Hi Alain, Marcel,
On Wed, Jan 8, 2020 at 12:08 PM Alain Michaud
<alainmichaud@xxxxxxxxxx> wrote:
>
> Hi Luiz,
>
>
> On Wed, Jan 8, 2020 at 3:00 PM Luiz Augusto von Dentz
> <luiz.dentz@xxxxxxxxx> wrote:
> >
> > Hi Alain,
> >
> > On Wed, Jan 8, 2020 at 7:04 AM Alain Michaud
<alainmichaud@xxxxxxxxxx> wrote:
> > >
> > > Hi Luiz,
> > >
> > >
> > > On Tue, Jan 7, 2020 at 6:22 PM Luiz Augusto von Dentz
> > > <luiz.dentz@xxxxxxxxx> wrote:
> > > >
> > > > Hi Alain,
> > > >
> > > > On Mon, Jan 6, 2020 at 5:31 PM Alain Michaud
<alainm@xxxxxxxxxxxx> wrote:
> > > > >
> > > > > This change accomplishes 2 things:
> > > > > 1. Drop device security data from previously paired
devices
> > > > > using blocked keys.
> > > > > 2. Send the list of known bad keys that should be
blocked to the kernel
> > > > > if supported.
> > > > >
> > > > > In particular keys from the Google Titan Security key are
being
> > > > > blocked.
> > > > >
> > > > > For additional background information, please see
> > > > >
https://security.googleblog.com/2019/05/titan-keys-update.html
> > > > > ---
> > > > >
> > > > > src/adapter.c | 140
+++++++++++++++++++++++++++++++++++++++++++++++---
> > > > > 1 file changed, 134 insertions(+), 6 deletions(-)
> > > > >
> > > > > diff --git a/src/adapter.c b/src/adapter.c
> > > > > index cef25616f..9c41ebe86 100644
> > > > > --- a/src/adapter.c
> > > > > +++ b/src/adapter.c
> > > > > @@ -99,10 +99,27 @@
> > > > > #define DISTANCE_VAL_INVALID 0x7FFF
> > > > > #define PATHLOSS_MAX 137
> > > > >
> > > > > +/*
> > > > > + * These are known security keys that have been
compromised.
> > > > > + * If this grows or there are needs to be platform
specific, it is
> > > > > + * conceivable that these could be read from a config
file.
> > > > > + */
> > > > > +static const struct mgmt_blocked_key_info blocked_keys[]
= {
> > > > > + /* Google Titan Security Keys */
> > > > > + { HCI_BLOCKED_KEY_TYPE_LTK,
> > > > > + {0xbf, 0x01, 0xfb, 0x9d, 0x4e, 0xf3,
0xbc, 0x36,
> > > > > + 0xd8, 0x74, 0xf5, 0x39, 0x41, 0x38,
0x68, 0x4c}},
> > > > > + { HCI_BLOCKED_KEY_TYPE_IRK,
> > > > > + {0xa5, 0x99, 0xba, 0xe4, 0xe1, 0x7c,
0xa6, 0x18,
> > > > > + 0x22, 0x8e, 0x07, 0x56, 0xb4, 0xe8,
0x5f, 0x01}},
> > > > > +};
> > > > > +
> > > > > static DBusConnection *dbus_conn = NULL;
> > > > >
> > > > > static bool kernel_conn_control = false;
> > > > >
> > > > > +static bool kernel_blocked_keys_supported = false;
> > > > > +
> > > > > static GList *adapter_list = NULL;
> > > > > static unsigned int adapter_remaining = 0;
> > > > > static bool powering_down = false;
> > > > > @@ -124,6 +141,7 @@ struct link_key_info {
> > > > > unsigned char key[16];
> > > > > uint8_t type;
> > > > > uint8_t pin_len;
> > > > > + bool is_blocked;
> > > > > };
> > > > >
> > > > > struct smp_ltk_info {
> > > > > @@ -135,12 +153,14 @@ struct smp_ltk_info {
> > > > > uint16_t ediv;
