[FS#988] Procd does not respect a user's groups when using parameter user

[LEDE Bugs]

The following task has a new comment added:

FS#988 - Procd does not respect a user's groups when using parameter user
User who did this - Alexander Lochmann (flipreverse)

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Where do I find that file instance.c?
I do not have such file in my checkout (https://git.lede-project.org/source.git).
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More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=988#comment4307