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@xxxxxxxxxxxxxx>
> >> ---
> >> 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.
I am fine with if statements as long as you just return and do not
bother with else if.
Regards
Marcel
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