detect link up/down and its initiator with kprobe

kprobe.c

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/kprobes.h>
#include <linux/netdevice.h>
#include <linux/fs.h>
#include <linux/fs_struct.h>

/* For each probe you need to allocate a kprobe structure */
static struct kprobe kp = {
    .symbol_name    = "dev_change_flags",
};

#define BUFLEN 256

/* kprobe pre_handler: called just before the probed instruction is executed */
static int handler_pre(struct kprobe *p, struct pt_regs *regs)
{
    printk(KERN_INFO "pre_handler: dev_change_flags called with rdi=%p rsi=%p rdx=%p rcx=%p\n",
        (void *)regs->di, (void *)regs->si, (void *)regs->dx, (void *)regs->cx);

    if (regs->di) {
        char name[IFNAMSIZ + 1] = {0};
        memcpy(name, ((struct net_device *)regs->di)->name, IFNAMSIZ);
        printk(KERN_INFO "pre_handler: interface [%s] %s\n",
            name, (regs->si & IFF_UP ? "up" : "down"));

        if (current && current->fs) {
            char buf[BUFLEN] = {0};
            char *path = d_path(&current->fs->pwd, buf, BUFLEN);
            if (path && path >= buf && path < buf + BUFLEN)
                printk(KERN_INFO "pre_handler: process working dir: %s\n", path);
        }
        if (current && current->mm && current->mm->exe_file) {
            char buf[BUFLEN] = {0};
            char *path;
            struct file *exe_file = current->mm->exe_file;
            path_get(&exe_file->f_path);
            path = d_path(&exe_file->f_path, buf, BUFLEN);
            if (path && path >= buf && path < buf + BUFLEN)
                printk(KERN_INFO "pre_handler: process exe path: %s\n", path);
        }

        printk(KERN_INFO "pre_handler: stack dump: ");
        dump_stack();
    } else {
        printk(KERN_INFO "pre_handler: unexpected: rdi=0\n");
    }
    return 0;
}

/* kprobe post_handler: called after the probed instruction is executed */
static void handler_post(struct kprobe *p, struct pt_regs *regs,
                unsigned long flags)
{
}

/*
 * fault_handler: this is called if an exception is generated for any
 * instruction within the pre- or post-handler, or when Kprobes
 * single-steps the probed instruction.
 */
static int handler_fault(struct kprobe *p, struct pt_regs *regs, int trapnr)
{
    printk(KERN_INFO "fault_handler: p->addr = 0x%p, trap #%dn",
        p->addr, trapnr);
    /* Return 0 because we don't handle the fault. */
    return 0;
}

static int __init kprobe_init(void)
{
    int ret;
    kp.pre_handler = handler_pre;
    kp.post_handler = handler_post;
    kp.fault_handler = handler_fault;

    ret = register_kprobe(&kp);
    if (ret < 0) {
        printk(KERN_INFO "register_kprobe failed, returned %d\n", ret);
        return ret;
    }
    printk(KERN_INFO "Planted kprobe at %p\n", kp.addr);
    return 0;
}

static void __exit kprobe_exit(void)
{
    unregister_kprobe(&kp);
    printk(KERN_INFO "kprobe at %p unregistered\n", kp.addr);
}

module_init(kprobe_init)
module_exit(kprobe_exit)
MODULE_LICENSE("GPL");