> > > > > uint64_t rand;
> > > > > uint8_t val[16];
> > > > > + bool is_blocked;
> > > > > };
> > > > >
> > > > > struct irk_info {
> > > > > bdaddr_t bdaddr;
> > > > > uint8_t bdaddr_type;
> > > > > uint8_t val[16];
> > > > > + bool is_blocked;
> > > > > };
> > > > >
> > > > > struct conn_param {
> > > > > @@ -3439,6 +3459,20 @@ static int str2buf(const char
*str, uint8_t *buf, size_t blen)
> > > > > return 0;
> > > > > }
> > > > >
> > > > > +static bool is_blocked_key(uint8_t key_type, uint8_t
*key_value)
> > > > > +{
> > > > > + uint32_t i = 0;
> > > > > +
> > > > > + for (i = 0; i < ARRAY_SIZE(blocked_keys); ++i) {
> > > > > + if (key_type == blocked_keys[i].type &&
> > > > > +
!memcmp(blocked_keys[i].val, key_value,
> > > > > +
sizeof(blocked_keys[i].val)))
> > > > > + return true;
> > > > > + }
> > > > > +
> > > > > + return false;
> > > > > +}
> > > > > +
> > > > > static struct link_key_info *get_key_info(GKeyFile
*key_file, const char *peer)
> > > > > {
> > > > > struct link_key_info *info = NULL;
> > > > > @@ -3461,6 +3495,9 @@ static struct link_key_info
*get_key_info(GKeyFile *key_file, const char *peer)
> > > > > info->pin_len = g_key_file_get_integer(key_file,
"LinkKey", "PINLength",
> > > > > NULL);
> > > > >
> > > > > + info->is_blocked =
is_blocked_key(HCI_BLOCKED_KEY_TYPE_LINKKEY,
> > > > > +
info->key);
> > > > > +
> > > > > failed:
> > > > > g_free(str);
> > > > >
> > > > > @@ -3534,6 +3571,9 @@ static struct smp_ltk_info
*get_ltk(GKeyFile *key_file, const char *peer,
> > > > > else
> > > > > ltk->master = master;
> > > > >
> > > > > + ltk->is_blocked =
is_blocked_key(HCI_BLOCKED_KEY_TYPE_LTK,
> > > > > +
ltk->val);
> > > > > +
> > > > > failed:
> > > > > g_free(key);
> > > > > g_free(rand);
> > > > > @@ -3584,6 +3624,9 @@ static struct irk_info
*get_irk_info(GKeyFile *key_file, const char *peer,
> > > > > else
> > > > > str2buf(&str[0], irk->val,
sizeof(irk->val));
> > > > >
> > > > > + irk->is_blocked =
is_blocked_key(HCI_BLOCKED_KEY_TYPE_LINKKEY,
> > > > > +
irk->val);
> > > > > +
> > > > > failed:
> > > > > g_free(str);
> > > > >
> > > > > @@ -4142,21 +4185,55 @@ static void load_devices(struct
btd_adapter *adapter)
> > > > > g_key_file_load_from_file(key_file,
filename, 0, NULL);
> > > > >
> > > > > key_info = get_key_info(key_file,
entry->d_name);
> > > > > - if (key_info)
> > > > > - keys = g_slist_append(keys,
key_info);
> > > > >
> > > > > bdaddr_type = get_le_addr_type(key_file);
> > > > >
> > > > > ltk_info = get_ltk_info(key_file,
entry->d_name, bdaddr_type);
> > > > > - if (ltk_info)
> > > > > - ltks = g_slist_append(ltks,
ltk_info);
> > > > >
> > > > > slave_ltk_info =
get_slave_ltk_info(key_file, entry->d_name,
> > > > >
bdaddr_type);
> > > > > +
> > > > > + irk_info = get_irk_info(key_file,
entry->d_name, bdaddr_type);
> > > > > +
> > > > > + // If any key for the device is blocked,
we discard all.
