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Do not panic if not root #80

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pfactum opened this issue Oct 13, 2022 · 1 comment
Open

Do not panic if not root #80

pfactum opened this issue Oct 13, 2022 · 1 comment

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@pfactum
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pfactum commented Oct 13, 2022

Hello.

Given the systemd (or a similar system manager) is available, it should be possible to run iodined with very restricted privileges and on behalf of a non-root user (even a dynamically generated one), granting additional capabilities via AmbientCapabilities=. Hence, unconditional panic in check_superuser() should be avoided. So, instead of calling check_superuser(), at least on Linux, there should be a check against required capability (there's libcap-ng for this). For creating a tun device it'd be CAP_NET_ADMIN, for binding on port 53 it's CAP_NET_BIND_SERVICE, for changing the user it is CAP_SETUID and CAP_SETGID.

Thanks.
pfactum added a commit to pfactum/iodine that referenced this issue Oct 17, 2022
@pfactum
check capabilities, not effective user ID
c25eed6 
Under Linux, a process may not be run under root, yet it may have a permission
to do what a superuser may do given specific capabilities are granted.

This commit makes iodine not depend on EUID being 0 in order to run
properly. Instead, in presence of libcap-ng, the following capabilities
are being checked:

* `CAP_NET_BIND_SERVICES` for server to bind to a port, lower than
  `/proc/sys/net/ipv4/ip_unprivileged_port_start`
* `CAP_NET_ADMIN` to operate on a TUN device
* `CAP_SETUID` and `CAP_SETGID` in case server is configured to change
  the user it runs on behalf of

This change is handy if iodine is being run under a non-root user, provided
`AmbientCapabilities=` and `CapabilityBoundingSet=` of systemd are employed
in the first place.

Fixes: yarrick#80
Signed-off-by: Oleksandr Natalenko <[email protected]>
@pfactum pfactum mentioned this issue Oct 17, 2022
Open
pfactum added a commit to pfactum/iodine that referenced this issue Nov 2, 2022
@pfactum
check capabilities, not effective user ID
ebf4e7e 
Under Linux, a process may not be run under root, yet it may have a permission
to do what a superuser may do given specific capabilities are granted.

This commit makes iodine not depend on EUID being 0 in order to run
properly. Instead, in presence of libcap-ng, the following capabilities
are being checked:

* `CAP_NET_BIND_SERVICES` for server to bind to a port, lower than
  `/proc/sys/net/ipv4/ip_unprivileged_port_start`
* `CAP_NET_ADMIN` to operate on a TUN device
* `CAP_SETUID` and `CAP_SETGID` in case server is configured to change
  the user it runs on behalf of

This change is handy if iodine is being run under a non-root user, provided
`AmbientCapabilities=` and `CapabilityBoundingSet=` of systemd are employed
in the first place.

Fixes: yarrick#80
Signed-off-by: Oleksandr Natalenko <[email protected]>
@osevan
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osevan commented Dec 17, 2023 •
edited
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Could someone merge this?

We need this functionality too.

I want running iodine inside high security container with apparmor protections

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@pfactum @osevan