3rd-party/linux-kernel-module-cheat
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kernel modules: add a quick scull port from LDD3

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* fix fops.c on both kernels:
  * 5.9: the out of space error code was 1 not 8
  * 6.6: for whatever reason we can't read the user buffer as before on the
         diagnostic print, it leads to segfault and oops
* create memfile.c which is like fops.c but of unlimited size
This commit is contained in:
Ciro Santilli
2025-04-28 15:23:44 +01:00
parent 3d84eccc43
commit e4847e4b40
16 changed files with 2133 additions and 50 deletions
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49
kernel_modules/fops.c
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@@ -1,4 +1,4 @@
/* https://cirosantilli.com/linux-kernel-module-cheat#file-operations */
/* https://cirosantilli.com/linux-kernel-module-cheat#fops */
#include <linux/debugfs.h>
#include <linux/errno.h> /* EFAULT */
@@ -10,7 +10,15 @@
#include <uapi/linux/stat.h> /* S_IRUSR */
static struct dentry *debugfs_file;
// The buffer can be stored in two ways: static module data or kmalloc.
#define STATIC 1
#if STATIC
static char data[] = {'a', 'b', 'c', 'd'};
#define BUFLEN sizeof(data)
#else
static char *data;
#define BUFLEN 4
#endif
static int open(struct inode *inode, struct file *filp)
{
@@ -19,7 +27,7 @@ static int open(struct inode *inode, struct file *filp)
}
/* @param[in,out] off: gives the initial position into the buffer.
* We must increment this by the ammount of bytes read.
* We must increment this by the amount of bytes read.
* Then when userland reads the same file descriptor again,
* we start from that point instead.
*/
@@ -27,21 +35,18 @@ static ssize_t read(struct file *filp, char __user *buf, size_t len, loff_t *off
{
ssize_t ret;
pr_info("read\n");
pr_info("len = %zu\n", len);
pr_info("off = %lld\n", (long long)*off);
if (sizeof(data) <= *off) {
pr_info("read len=%zu off=%lld\n", len, (long long)*off);
if (BUFLEN <= *off) {
ret = 0;
} else {
ret = min(len, sizeof(data) - (size_t)*off);
ret = min(len, BUFLEN - (size_t)*off);
if (copy_to_user(buf, data + *off, ret)) {
ret = -EFAULT;
} else {
*off += ret;
}
}
pr_info("buf = %.*s\n", (int)len, buf);
pr_info("ret = %lld\n", (long long)ret);
pr_info("ret=%lld\n", (long long)ret);
return ret;
}
@@ -54,13 +59,11 @@ static ssize_t write(struct file *filp, const char __user *buf, size_t len, loff
{
ssize_t ret;
pr_info("write\n");
pr_info("len = %zu\n", len);
pr_info("off = %lld\n", (long long)*off);
if (sizeof(data) <= *off) {
pr_info("write len=%zu off=%lld\n", len, (long long)*off);
if (BUFLEN <= *off) {
ret = 0;
} else {
if (sizeof(data) - (size_t)*off < len) {
if (BUFLEN - (size_t)*off < len) {
ret = -ENOSPC;
} else {
if (copy_from_user(data + *off, buf, len)) {
@@ -89,9 +92,7 @@ static loff_t llseek(struct file *filp, loff_t off, int whence)
{
loff_t newpos;
pr_info("llseek\n");
pr_info("off = %lld\n", (long long)off);
pr_info("whence = %lld\n", (long long)whence);
pr_info("llseek off=%lld whence=%lld\n", (long long)off, (long long)whence);
switch(whence) {
case SEEK_SET:
newpos = off;
@@ -100,7 +101,7 @@ static loff_t llseek(struct file *filp, loff_t off, int whence)
newpos = filp->f_pos + off;
break;
case SEEK_END:
newpos = sizeof(data) + off;
newpos = BUFLEN + off;
break;
default:
return -EINVAL;
@@ -124,12 +125,24 @@ static const struct file_operations fops = {
static int myinit(void)
{
#if STATIC == 0
data = kmalloc(BUFLEN, GFP_KERNEL);
if (!data)
return -ENOMEM;
data[0] = 'a';
data[1] = 'b';
data[2] = 'c';
data[3] = 'd';
#endif
debugfs_file = debugfs_create_file("lkmc_fops", S_IRUSR | S_IWUSR, NULL, NULL, &fops);
return 0;
}
static void myexit(void)
{
#if STATIC == 0
kfree(data);
#endif
debugfs_remove_recursive(debugfs_file);
}