On Fri, May 24, 2024 at 05:30:03PM +0800, Mikhail Ivanov wrote:
> Hello! This is v2 RFC patch dedicated to socket protocols restriction.
>
> It is based on the landlock's mic-next branch on top of v6.9 kernel
> version.
Hello Mikhail!
I patched in your patchset and tried to use the feature with a small
demo tool, but I ran into what I think is a bug -- do you happen to
know what this might be?
I used 6.10-rc1 as a base and patched your patches on top.
The code is a small tool called "nonet", which does the following:
- Disable socket creation with a Landlock ruleset with the following
attributes:
struct landlock_ruleset_attr attr = {
.handled_access_socket = LANDLOCK_ACCESS_SOCKET_CREATE,
};
- open("/dev/null", O_WRONLY)
Expected result:
- open() should work
Observed result:
- open() fails with EACCES.
I traced this with perf, and found that the open() gets rejected from
Landlock's hook_file_open, whereas hook_socket_create does not get
invoked. This is surprising to me -- Enabling a policy for socket
creation should not influence the outcome of opening files!
Tracing commands:
sudo perf probe hook_socket_create '$params'
sudo perf probe 'hook_file_open%return $retval'
sudo perf record -e 'probe:*' -g -- ./nonet
sudo perf report
You can find the tool in my landlock-examples repo in the nonet_bug branch:
https://github.com/gnoack/landlock-examples/blob/nonet_bug/nonet.c
Landlock is enabled like this:
https://github.com/gnoack/landlock-examples/blob/nonet_bug/sandbox_socket.c
Do you have a hunch what might be going on?
Thanks,
–Günther
