I'm trying to print TCP address but I'm getting "Dereferencing pointer to incomplete type" error. I think iphdr typecasting is not working. How do I fix this issue?
unsigned int hook_func(unsigned int hooknum,
struct sk_buff *skb,
const struct net_device *in,
const struct net_device *out,
int (*okfn)(struct sk_buff *))
{
struct iphdr *ip_header; // ip header struct
if (!skb)
return NF_ACCEPT;
ip_header = (struct iphdr *)skb_network_header(skb); /* I think this is not working */
printk("addr : %lu.\n",ip_header->saddr);
return NF_ACCEPT;
}
int init_module()
{
printk(KERN_INFO "initialize kernel module\n");
/* Fill in our hook structure */
nfho.hook = hook_func; /* Handler function */
nfho.hooknum = NF_INET_PRE_ROUTING; /* First hook for IPv4 */
nfho.pf = PF_INET;
nfho.priority = NF_IP_PRI_FIRST; /* Make our function first */
nf_register_hook(&nfho);
return 0;
}
For dereferece pointer of type struct iphdr you need
#include <linux/ip.h>
(Actually, this type is defined in include/uapi/linux/ip.h, but usually headers under uapi/ are included via other ones.)
Related
Disclaimer - I have to admit that it's the 1'st time I'm using this kernel interface (socket).
I'm currently working on a design of a kernel module that is based on a netlink socket .
I'm using Ubuntu14.04 and linux kernel 4.
As a starter, I wanted to make sure that I can use the netlink socket in both directions.
I've written an application that does the following:
1) User send a message to kernel via the netlink socket.
2) Kernel, upon receiving the message – sends "ABCD" string message to a workqueue.
3) When the "ABCD" message is received by the workqueue, it calls a function (named - my_wq_function) which send it back to the user space via netlink socket.
4) In the user space I'm using a recvmsg function (blocking until a message is received) and displays the "ABCD" message.
My problem is that the return value from the recvmsg function is 20 (instead of 4), and the data itself (i.e. NLMSG_DATA) is empty.
During the debug I tried to change the message to "ABCD1234" and got a return value of 24 bytes, however the data is still empty.
I also verified that my entire path until the point of sending the "ABCD" from kernel to the socket is OK.
Not sure what I'm doing wrong here & will highly appreciate your help.
Thanks in advance, MotiC.
my code example can be found below:
User space code:
printf("netlink receiver thread started...\n");
nlh_rcv = (struct nlmsghdr *)malloc(NLMSG_SPACE(MAX_PAYLOAD));
while(true) //endless loop on netlink socket
{
memset(nlh_rcv, 0, NLMSG_SPACE(MAX_PAYLOAD));
iov_rcv.iov_base = (void *)nlh_rcv;
iov_rcv.iov_len = nlh_rcv->nlmsg_len;
msg_rcv.msg_name = (void *)&dest_addr;
msg_rcv.msg_namelen = sizeof(dest_addr);
msg_rcv.msg_iov = &iov;
msg_rcv.msg_iovlen = 1;
ret=recvmsg(sock_fd, &msg_rcv, 0);
printf("errno=%i bytes=%i message from kernel: %s\n",errno, ret, (char*)NLMSG_DATA(nlh_rcv));
uint8_t mymsg[100];
memcpy(mymsg, NLMSG_DATA(nlh_rcv), 100);
printf("message from kernel: %s\n",mymsg);
}
Kernel space code:
#include <linux/module.h> /* Needed by all modules */
#include <linux/kernel.h> /* Needed for KERN_INFO */
#include <linux/init.h> /* Needed for the macros */
#include <net/sock.h>
#include <linux/socket.h>
#include <linux/net.h>
#include <asm/types.h>
#include <linux/netlink.h>
#include <linux/skbuff.h>
#include <linux/workqueue.h>
MODULE_LICENSE("GPL");
#include "rf_Kdriver_main.h"
//------ definitions ------------------------------------------------------------------------------------------------------------
#define NETLINK_USER 31
#define MAX_PAYLOAD 1024 /* maximum payload size*/
