Fix random "personality" corruption when linking against lxc 6

[thomasjfox]

When using python3-lxc with liblxc from lxc 6.0.x, we could observe random systemd startup failures on containers.

systemd will report this on startup when the corruption hit: "Warning! Reported kernel version 2.6.74-300.fc42.x86_64 is older than systemd's required baseline kernel version 4.15. Your mileage may vary."

Some systemd services fail to start properly, including systemd-journald.

The root problem is that other lxc library code unexpectedly calls into lxc_config_parse_arch() from python3-lxc instead of the function from liblxc.

The function signature of lxc_config_parse_arch() changed throughout the years and the second "persona" pointer argument was added. The older python3-lxc copy of the function would not initialize the provided memory location of "persona". It will therefore contain a random value.

Additionally the symbol visibility of liblxc's lxc_config_parse_arch() changed with this commit in lxc 6.0:

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commit 42eeffcb05c468fd7b3a90eeda4a3abe9f26844b
AuthorDate: Sun Feb 18 15:43:20 2024 +0100

confile: unhide lxc_config_parse_arch() helper

Looks safe enough to be available for liblxc users.

---

This results in two symbols with the same name and the python3-lxc symbol takes precedence.

Fix the issue by making the function static in python3-lxc, so python3-lxc stays compatible with lxc 5.x and 6.x.

A future python3-lxc version might remove the local function and use lxc_config_parse_arch() from liblxc 6.0 and later.

Side quest: Even though lxc 5.0 already has the "persona" function argument in lxc_config_parse_arch() since 7c43fa56e70c65607f63dec8ff5a9682a3091ab2 (from 2021), it is not affected since the symbol visibility is still hidden.

[stgraber]

@thomasjfox can you change your commit message to include the required Signed-off-by: Firstname Lastname <email> line?

See https://github.com/lxc/lxc/blob/main/CONTRIBUTING for details

[thomasjfox]

Additional minimized C reproducer code lxc-start-c6.c:

#include <lxc/lxccontainer.h>
#include <stdio.h>
#include <sys/wait.h>
#include <sched.h>

signed long lxc_config_parse_arch(const char *arch)
{
    printf("Called wrong lxc_config_parse_arch\n");

    return 0;
}

int main(void)
{
    struct lxc_container *cont = lxc_container_new("c6", NULL);
    cont->want_close_all_fds(cont, true);

    cont->want_daemonize(cont, false);

    cont->start(cont, 0, NULL);

    printf("State: %s\n", cont->state(cont));

    return 0;
}

Compile with:
gcc lxc-start-c6.c -llxc

Just start and stop the container a few times and the issue will trigger. Tested on a Fedora 42 host machine.

[thomasjfox]

@thomasjfox can you change your commit message to include the required Signed-off-by: Firstname Lastname <email> line?

See https://github.com/lxc/lxc/blob/main/CONTRIBUTING for details

fixed, thanks. I saw it was missing when the commit hook started complaining. :)

[stgraber]

Thanks!

[thomasjfox]

Thanks for the quick merge.