netdev - Re: [PATCH 2/2] Bluetooth: check the buffer size for some messages before parsing

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Message-Id: <8D42DA95-47AB-47B0-B8A5-0F7FF8C786E4@holtmann.org>
Date:   Fri, 18 Jan 2019 12:11:01 +0100
From:   Marcel Holtmann <marcel@...tmann.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Johan Hedberg <johan.hedberg@...il.com>,
        linux-bluetooth@...r.kernel.org, netdev@...r.kernel.org,
        Ran Menscher <ran.menscher@...ambasecurity.com>
Subject: Re: [PATCH 2/2] Bluetooth: check the buffer size for some messages
 before parsing

Hi Greg,

>>> The L2CAP_CONF_EFS and L2CAP_CONF_RFC messages can be sent from
>>> userspace so their structure sizes need to be checked before parsing
>>> them.
>> 
>> this message is confusing me. How can these be send from userspace?
> 
> So claimed the original reporter.  You have the information in your
> inbox, is it incorrect?

I am pretty sure he meant that the remote attacker can control it from userspace. This is still a wire protocol and not some socket options.

>>> 
>>> Based on a patch from Ran Menscher.
>>> 
>>> Reported-by: Ran Menscher <ran.menscher@...ambasecurity.com>
>>> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>> ---
>>> net/bluetooth/l2cap_core.c | 12 ++++++++----
>>> 1 file changed, 8 insertions(+), 4 deletions(-)
>>> 
>>> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
>>> index 93daf94565cf..55e48e6efc2b 100644
>>> --- a/net/bluetooth/l2cap_core.c
>>> +++ b/net/bluetooth/l2cap_core.c
>>> @@ -3361,7 +3361,8 @@ static int l2cap_parse_conf_req(struct l2cap_chan *chan, void *data, size_t data
>>> 			break;
>>> 
>>> 		case L2CAP_CONF_RFC:
>>> -			if (olen == sizeof(rfc))
>>> +			if ((olen == sizeof(rfc)) &&
>>> +			    (endptr - ptr >= L2CAP_CONF_OPT_SIZE + sizeof(rfc)))
>>> 				memcpy(&rfc, (void *) val, olen);
>> 
>> We don’t do ((x == y) && (..)) actually. Using (x == y && ..) is plenty.
> 
> Ick, ok, whatever, you all trust that your brains can remember C
> priority levels, me, I trust ()...
> 
> I can fix this up to remove the extra (), but I would like _SOMEONE_ to
> at least validate that this resolves the reported issues…

I need to reproduce this and then I can tell you.

Regards

Marcel