struct sock *nl_sk = NULL;
struct nlmsghdr *nlh;
struct nlmsghdr *nlh_out;
struct sk_buff *skb_out;
char buf_to_user[100];
int pid;
//------------------------------------------------------------------------------------------------------------------------------
struct workqueue_struct *my_wq;
typedef struct {
struct work_struct my_work;
uint8_t msg_to_pc[128];
uint8_t msg_len;
} my_work_t;
my_work_t *work, *work2;
//-----------------------------------------------------------------------------------------------------------------------------
static void my_wq_function( struct work_struct *work)
{
int res;
my_work_t *my_work = (my_work_t *)work;
skb_out = nlmsg_new(my_work->msg_len,0);
if (!skb_out)
{
printk("Failed to allocate new skb\n");
return;
}
nlh_out = nlmsg_put(skb_out, 0, 0, NLMSG_DONE,my_work->msg_len, 0);
NETLINK_CB(skb_out).dst_group = 0;
memcpy((char*)NLMSG_DATA(nlh_out), my_work->msg_to_pc , my_work->msg_len);
printk( "dequeue message to pc=%s len=%i\n", (char*)NLMSG_DATA(nlh_out), (int)strlen((char*)NLMSG_DATA(nlh_out)));
res = nlmsg_unicast(nl_sk, skb_out, pid);
if (res<0)
printk("Failed to send message from kernel to user\n");
kfree( (void *)work );
return;
}
//-----------------------------------------------------------------------------------------------------------------------------
int send_up_msg_to_workque(uint8_t msg_to_pc[], uint8_t msg_len)
{
int ret=0;
work = (my_work_t *)kmalloc(sizeof(my_work_t), GFP_KERNEL);
if (work) {
INIT_WORK( (struct work_struct *)work, my_wq_function );
memcpy(work->msg_to_pc, msg_to_pc, msg_len);
work->msg_len = msg_len;
ret = queue_work( my_wq, /*(struct work_struct *)RR*/work );
printk("kuku ret=%i msg=%s\n",ret,work->msg_to_pc);
}
return ret;
}
//------------------------------------------------------------------------------------------------------------------------------
static void netlink_recv_msg(struct sk_buff *skb)
{
char *msg = "ABCD1234";
printk(KERN_INFO "Entering: %s\n", __FUNCTION__);
nlh=(struct nlmsghdr*)skb->data;
printk(KERN_INFO "Netlink at kernel received msg payload: %s\n",(char*)NLMSG_DATA(nlh));
//rr
pid = nlh->nlmsg_pid;
send_up_msg_to_workque((uint8_t*) msg, strlen(msg));
}
//-------------------------------------------------------------------------------------------------------------------------------------
struct netlink_kernel_cfg cfg = {
.input = netlink_recv_msg,
};
static int __init rf_driver_start(void)
{
printk(KERN_INFO "Loading RF Driver module1...\n");
my_wq = create_workqueue("my_queue");
if (!my_wq)
{
printk("Failed to create work queue\n");
}
printk("Entering: %s\n",__FUNCTION__);
nl_sk = netlink_kernel_create(&init_net, NETLINK_USER, &cfg);
if(!nl_sk)
{
printk(KERN_ALERT "Error creating socket.\n");
return -10;
}
return 0;
}
//--------------------------------------------------------------------------------------------------------------
static void __exit rf_driver_end(void)
{
netlink_kernel_release(nl_sk);
flush_workqueue(my_wq);
destroy_workqueue(my_wq);
printk(KERN_INFO "RF Driver exit...\n");
}
module_init(rf_driver_start);
module_exit(rf_driver_end);
Update,
I changed my user space function to:
char buf[100];
ret=recv(sock_fd, buf, 100, 0);
instead of:
ret=recvmsg(sock_fd, &msg_rcv, 0);
and it works...
does anyone have an idea regarding this strange behavior ?
Thanks.
Can you please paste complete userspace code.
I guess 'len' int this code is the issue:
memset(nlh_rcv, 0, NLMSG_SPACE(MAX_PAYLOAD));
iov_rcv.iov_len = nlh_rcv->nlmsg_len; << check to what value is it getting initialized.
I implement mmap function, and mount it to file operation.
