Re: [PATCH v5 3/3] Loading keys that should be blocked by the kernel.

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Hi Alain,

On Thu, Jan 16, 2020 at 8:18 AM, Alain Michaud <alainmichaud@xxxxxxxxxx> wrote:
Looks like Marcel committed the kernel changes, are we good to commit these?

Thanks!
Alain

On Fri, Jan 10, 2020 at 4:08 PM Luiz Augusto von Dentz
<luiz.dentz@xxxxxxxxx> wrote:

 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




Applied, thanks.

Note that I changed a little bit the commit messages since it was causing some warnings with gitlint:

gitlint: checking commit message...
1: T3 Title has trailing punctuation (.): "MGMT_OP_SET_BLOCKED_KEYS Api definitions."
-----------------------------------------------
gitlint: \033[31mYour commit message contains the above violations.\033[0m Continue with commit anyways (this keeps the current commit message)? [y(es)/n(no)/e(dit)] y
Applying: MGMT_OP_SET_BLOCKED_KEYS Api definitions.
gitlint: checking commit message...
1: T3 Title has trailing punctuation (.): "Adding a shared ARRAY_SIZE macro."
-----------------------------------------------
gitlint: \033[31mYour commit message contains the above violations.\033[0m Continue with commit anyways (this keeps the current commit message)? [y(es)/n(no)/e(dit)] y
Applying: Adding a shared ARRAY_SIZE macro.
gitlint: checking commit message...
1: T3 Title has trailing punctuation (.): "Loading keys that should be blocked by the kernel."
-----------------------------------------------
gitlint: \033[31mYour commit message contains the above violations.\033[0m Continue with commit anyways (this keeps the current commit message)? [y(es)/n(no)/e(dit)] y
Applying: Loading keys that should be blocked by the kernel.



 --
 Luiz Augusto von Dentz





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