Previously, Service Workers could spawn in a process that isn't subscribed
to permission updates, which could happen if that process hadn't loaded any
same-origin documents. To address this, parent-process logic for spawning
Service Workers would snapshot the permissions state to be sent to a content
process.
Unfortunately, this approach could lead to outdated, unsynchronized permissions.
Note that nsIPermissionManager::SetPermissionsWithKey is only used to initialize
permissions for a given key and is a no-op if already called with the same key
in a given process. As a result, the following sequence of events could happen:
Assume a content process CP that isn't subscribed to permission changes for an
origin A:
1) Parent process decides to spawn an origin A Service Worker in CP,
snapshotting a value V for permission P.
2) The Service Worker is spawned in CP, setting CP's permission manager's
permission P to value V (for origin A).
3) Parent process updates its permission P to a value A', which is not
broadcasted to CP (because it's not subscribed).
4) By now, the initial Service Worker has been terminated, and the parent
process decides once again to spawn an origin A Service Worker in CP.
5) The Service Worker is spawned in CP, but the call to SetPermissionsWithKey
is a no-op, leaving CP1 with a mismatched value for permission P.
An additional scenario is if the parent process updates a permission during a
remote Service Worker's lifetime.
This patch, which would subscribe CP1 to permission updates when the parent
process knows a Service Worker would be spawned in CP1, prevents these problems.
Differential Revision: https://phabricator.services.mozilla.com/D48620
--HG--
extra : moz-landing-system : lando
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