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Bluetooth: SMP: Add option to disallow unauthenticated re-pairing

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Disallows all unauthenticated pairing attempts made by the
peer where an unauthenticated bond already exists.
This would enable cases where an attacker could copy the peer device
address to connect and start an unauthenticated pairing procedure
to replace the existing bond. Now in order to create a new bond the old
bond has to be explicitly deleted with bt_unpair.

Added option to disable this rule in order to maintain backwards
compatibility in case this behavior is accepted.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>
This commit is contained in:
Joakim Andersson 2019-11-07 16:15:50 +01:00 • committed by Johan Hedberg
commit 64d6d1079c
2 changed files with 17 additions and 0 deletions
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11
subsys/bluetooth/host/Kconfig
View file

@ -298,6 +298,17 @@ config BT_SMP_SC_ONLY
Security Mode 1 Level 4 stands for authenticated LE Secure Connections Security Mode 1 Level 4 stands for authenticated LE Secure Connections
pairing with encryption. Enabling this option disables legacy pairing. pairing with encryption. Enabling this option disables legacy pairing.
config BT_SMP_ALLOW_UNAUTH_OVERWRITE
bool "Allow unauthenticated pairing for paired device"
help
This option allows all unauthenticated pairing attempts made by the
peer where an unauthenticated bond already exists.
This would enable cases where an attacker could copy the peer device
address to connect and start an unauthenticated pairing procedure
to replace the existing bond. When this option is disabled in order
to create a new bond the old bond has to be explicitly deleted with
bt_unpair.
config BT_FIXED_PASSKEY config BT_FIXED_PASSKEY
bool "Use a fixed passkey for pairing" bool "Use a fixed passkey for pairing"
help help

6
subsys/bluetooth/host/smp.c
View file

@ -684,6 +684,12 @@ static bool update_keys_check(struct bt_smp *smp)
return false; return false;
} }
if (!IS_ENABLED(CONFIG_BT_SMP_ALLOW_UNAUTH_OVERWRITE) &&
(!(conn->le.keys->flags & BT_KEYS_AUTHENTICATED)
&& smp->method == JUST_WORKS)) {
return false;
}
return true; return true;
} }