> > > > > + if ((key_info && key_info->is_blocked) ||
> > > > > + (ltk_info &&
ltk_info->is_blocked) ||
> > > > > + (slave_ltk_info &&
> > > > > +
slave_ltk_info->is_blocked) ||
> > > > > + (irk_info &&
irk_info->is_blocked)) {
> > > >
> > > > Perhaps it would be more efficient if we don't add
is_blocked as a
> > > > member of these keys and instead pass bool variable to
get_*_info
> > > > which just set it in case the key is blocked, that way if
is_blocked
> > > > is set for get_key_info you don't have to free anything.
Also it might
> > > > be a good idea to move the handling of loading the keys to
another
> > > > function i.e. load_keys to make it simpler to bail out,
etc. Have you
> > > > though about the possibility of just using a the device
block API when
> > > > you detect it is using compromised keys? That way the
application can
> > > > detect the device is in fact blocked and can either remove
the device,
> > > > which would clean up the storage as well (see my comments
bellow), or
> > > > unblock it in order to continue using the device.
> > >
> > > My thoughts was to keep the contract simple. if the return
is not
> > > null then a key exists, it can be blocked or not blocked. It
feels a
> > > bit weird to have a contract return null but a parameter
tells you
> > > that it's been blocked. The extra allocation/free doesn't
seem like a
> > > lot of overhead for what is expected to be a rare case
(blocked keys).
> >
> > Fair enough, I suggested that because the is_block logic seems
to
> > apply to all of the keys not just the key that was compromised,
anyway
> > Im probably getting a little too paranoid regarding overhead
but I
> > don't think we had loose anything by avoiding the extra
> > allocation/free
> Correct. The idea is that if any of the keys from the device is
> blocked, the device
> is simply ignored.
>
> >
> > > >
> > > > > + if (key_info) {
> > > > > + g_free(key_info);
> > > > > + key_info = NULL;
> > > > > + }
> > > > > +
> > > > > + if (ltk_info) {
> > > > > + g_free(ltk_info);
> > > > > + ltk_info = NULL;
> > > > > + }
> > > > > +
> > > > > + if (slave_ltk_info) {
> > > > > + g_free(slave_ltk_info);
> > > > > + slave_ltk_info = NULL;
> > > > > + }
> > > > > +
> > > > > + if (irk_info) {
> > > > > + g_free(irk_info);
> > > > > + irk_info = NULL;
> > > > > + }
> > > > > +
> > > > > + goto free;
> > > > > + }
> > > > > +
> > > > > + if (key_info)
> > > > > + keys = g_slist_append(keys,
key_info);
> > > > > +
> > > > > + if (ltk_info)
> > > > > + ltks = g_slist_append(ltks,
ltk_info);
> > > > > +
> > > >
> > > > Perhaps I missing something but don't we need to clear
these keys form
> > > > the storage once we figure they are blocked or there is any
reason to
> > > > leave them in there so we can unblock?
> > > Since these are expected to be rare cases, I didn't go
through the
> > > extent to clear them from storage. Having them in storage
also can
> > > help with diagnosability.
> >
> > That is an interesting point, but we don't allow new pairing
with
> > compromised keys with these changes or do we? If we want to
allow
> > diagnosing in all cases we could actually store the blocked
flag into
> > the storage so something like a diagnostic tool can fetch the
> > information directly.
> With these changes, the device is simply dropped from the list
> entirely. The user is free to attempt to pair it again. If the
> device is fixed, pairing will work and the key will be
overwritten, if
> the device is still broken, the pairing will fail and the user
will
> see the error. Given that for now, the keys are hardcoded and a
> relatively small list, it feels like overkill to store an
additional
> flag for it. This may be something we'd want to do if the list of
> blocked keys grows beyond something that is easily manageable. If
> that is the case, I also think we should read the blocked keys
from a
> configuration file rather than hardcoded in the code as it
currently
> is.
All good, just waiting the kernel changes to be applied then we can
go
ahead with these changes as well, @Marcel are you planning to merge
the kernel changes?
