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Avoid unnecessary delegated role downloads #811

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Merged
merged 2 commits into from
Dec 31, 2018
Merged

Avoid unnecessary delegated role downloads #811

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42689d2
DOC: loudly mark deprecations of all_targets and targets_of_role
awwad Dec 7, 2018
3b4e0e6
Fix unnecessary delegated role downloads w/ targets_of_role
awwad Dec 7, 2018
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32 changes: 31 additions & 1 deletion tuf/client/updater.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2349,6 +2349,12 @@ def _ensure_not_expired(self, metadata_object, metadata_rolename):
def all_targets(self):
"""
<Purpose>

NOTE: This function is deprecated. Its behavior with regard to which
delegating Targets roles are trusted to determine how to validate a
delegated Targets role is NOT WELL DEFINED. Please transition to use of
get_one_valid_targetinfo()!

Get a list of the target information for all the trusted targets on the
repository. This list also includes all the targets of delegated roles.
Targets of the list returned are ordered according the trusted order of
Expand Down Expand Up @@ -2558,6 +2564,12 @@ def _targets_of_role(self, rolename, targets=None, skip_refresh=False):
def targets_of_role(self, rolename='targets'):
"""
<Purpose>

NOTE: This function is deprecated. Use with rolename 'targets' is secure
and the behavior well-defined, but use with any delegated targets role is
not. Please transition use for delegated targets roles to
get_one_valid_targetinfo(). More information is below.

Return a list of trusted targets directly specified by 'rolename'.
The returned information is a list conformant to
'tuf.formats.TARGETINFOS_SCHEMA', and has the form:
Expand Down Expand Up @@ -2603,7 +2615,25 @@ def targets_of_role(self, rolename='targets'):
# Raise 'securesystemslib.exceptions.FormatError' if there is a mismatch.
securesystemslib.formats.RELPATH_SCHEMA.check_match(rolename)

self._refresh_targets_metadata(refresh_all_delegated_roles=True)
# If we've been given a delegated targets role, we don't know how to
# validate it without knowing what the delegating role is -- there could
# be several roles that delegate to the given role. Behavior of this
# function for roles other than Targets is not well defined as a result.
# This function is deprecated, but:
# - Usage of this function or a future successor makes sense when the
# role of interest is Targets, since we always know exactly how to
# validate Targets (We use root.).
# - Until it's removed (hopefully soon), we'll try to provide what it has
# always provided. To do this, we fetch and "validate" all delegated
# roles listed by snapshot. For delegated roles only, the order of the
# validation impacts the security of the validation -- the most-
# recently-validated role delegating to a role you are currently
# validating determines the expected keyids and threshold of the role
# you are currently validating. That is NOT GOOD. Again, please switch
# to get_one_valid_targetinfo, which is well-defined and secure.
if rolename != 'targets':
self._refresh_targets_metadata(refresh_all_delegated_roles=True)


if not tuf.roledb.role_exists(rolename, self.repository_name):
raise tuf.exceptions.UnknownRoleError(rolename)
Expand Down