From: Brian Gix <bgix@codeaurora.org>
To: Andrei Emeltchenko <andrei.emeltchenko.news@gmail.com>,
linux-bluetooth@vger.kernel.org
Subject: Re: [PATCH-v7 1/2] Bluetooth: Add MITM mechanism to LE-SMP
Date: Wed, 21 Dec 2011 10:11:06 -0800 [thread overview]
Message-ID: <4EF2213A.7030007@codeaurora.org> (raw)
In-Reply-To: <20111221102841.GB21295@aemeltch-MOBL1>
Hi Andrei,
On 12/21/2011 2:28 AM, Andrei Emeltchenko wrote:
> Hi Brian,
>
> On Tue, Dec 20, 2011 at 05:04:41PM -0800, Brian Gix wrote:
>> To achive Man-In-The-Middle (MITM) level security with Low Energy,
>> we have to enable User Passkey Comparison. This commit modifies the
>> hard-coded JUST-WORKS pairing mechanism to support query via the MGMT
>> interface of Passkey comparison and User Confirmation.
>>
>> Signed-off-by: Brian Gix<bgix@codeaurora.org>
>> ---
>> include/net/bluetooth/hci_core.h | 1 +
>> include/net/bluetooth/smp.h | 5 +
>> net/bluetooth/smp.c | 227 ++++++++++++++++++++++++++++++++++----
>> 3 files changed, 211 insertions(+), 22 deletions(-)
>
> ...
>
>> +static int tk_request(struct l2cap_conn *conn, u8 remote_oob, u8 auth,
>> + u8 local_io, u8 remote_io)
>> +{
>> + struct hci_conn *hcon = conn->hcon;
>> + struct smp_chan *smp = conn->smp_chan;
>> + u8 method;
>> + u32 passkey = 0;
>> + int ret = 0;
>> +
>> + /* Initialize key to JUST WORKS */
>> + memset(smp->tk, 0, sizeof(smp->tk));
>> + clear_bit(SMP_FLAG_TK_VALID,&smp->smp_flags);
>> +
>> + BT_DBG("tk_request: auth:%d lcl:%d rem:%d", auth, local_io, remote_io);
>> +
>> + /* If neither side wants MITM, use JUST WORKS */
>> + /* If either side has unknown io_caps, use JUST_WORKS */
>> + if (!(auth& SMP_AUTH_MITM) ||
>> + local_io> SMP_IO_KEYBOARD_DISPLAY ||
>> + remote_io> SMP_IO_KEYBOARD_DISPLAY) {
>> + auth&= ~SMP_AUTH_MITM;
>> + set_bit(SMP_FLAG_TK_VALID,&smp->smp_flags);
>> + return 0;
>> + }
>> +
>> + /* MITM is now officially requested, but not required */
>> + /* Determine what we need (if anything) from the agent */
>> + method = gen_method[local_io][remote_io];
>> +
>> + if (method == JUST_WORKS || method == JUST_CFM)
>> + auth&= ~SMP_AUTH_MITM;
>> +
>> + /* Don't bother confirming unbonded JUST_WORKS */
>> + if (!(auth& SMP_AUTH_BONDING)&& method == JUST_CFM) {
>> + set_bit(SMP_FLAG_TK_VALID,&smp->smp_flags);
>> + return 0;
>> + } else if (method == JUST_WORKS) {
>> + set_bit(SMP_FLAG_TK_VALID,&smp->smp_flags);
>> + return 0;
>> + } else if (method == OVERLAP) {
>> + if (hcon->link_mode& HCI_LM_MASTER)
>> + method = CFM_PASSKEY;
>> + else
>> + method = REQ_PASSKEY;
>> + }
>> +
>> + if (method == CFM_PASSKEY) {
>> + u8 key[16];
>> + /* Generate a passkey for display. It is not valid until
>> + * confirmed.
>> + */
>> + memset(key, 0, sizeof(key));
>> + get_random_bytes(&passkey, sizeof(passkey));
>> + passkey %= 1000000;
>> + put_unaligned_le32(passkey, key);
>> + swap128(key, smp->tk);
>> + BT_DBG("PassKey: %d", passkey);
>> + }
>
> Would it make sense to use switch(method) instead of [if/else/else if] ?
I can use a simpler "method" switch at the end, to determine which mgmt
call to make to get the passkey or confirmation. However, the "truth
table" is a bit too complex for a switch, with the method being tweaked
based on rules coming from the Core Spec, and then later clarified in
erratum 4249. I also wanted to avoid putting the random passkey
generation inside of the hci_dev_lock block.
--
Brian Gix
bgix@codeaurora.org
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
next prev parent reply other threads:[~2011-12-21 18:11 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-21 1:04 [PATCH-v7 0/2] Bluetooth: Add MITM protection to LE-SMP Brian Gix
2011-12-21 1:04 ` [PATCH-v7 1/2] Bluetooth: Add MITM mechanism " Brian Gix
2011-12-21 2:22 ` Marcel Holtmann
2011-12-21 10:28 ` Andrei Emeltchenko
2011-12-21 18:11 ` Brian Gix [this message]
2011-12-21 19:50 ` Marcel Holtmann
2011-12-21 1:04 ` [PATCH-v7 2/2] Bluetooth: Add SMP to User Passkey and Confirm Brian Gix
2011-12-21 2:26 ` Marcel Holtmann
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