6/4/2024 11:22 PM, Günther Noack wrote:
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?
Hello Günther!
Big thanks for this research!
I figured out that I define LANDLOCK_SHIFT_ACCESS_SOCKET macro in
really strange way (see landlock/limits.h):
#define LANDLOCK_SHIFT_ACCESS_SOCKET LANDLOCK_NUM_ACCESS_SOCKET
With this definition, socket access mask overlaps the fs access
mask in ruleset->access_masks[layer_level]. That's why
landlock_get_fs_access_mask() returns non-zero mask in hook_file_open().
So, the macro must be defined in this way:
#define LANDLOCK_SHIFT_ACCESS_SOCKET (LANDLOCK_NUM_ACCESS_NET +
LANDLOCK_NUM_ACCESS_FS)
With this fix, open() doesn't fail in your example.
I'm really sorry that I somehow made such a stupid typo. I will try my
best to make sure this doesn't happen again.
Thanks,
–Günther
