从bprm获取命令行参数

在LSM钩子中获取到linux_binprm结构，从中获取到命令行参数。

static int get_argv_from_bprm(struct linux_binprm *bprm)
{
    int ret = 0;
    unsigned long offset, pos;
    char *kaddr;
    struct page *page;
    char argv[PAGE_SIZE] = {0};
    int i = 0;
    int argc = 0;
    int count = 0;
    if (!bprm)
        return 0;

    argc = bprm->argc;

    pos = bprm->p;
    do {
        offset = pos & ~PAGE_MASK;
        page = get_arg_page(bprm, pos, 0);
        if (!page) {
            ret = 0;
            goto out;
        }
        kaddr = kmap_atomic(page);

        for (i = 0; offset < PAGE_SIZE && count < argc && i < PAGE_SIZE; offset++, pos++) {
            if (kaddr[offset] == '\0') {
                count++;
                pos++;
                printk("argv is %s\n", argv);
                memset(argv, 0, sizeof(argv));
                i = 0;
                continue;
            }
            argv[i] = kaddr[offset];
            i++;
        }

        kunmap_atomic(kaddr);
        put_arg_page(page);
    } while (offset == PAGE_SIZE);

    ret = 0;

out:
    return ret;
}