Quelle fail_function.c Sprache: C

// SPDX-License-Identifier: GPL-2.0
/*
* fail_function.c: Function-based error injection
*/
#include <linux/error-injection.h>
#include <linux/debugfs.h>
#include <linux/fault-inject.h>
#include <linux/kallsyms.h>
#include <linux/kprobes.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <linux/uaccess.h>

static int fei_kprobe_handler(struct kprobe *kp, struct pt_regs *regs);

static void fei_post_handler(struct kprobe *kp, struct pt_regs *regs,
        unsigned long flags)
{
/*
* A dummy post handler is required to prohibit optimizing, because
* jump optimization does not support execution path overriding.
*/
}

struct fei_attr {
struct list_head list;
struct kprobe kp;
unsigned long retval;
};
static DEFINE_MUTEX(fei_lock);
static LIST_HEAD(fei_attr_list);
static DECLARE_FAULT_ATTR(fei_fault_attr);
static struct dentry *fei_debugfs_dir;

static unsigned long adjust_error_retval(unsigned long addr, unsigned long retv)
{
switch (get_injectable_error_type(addr)) {
case EI_ETYPE_NULL:
  return 0;
case EI_ETYPE_ERRNO:
  if (retv < (unsigned long)-MAX_ERRNO)
   return (unsigned long)-EINVAL;
  break;
case EI_ETYPE_ERRNO_NULL:
  if (retv != 0 && retv < (unsigned long)-MAX_ERRNO)
   return (unsigned long)-EINVAL;
  break;
case EI_ETYPE_TRUE:
  return 1;
}

return retv;
}

static struct fei_attr *fei_attr_new(const char *sym, unsigned long addr)
{
struct fei_attr *attr;

attr = kzalloc(sizeof(*attr), GFP_KERNEL);
if (attr) {
  attr->kp.symbol_name = kstrdup(sym, GFP_KERNEL);
  if (!attr->kp.symbol_name) {
   kfree(attr);
   return NULL;
  }
  attr->kp.pre_handler = fei_kprobe_handler;
  attr->kp.post_handler = fei_post_handler;
  attr->retval = adjust_error_retval(addr, 0);
  INIT_LIST_HEAD(&attr->list);
}
return attr;
}

static void fei_attr_free(struct fei_attr *attr)
{
if (attr) {
  kfree(attr->kp.symbol_name);
  kfree(attr);
}
}

static struct fei_attr *fei_attr_lookup(const char *sym)
{
struct fei_attr *attr;

list_for_each_entry(attr, &fei_attr_list, list) {
  if (!strcmp(attr->kp.symbol_name, sym))
   return attr;
}

return NULL;
}

static bool fei_attr_is_valid(struct fei_attr *_attr)
{
struct fei_attr *attr;

list_for_each_entry(attr, &fei_attr_list, list) {
  if (attr == _attr)
   return true;
}

return false;
}

static int fei_retval_set(void *data, u64 val)
{
struct fei_attr *attr = data;
unsigned long retv = (unsigned long)val;
int err = 0;

mutex_lock(&fei_lock);
/*
* Since this operation can be done after retval file is removed,
* It is safer to check the attr is still valid before accessing
* its member.
*/
if (!fei_attr_is_valid(attr)) {
  err = -ENOENT;
  goto out;
}

if (attr->kp.addr) {
  if (adjust_error_retval((unsigned long)attr->kp.addr,
     val) != retv)
   err = -EINVAL;
}
if (!err)
  attr->retval = val;
out:
mutex_unlock(&fei_lock);

return err;
}

static int fei_retval_get(void *data, u64 *val)
{
struct fei_attr *attr = data;
int err = 0;

mutex_lock(&fei_lock);
/* Here we also validate @attr to ensure it still exists. */
if (!fei_attr_is_valid(attr))
  err = -ENOENT;
else
  *val = attr->retval;
mutex_unlock(&fei_lock);

return err;
}
DEFINE_DEBUGFS_ATTRIBUTE(fei_retval_ops, fei_retval_get, fei_retval_set,
    "%llx\n");

static void fei_debugfs_add_attr(struct fei_attr *attr)
{
struct dentry *dir;

dir = debugfs_create_dir(attr->kp.symbol_name, fei_debugfs_dir);

