qmi-proxy running as non-root user

[Ben Chan]

Hi Aleksander,

qmi-proxy is currently expected to run as root. IIUC, that's enforced by
incoming_cb and qmi_proxy_new in qmi-proxy.c. I guess it's a security
measure to prevent any arbitrary client application to access the QMI port
via qmi-proxy, unless it has root privilege.

The implication of this approach is that both qmi-proxy and ModemManager
need to run as root, which may not be ideal in some scenarios. For example,
I'm trying to run ModemManager in a sandboxed environment (i.e. non-root,
with limited access to only tty/usb devices, e.g. /dev/cdc-wdm0, associated
with modems).

I'm wondering if libqmi can provide a build time option to disable the root
privilege check in qmi-proxy. Alternatively, qmi-proxy can simply rely on
the file permissions to control the access to /dev/cdc-wdm*, and accept a
client process that can access /dev/cdc-wdm*. The rationale is that if a
client process can access /dev/cdc-wdm*, it can just bypass qmi-proxy.

How do you think?

Thanks,
Ben
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