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68 lines
3.1 KiB
Markdown
68 lines
3.1 KiB
Markdown
# Osquery: Consider joining against the users table
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## Proper use of JOIN to return osquery data for users
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Many an osquery user has encountered a situation like the following:
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```
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$ osqueryi
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Using a virtual database. Need help, type '.help'
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osquery> SELECT uid, name FROM chrome_extensions LIMIT 3;
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+-----+--------------------------------------------+
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| uid | name |
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+-----+--------------------------------------------+
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| 501 | Slides |
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| 501 | Docs |
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| 501 | 1Password extension (desktop app required) |
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+-----+--------------------------------------------+
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osquery>
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$ sudo osqueryi
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Using a virtual database. Need help, type '.help'
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osquery> SELECT uid, name FROM chrome_extensions LIMIT 3;
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W0519 09:35:27.624747 415233472 virtual_table.cpp:959] The chrome_extensions table returns data based on the current user by default, consider JOINing against the users table
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W0519 09:35:27.625207 415233472 virtual_table.cpp:974] Please see the table documentation: https://osquery.io/schema/#chrome_extensions
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```
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Our query runs as expected when `osqueryi` is run as a normal user, but returns a warning message and no results when run as root via `sudo osqueryi`.
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This same issue manifests on many tables that include a `uid` column:
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- `authorized_keys`
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- `chrome_extension_content_scripts`
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- `chrome_extensions`
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- `crashes`
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- `docker_container_processes`
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- `firefox_addons`
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- `known_hosts`
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- `opera_extensions`
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- `safari_extensions`
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- `shell_history`
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- `user_ssh_keys`
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### What’s going on here?
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As stated in the error message, these tables return “data based on the current user by default”. When run as a normal user, the implementations know to look in paths relative to the user’s home directories. A query running as root does not know which directories to check.
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### The solution
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Show osquery which users to retrieve the data for. Typically this is achieved by a `JOIN` against the `users` table to retrieve data for every user on the system:
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```
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SELECT uid, name
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FROM users CROSS JOIN chrome_extensions USING (uid)
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```
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Writing the query with this `JOIN` ensures that osquery first generates the list of users, and then provides the user `uid`s to the `chrome_extensions` table when generating that data.
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Note: It is important to use `CROSS JOIN` as this tells the query optimizer not to reorder the evaluation of the tables. If we use a regular `JOIN` it is possible that reordering could result in the original error being encountered (because the `chrome_extensions` table generates with no `uid` in its context).
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<meta name="category" value="guides">
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<meta name="authorGitHubUsername" value="zwass">
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<meta name="authorFullName" value="Zach Wasserman">
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<meta name="publishedOn" value="2021-05-06">
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<meta name="articleTitle" value="Osquery: Consider joining against the users table">
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<meta name="articleImageUrl" value="../website/assets/images/articles/osquery-consider-joining-against-the-users-table-cover-700x437@2x.jpeg">
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