mirror of
https://github.com/vlang/v.git
synced 2023-08-10 21:13:21 +03:00
62 lines
1.5 KiB
Markdown
62 lines
1.5 KiB
Markdown
## Description:
|
|
|
|
`os` provides common OS/platform independent functions for accessing
|
|
command line arguments, reading/writing files, listing folders,
|
|
handling processes etc.
|
|
|
|
* * *
|
|
|
|
|
|
### Security advice related to TOCTOU attacks
|
|
|
|
A few `os` module functions can lead to the <b>TOCTOU</b> vulnerability if used incorrectly.
|
|
<b>TOCTOU</b> (Time-of-Check-to-Time-of-Use problem) can occur when a file, folder or similar
|
|
is checked for certain specifications (e.g. read, write permissions) and a change is made
|
|
afterwards.
|
|
In the time between the initial check and the edit, an attacker can then cause damage.
|
|
The following example shows an attack strategy on the left and an improved variant on the right
|
|
so that <b>TOCTOU</b> is no longer possible.
|
|
|
|
|
|
<b>Example</b>
|
|
<i>Hint</i>: `os.create()` opens a file in write-only mode
|
|
|
|
<table>
|
|
<tr>
|
|
<td>
|
|
Possibility for TOCTOU attack
|
|
|
|
```v ignore
|
|
if os.is_writable("file"){
|
|
|
|
// >> time to make a quick attack (e.g. symlink /etc/passwd to >file<) <<
|
|
|
|
mut f := os.create('path/to/file') ?
|
|
// <do something with file>
|
|
f.close()
|
|
}
|
|
```
|
|
</td>
|
|
<td>TOCTOU not possible
|
|
|
|
```v ignore
|
|
mut f := os.create('path/to/file') or {
|
|
println("file not writable")
|
|
}
|
|
|
|
// >> do something with file; file is locked <<
|
|
|
|
f.close()
|
|
```
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
<b> Proven affected functions </b></br>
|
|
The following functions should be used with care and only when used correctly.
|
|
|
|
* os.is_readable()
|
|
* os.is_writable()
|
|
* os.is_executable()
|
|
* os.is_link()
|