rust - 如何通过 libc::getgroups 为用户获取组？

Question

extern crate libc;

fn example(guid: u32) {
    unsafe {
        let ruid = libc::getuid();
        libc::seteuid(guid);
        let mut v = vec![0; 0];
        let num_groups = libc::getgroups(0, v.as_mut_ptr());
        let mut groups = Vec::with_capacity(num_groups as usize);
        libc::getgroups(num_groups, groups.as_mut_ptr());
        println!(
            "real user id {} as user id {}, as user groups {:?}, numgroups {}",
            &ruid, &guid, &groups, &num_groups
        );
    }
}

这打印

real user id 1000 as user id 1000, as user groups [], numgroups 9

我的假设是它会显示一个包含 9 组的向量。

Answer 1

您需要通过添加虚拟元素来更改 groups 的大小，而不仅仅是它的容量。像这样:

unsafe {
    let ruid = libc::getuid();
    let guid = libc::getgid();
    let num_groups = libc::getgroups(0, ::std::ptr::null_mut());
    let mut groups = vec![0; num_groups as usize];
    libc::getgroups(num_groups, groups.as_mut_ptr());
    println!(
        "real user id {} as user id {}, as user groups {:?}, numgroups {}",
        &ruid, &guid, &groups, &num_groups
    );
}