Philip Withnall ed81cbc9b5 gdbusauthmechanismsha1: Fix race in keyring_acquire_lock()
There was a time-of-check-to-time-of-use (TOCTTOU) race in the keyring
lock code, where it would check the existence of the lock file using
`access()`, then proceed to call `open(O_CREAT | O_EXCL)` to try and
create the lock file once `access()` showed that it didn’t exist.

The problem is that, because this is happening in a shared directory
(`~/.dbus-keyrings`), another process could quite legitimately create
the lock file in the meantime.

Instead, unconditionally call `open()` and ignore errors from it (which
will be returned if the lock file already exists) until it succeeds (or
the code times out).

This eliminates the TOCTTOU race, and simplifies the timeout behaviour
so there aren’t two loops (check for existence, try to create)
happening. It brings this code in line with what dbus.git does (see
`_dbus_keyring_lock()`).

Signed-off-by: Philip Withnall <withnall@endlessm.com>

Fixes: #1954
2020-05-05 16:07:32 +01:00
..
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