debugfs_create_file("retval", 0600, dir, attr, &fei_retval_ops);
}

static void fei_debugfs_remove_attr(struct fei_attr *attr)
{
debugfs_lookup_and_remove(attr->kp.symbol_name, fei_debugfs_dir);
}

static int fei_kprobe_handler(struct kprobe *kp, struct pt_regs *regs)
{
struct fei_attr *attr = container_of(kp, struct fei_attr, kp);

if (should_fail(&fei_fault_attr, 1)) {
  regs_set_return_value(regs, attr->retval);
  override_function_with_return(regs);
  return 1;
}

return 0;
}
NOKPROBE_SYMBOL(fei_kprobe_handler)

static void *fei_seq_start(struct seq_file *m, loff_t *pos)
{
mutex_lock(&fei_lock);
return seq_list_start(&fei_attr_list, *pos);
}

static void fei_seq_stop(struct seq_file *m, void *v)
{
mutex_unlock(&fei_lock);
}

static void *fei_seq_next(struct seq_file *m, void *v, loff_t *pos)
{
return seq_list_next(v, &fei_attr_list, pos);
}

static int fei_seq_show(struct seq_file *m, void *v)
{
struct fei_attr *attr = list_entry(v, struct fei_attr, list);

seq_printf(m, "%ps\n", attr->kp.addr);
return 0;
}

static const struct seq_operations fei_seq_ops = {
.start = fei_seq_start,
.next = fei_seq_next,
.stop = fei_seq_stop,
.show = fei_seq_show,
};

static int fei_open(struct inode *inode, struct file *file)
{
return seq_open(file, &fei_seq_ops);
}

static void fei_attr_remove(struct fei_attr *attr)
{
fei_debugfs_remove_attr(attr);
unregister_kprobe(&attr->kp);
list_del(&attr->list);
fei_attr_free(attr);
}

static void fei_attr_remove_all(void)
{
struct fei_attr *attr, *n;

list_for_each_entry_safe(attr, n, &fei_attr_list, list) {
  fei_attr_remove(attr);
}
}

static ssize_t fei_write(struct file *file, const char __user *buffer,
    size_t count, loff_t *ppos)
{
struct fei_attr *attr;
unsigned long addr;
char *buf, *sym;
int ret;

/* cut off if it is too long */
if (count > KSYM_NAME_LEN)
  count = KSYM_NAME_LEN;

buf = memdup_user_nul(buffer, count);
if (IS_ERR(buf))
  return PTR_ERR(buf);

sym = strstrip(buf);

mutex_lock(&fei_lock);

/* Writing just spaces will remove all injection points */
if (sym[0] == '\0') {
  fei_attr_remove_all();
  ret = count;
  goto out;
}
/* Writing !function will remove one injection point */
if (sym[0] == '!') {
  attr = fei_attr_lookup(sym + 1);
  if (!attr) {
   ret = -ENOENT;
   goto out;
  }
  fei_attr_remove(attr);
  ret = count;
  goto out;
}

addr = kallsyms_lookup_name(sym);
if (!addr) {
  ret = -EINVAL;
  goto out;
}
if (!within_error_injection_list(addr)) {
  ret = -ERANGE;
  goto out;
}
if (fei_attr_lookup(sym)) {
  ret = -EBUSY;
  goto out;
}
attr = fei_attr_new(sym, addr);
if (!attr) {
  ret = -ENOMEM;
  goto out;
}

ret = register_kprobe(&attr->kp);
if (ret) {
  fei_attr_free(attr);
  goto out;
}
fei_debugfs_add_attr(attr);
list_add_tail(&attr->list, &fei_attr_list);
ret = count;
out:
mutex_unlock(&fei_lock);
kfree(buf);
return ret;
}

static const struct file_operations fei_ops = {
.open =  fei_open,
.read =  seq_read,
.write = fei_write,
.llseek = seq_lseek,
.release = seq_release,
};

static int __init fei_debugfs_init(void)
{
struct dentry *dir;

dir = fault_create_debugfs_attr("fail_function", NULL,
     &fei_fault_attr);
if (IS_ERR(dir))
  return PTR_ERR(dir);

/* injectable attribute is just a symlink of error_inject/list */
debugfs_create_symlink("injectable", dir, "../error_injection/list");

debugfs_create_file("inject", 0600, dir, NULL, &fei_ops);

fei_debugfs_dir = dir;

return 0;
}

late_initcall(fei_debugfs_init);

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