linux-kernel - Re: [PATCH] proc: Don't allow empty /proc/PID/cmdline for user tasks

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Message-ID: <20180517185033.GA24408@avx2>
Date:   Thu, 17 May 2018 21:50:33 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     tj@...nel.org
Cc:     linux-kernel@...r.kernel.org
Subject: Re: [PATCH] proc: Don't allow empty /proc/PID/cmdline for user tasks

> Kernel threads have empty /proc/PID/cmdline and some userland tools
> including ps(1) and older versions of systemd use this to detect
> kernel threads.

Those tools are broken. Systemd is fixed, see
https://github.com/systemd/systemd/blob/master/src/basic/process-util.c#L442

Empty /proc/*/cmdline is perfectly fine as long as

	execve(filename, NULL, NULL)

is fine.

> However, any userland program can emulate the
> behavior by making its argvs unavailable and trick the affected tools
> into thinking that the task is a kernel thread.

Or it can set ->comm to "[kthreadd] and cmdline to "[kthreadd]".