> >
> > > >
> > > > > if (slave_ltk_info)
> > > > > ltks = g_slist_append(ltks,
slave_ltk_info);
> > > > >
> > > > > - irk_info = get_irk_info(key_file,
entry->d_name, bdaddr_type);
> > > > > if (irk_info)
> > > > > irks = g_slist_append(irks,
irk_info);
> > > > >
> > > > > @@ -8568,6 +8645,42 @@ static bool set_static_addr(struct
btd_adapter *adapter)
> > > > > return false;
> > > > > }
> > > > >
> > > > > +static void set_blocked_keys_complete(uint8_t status,
uint16_t length,
> > > > > + const void
*param, void *user_data)
> > > > > +{
> > > > > + struct btd_adapter *adapter = user_data;
> > > > > +
> > > > > + if (status != MGMT_STATUS_SUCCESS) {
> > > > > + btd_error(adapter->dev_id,
> > > > > + "Failed to set blocked
keys: %s (0x%02x)",
> > > > > + mgmt_errstr(status),
status);
> > > > > + return;
> > > > > + }
> > > > > +
> > > > > + DBG("Successfully set blocked keys for index %u",
adapter->dev_id);
> > > > > +}
> > > > > +
> > > > > +static bool set_blocked_keys(struct btd_adapter *adapter)
> > > > > +{
> > > > > + uint8_t buffer[sizeof(struct
mgmt_cp_set_blocked_keys) +
> > > > > +
sizeof(blocked_keys)] = { 0 };
> > > > > + struct mgmt_cp_set_blocked_keys *cp =
> > > > > + (struct
mgmt_cp_set_blocked_keys *)buffer;
> > > > > + int i;
> > > > > +
> > > > > + cp->key_count = ARRAY_SIZE(blocked_keys);
> > > > > + for (i = 0; i < cp->key_count; ++i) {
> > > > > + cp->keys[i].type = blocked_keys[i].type;
> > > > > + memcpy(cp->keys[i].val,
blocked_keys[i].val,
> > > > > +
sizeof(cp->keys[i].val));
> > > > > + }
> > > > > +
> > > > > + return mgmt_send(mgmt_master,
MGMT_OP_SET_BLOCKED_KEYS, adapter->dev_id,
> > > > > +
sizeof(buffer), buffer,
> > > > > +
set_blocked_keys_complete,
> > > > > + adapter,
NULL);
> > > > > +}
> > > > > +
> > > > > static void read_info_complete(uint8_t status, uint16_t
length,
> > > > > const void
*param, void *user_data)
> > > > > {
> > > > > @@ -8795,6 +8908,13 @@ static void
read_info_complete(uint8_t status, uint16_t length,
> > > > >
> > > > > set_name(adapter, btd_adapter_get_name(adapter));
> > > > >
> > > > > + if (kernel_blocked_keys_supported &&
!set_blocked_keys(adapter)) {
> > > > > + btd_error(adapter->dev_id,
> > > > > + "Failed to set blocked
keys for index %u",
> > > > > + adapter->dev_id);
> > > > > + goto failed;
> > > > > + }
> > > > > +
> > > > > if (main_opts.pairable &&
> > > > > !(adapter->current_settings &
MGMT_SETTING_BONDABLE))
> > > > > set_mode(adapter, MGMT_OP_SET_BONDABLE,
0x01);
> > > > > @@ -8972,9 +9092,17 @@ static void
read_commands_complete(uint8_t status, uint16_t length,
> > > > > for (i = 0; i < num_commands; i++) {
> > > > > uint16_t op = get_le16(rp->opcodes + i);
> > > > >
> > > > > - if (op == MGMT_OP_ADD_DEVICE) {
> > > > > + switch (op) {
> > > > > + case MGMT_OP_ADD_DEVICE:
> > > > > DBG("enabling kernel-side
connection control");
> > > > > kernel_conn_control = true;
> > > > > + break;
> > > > > + case MGMT_OP_SET_BLOCKED_KEYS:
> > > > > + DBG("kernel supports the
set_blocked_keys op");
> > > > > + kernel_blocked_keys_supported =
true;
> > > > > + break;
> > > > > + default:
> > > > > + break;
> > > > > }
> > > > > }
> > > > > }
> > > > > --
> > > > > 2.24.1.735.g03f4e72817-goog
> > > > >
> > > >
> > > >
> > > > --
> > > > Luiz Augusto von Dentz
> >
> >
> >
> > --
> > Luiz Augusto von Dentz
