++++++++++---------------
>  1 file changed, 46 insertions(+), 31 deletions(-)

Applied to bluetooth-next. Thanks.

Johan