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In-Reply-To: <1579209808.12244.3@gmail.com>
From:   Alain Michaud <alainmichaud@google.com>
Date:   Thu, 16 Jan 2020 13:42:50 -0800
Message-ID: <CALWDO_XVYi1wMKEJuJ3RjszWErYznFSwhoMK4Ui0W6JFJo0hXg@mail.gmail.com>
Subject: Re: [PATCH v5 3/3] Loading keys that should be blocked by the kernel.
To:     Luiz Von Dentz <luiz.dentz@gmail.com>
Cc:     Alain Michaud <alainm@chromium.org>,
        BlueZ <linux-bluetooth@vger.kernel.org>,
        Marcel Holtmann <marcel@holtmann.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-bluetooth-owner@vger.kernel.org
Precedence: bulk

Thanks Luiz!


On Thu, Jan 16, 2020 at 1:23 PM Luiz Von Dentz <luiz.dentz@gmail.com> wrote:
>
> Hi Alain,
>
> On Thu, Jan 16, 2020 at 8:18 AM, Alain Michaud
> <alainmichaud@google.com> 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@gmail.com> wrote:
> >>
> >>  Hi Alain, Marcel,
> >>
> >>  On Wed, Jan 8, 2020 at 12:08 PM Alain Michaud
> >> <alainmichaud@google.com> wrote:
> >>  >
> >>  > Hi Luiz,
> >>  >
> >>  >
> >>  > On Wed, Jan 8, 2020 at 3:00 PM Luiz Augusto von Dentz
> >>  > <luiz.dentz@gmail.com> wrote:
> >>  > >
> >>  > > Hi Alain,
> >>  > >
> >>  > > On Wed, Jan 8, 2020 at 7:04 AM Alain Michaud
> >> <alainmichaud@google.com> wrote:
> >>  > > >
> >>  > > > Hi Luiz,
> >>  > > >
> >>  > > >
> >>  > > > On Tue, Jan 7, 2020 at 6:22 PM Luiz Augusto von Dentz
> >>  > > > <luiz.dentz@gmail.com> wrote:
> >>  > > > >
> >>  > > > > Hi Alain,
> >>  > > > >
> >>  > > > > On Mon, Jan 6, 2020 at 5:31 PM Alain Michaud
> >> <alainm@chromium.org> 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
>
>