2020-02-18 11:06:28

by Yun-hao Chung

Subject: [Bluez PATCH v1] bluetooth: fix passkey uninitialized when used

From: "[email protected]" <[email protected]>

This issue cause a warning here
https://groups.google.com/forum/#!topic/clang-built-linux/kyRKCjRsGoU

Signed-off-by: Howard Chung <[email protected]>
---

net/bluetooth/smp.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index 50e0ac692ec4..fa40de69e487 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -2179,10 +2179,12 @@ static u8 smp_cmd_pairing_random(struct l2cap_conn *conn, struct sk_buff *skb)
*/
if (hci_find_ltk(hcon->hdev, &hcon->dst, hcon->dst_type,
hcon->role)) {
+ /* Set passkey to 0. The value can be any number since
+ * it'll be ignored anyway.
+ */
err = mgmt_user_confirm_request(hcon->hdev, &hcon->dst,
hcon->type,
- hcon->dst_type,
- passkey, 1);
+ hcon->dst_type, 0, 1);
if (err)
return SMP_UNSPECIFIED;
set_bit(SMP_FLAG_WAIT_USER, &smp->flags);
--
2.25.0.265.gbab2e86ba0-goog

2020-02-18 21:20:59

by Marcel Holtmann

Subject: Re: [Bluez PATCH v1] bluetooth: fix passkey uninitialized when used

Hi Howard,

> From: "[email protected]" <[email protected]>

any chance you fix your git setting to provide a From: with full name and email like you have in the signed-off-by line.

>
> This issue cause a warning here
> https://groups.google.com/forum/#!topic/clang-built-linux/kyRKCjRsGoU
>
> Signed-off-by: Howard Chung <[email protected]>
> ---
>
> net/bluetooth/smp.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
> index 50e0ac692ec4..fa40de69e487 100644
> --- a/net/bluetooth/smp.c
> +++ b/net/bluetooth/smp.c
> @@ -2179,10 +2179,12 @@ static u8 smp_cmd_pairing_random(struct l2cap_conn *conn, struct sk_buff *skb)
> */
> if (hci_find_ltk(hcon->hdev, &hcon->dst, hcon->dst_type,
> hcon->role)) {
> + /* Set passkey to 0. The value can be any number since
> + * it'll be ignored anyway.
> + */
> err = mgmt_user_confirm_request(hcon->hdev, &hcon->dst,
> hcon->type,
> - hcon->dst_type,
> - passkey, 1);
> + hcon->dst_type, 0, 1);
> if (err)
> return SMP_UNSPECIFIED;
> set_bit(SMP_FLAG_WAIT_USER, &smp->flags);

Since I have to look at this again, I wonder if we do this correctly. Either we have a bug there or not enough comments on why the code is correct.

if (hcon->out) {
u8 cfm[16];

err = smp_f4(smp->tfm_cmac, smp->remote_pk, smp->local_pk,
smp->rrnd, 0, cfm);
if (err)
return SMP_UNSPECIFIED;

if (crypto_memneq(smp->pcnf, cfm, 16))
return SMP_CONFIRM_FAILED;
} else {
smp_send_cmd(conn, SMP_CMD_PAIRING_RANDOM, sizeof(smp->prnd),
smp->prnd);
SMP_ALLOW_CMD(smp, SMP_CMD_DHKEY_CHECK);

/* Only Just-Works pairing requires extra checks */
if (smp->method != JUST_WORKS)
goto mackey_and_ltk;

/* If there already exists long term key in local host, leave
* the decision to user space since the remote device could
* be legitimate or malicious.
*/
if (hci_find_ltk(hcon->hdev, &hcon->dst, hcon->dst_type,
hcon->role)) {
err = mgmt_user_confirm_request(hcon->hdev, &hcon->dst,
hcon->type,
hcon->dst_type,
passkey, 1);
if (err)
return SMP_UNSPECIFIED;
set_bit(SMP_FLAG_WAIT_USER, &smp->flags);
}
}

mackey_and_ltk:
/* Generate MacKey and LTK */
err = sc_mackey_and_ltk(smp, smp->mackey, smp->tk);
if (err)
return SMP_UNSPECIFIED;

if (smp->method == JUST_WORKS || smp->method == REQ_OOB) {
if (hcon->out) {
sc_dhkey_check(smp);
SMP_ALLOW_CMD(smp, SMP_CMD_DHKEY_CHECK);
}
return 0;
}

err = smp_g2(smp->tfm_cmac, pkax, pkbx, na, nb, &passkey);
if (err)
return SMP_UNSPECIFIED;

err = mgmt_user_confirm_request(hcon->hdev, &hcon->dst, hcon->type,
hcon->dst_type, passkey, 0);
if (err)
return SMP_UNSPECIFIED;

set_bit(SMP_FLAG_WAIT_USER, &smp->flags);

return 0;
}

Since we are already !hcon->out and smp->method == JUST_WORKS, why are we moving into mackey_and_ltk path? If we have already an LTK, then we just should bail out after setting SMP_FLAG_WAIT_USER, right?

@@ -2115,7 +2115,7 @@ static u8 smp_cmd_pairing_random(struct l2cap_conn *conn, struct sk_buff *skb)
struct l2cap_chan *chan = conn->smp;
struct smp_chan *smp = chan->data;
struct hci_conn *hcon = conn->hcon;
- u8 *pkax, *pkbx, *na, *nb;
+ u8 *pkax, *pkbx, *na, *nb, confirm_hint;
u32 passkey;
int err;

@@ -2179,13 +2179,9 @@ static u8 smp_cmd_pairing_random(struct l2cap_conn *conn, struct sk_buff *skb)
*/
if (hci_find_ltk(hcon->hdev, &hcon->dst, hcon->dst_type,
hcon->role)) {
- err = mgmt_user_confirm_request(hcon->hdev, &hcon->dst,
- hcon->type,
- hcon->dst_type,
- passkey, 1);
- if (err)
- return SMP_UNSPECIFIED;
- set_bit(SMP_FLAG_WAIT_USER, &smp->flags);
+ passkey = 0;
+ confirm_hint = 1;
+ goto confirm;
}
}

@@ -2207,8 +2203,11 @@ static u8 smp_cmd_pairing_random(struct l2cap_conn *conn, struct sk_buff *skb)
if (err)
return SMP_UNSPECIFIED;

+ confirm_hint = 0;
+
+confirm:
err = mgmt_user_confirm_request(hcon->hdev, &hcon->dst, hcon->type,
- hcon->dst_type, passkey, 0);
+ hcon->dst_type, passkey, confirm_hint);
if (err)
return SMP_UNSPECIFIED;

So isn’t this the better approach and actually cleaner code? And I would still add a comment above setting passkey = 0.

Am I missing anything?

Regards

Marcel