mirror of
https://github.com/cirosantilli/linux-kernel-module-cheat.git
synced 2026-01-13 20:12:26 +00:00
92 lines
2.5 KiB
C
92 lines
2.5 KiB
C
/*
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Input: an integer (with some annoying restrictions) and a pointer
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Output:
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- positive integer return value, which for sanity should only be used with negative values for success
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- the input pointer data may be overwritten to contain output
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Feels like an archaic API... so many weird restrictions and types for something that could be so simple!
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Documentation/ioctl/ioctl-number.txt has some info:
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_IO an ioctl with no parameters
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_IOW an ioctl with write parameters (copy_from_user)
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_IOR an ioctl with read parameters (copy_to_user)
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_IOWR an ioctl with both write and read parameters.
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- https://stackoverflow.com/questions/2264384/how-do-i-use-ioctl-to-manipulate-my-kernel-module/44613896#44613896
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- https://askubuntu.com/questions/54239/problem-with-ioctl-in-a-simple-kernel-module/926675#926675
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*/
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#include <asm/uaccess.h> /* copy_from_user, copy_to_user */
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#include <linux/debugfs.h>
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#include <linux/module.h>
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#include <linux/printk.h> /* printk */
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#include "ioctl.h"
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static struct dentry *debugfs_file;
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static long unlocked_ioctl(struct file *filp, unsigned int cmd, unsigned long argp)
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{
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void __user *arg_user;
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union {
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int i;
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lkmc_ioctl_struct s;
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} arg_kernel;
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arg_user = (void __user *)argp;
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pr_info("cmd = %x\n", cmd);
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switch (cmd) {
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case LKMC_IOCTL_INC:
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if (copy_from_user(&arg_kernel.i, arg_user, sizeof(arg_kernel.i))) {
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return -EFAULT;
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}
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pr_info("0 arg = %d\n", arg_kernel.i);
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arg_kernel.i += 1;
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if (copy_to_user(arg_user, &arg_kernel.i, sizeof(arg_kernel.i))) {
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return -EFAULT;
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}
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break;
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case LKMC_IOCTL_INC_DEC:
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if (copy_from_user(&arg_kernel.s, arg_user, sizeof(arg_kernel.s))) {
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return -EFAULT;
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}
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pr_info("1 arg = %d %d\n", arg_kernel.s.i, arg_kernel.s.j);
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arg_kernel.s.i += 1;
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arg_kernel.s.j -= 1;
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if (copy_to_user(arg_user, &arg_kernel.s, sizeof(arg_kernel.s))) {
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return -EFAULT;
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}
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break;
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default:
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return -EINVAL;
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break;
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}
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return 0;
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}
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static const struct file_operations fops = {
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.owner = THIS_MODULE,
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.unlocked_ioctl = unlocked_ioctl
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};
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static int myinit(void)
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{
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/* ioctl permissions are not automatically restricted by rwx as for read / write,
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* but we could of course implement that ourselves:
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* https://stackoverflow.com/questions/29891803/user-permission-check-on-ioctl-command */
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debugfs_file = debugfs_create_file("lkmc_ioctl", 0, NULL, NULL, &fops);
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return 0;
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}
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static void myexit(void)
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{
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debugfs_remove(debugfs_file);
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}
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module_init(myinit)
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module_exit(myexit)
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MODULE_LICENSE("GPL");
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