And create a file in /proc.
but when I insmod, it responses "mmap_example2: Unknown symbol _page_cachable_default
insmod: can't insert 'mmap_example2.ko': unknown symbol in module, or unknown parameter"
when i remove mmap function from file operations, it can be inserted.
so do i neglect something? how to make mmap work in procfs?
the code is below
#include <linux/init.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/proc_fs.h>
#include <linux/vmalloc.h>
#define FILE_NAME "test"
typedef enum ALLOC_TYPE
{
KMALLOC = 0, VMALLOC, MAX_ALLOC_TYPE,
} eAllocType;
static unsigned char array[10]={0,1,2,3,4,5,6,7,8,9};
static unsigned char *buffer;
static int file_open(struct inode *pInode, struct file *pFile)
{
printk("%s\n", __FUNCTION__);
return 0;
}
static int file_release(struct inode *pInode, struct file *pFile)
{
printk("%s\n", __FUNCTION__);
return 0;
}
static int file_mmap(struct file *pFile, struct vm_area_struct* pVMA)
{
unsigned long page;
unsigned char i;
unsigned long start = (unsigned long)pVMA->vm_start;
unsigned long size = (unsigned long)(pVMA->vm_end - pVMA->vm_start);
page = virt_to_phys(buffer);
if(remap_pfn_range(pVMA,start,page>>PAGE_SHIFT,size,PAGE_SHARED))
return -1;
for(i=0;i<10;i++)
buffer[i] = array[i];
return 0;
}
struct file_operations file_ops =
{
.open = file_open,
.release = file_release,
.mmap = file_mmap,
};
static int mmap_example2_init(void)
{
struct proc_dir_entry* entry = NULL;
printk("%s init\n", __FUNCTION__);
if(!(entry = create_proc_entry(FILE_NAME,0666,NULL)))
{
printk("%s fail to create proc file\n",__FUNCTION__);
return -EINVAL;
}
entry->proc_fops = &file_ops;
buffer = kmalloc(10,GFP_KERNEL);
if (!buffer)
{
printk("allocate mem error\n");
return -1;
}
SetPageReserved(virt_to_page(buffer));
return 0;
}
static void mmap_example2_exit(void)
{
printk("%s exit\n", __FUNCTION__);
remove_proc_entry(FILE_NAME,NULL);
ClearPageReserved(virt_to_page(buffer));
kfree(buffer);
}
module_init(mmap_example2_init);
module_exit(mmap_example2_exit);
To add file_operations use proc_create instead of create_proc_entry and pass it your file_operation object
static struct file_operations myops =
{
.read = myread,
.mmap = mymmap,
};
static int simple_init(void)
{
ent=proc_create("mytest",0660,NULL,&myops);
printk(KERN_ALERT "hello, module %d...\n",irq);
return 0;
}
I was testing the network hook code given in https://en.wikipedia.org/wiki/Hooking . My kernel version is 3.11.
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/skbuff.h>
#include <net/ip.h>
#include <linux/ip.h>
#include <linux/tcp.h>
#include <linux/in.h>
#include <linux/netfilter.h>
#include <linux/netfilter_ipv4.h>
/* Port we want to drop packets on */
static const uint16_t port = 25;
/* This is the hook function itself */
static unsigned int hook_func(unsigned int hooknum,
struct sk_buff **pskb,
const struct net_device *in,
const struct net_device *out,
int (*okfn)(struct sk_buff *)){
struct iphdr *iph = ip_hdr(*pskb);
struct tcphdr *tcph, tcpbuf;
if (iph->protocol != IPPROTO_TCP)
return NF_ACCEPT;
tcph = skb_header_pointer(*pskb, ip_hdrlen(*pskb), sizeof(*tcph), &tcpbuf);
if (tcph == NULL)
return NF_ACCEPT;
return (tcph->dest == port) ? NF_DROP : NF_ACCEPT;
}
/* Used to register our hook function */
static struct nf_hook_ops nfho = {
.hook = hook_func,
.hooknum = NF_INET_PRE_ROUTING,
.pf = NFPROTO_IPV4,
.priority = NF_IP_PRI_FIRST,
};
static __init int my_init(void)
{
return nf_register_hook(&nfho);
}
static __exit void my_exit(void)
{
nf_unregister_hook(&nfho);
}
module_init(my_init);
module_exit(my_exit);
But after loading , the above code is freezing the system. Can anybody please tell, what is the reason for that?. I think that the above code might have already tested in some lower versions of kernel. So I doubt, some kernel parameters or features have been changed.
I am not able to allocate memory for nested structures using pointers.
What syntax should I use to allocate the memory for lots of structures that have pointers to other structures? How should I go about accessing the values in the structures once the memory is allocated?
struct A {
int *a;
struct B *b;
};
struct B {
int *b;
struct C *c;
};
struct C {
int *c;
struct D *d;
};
struct D {
int *d;
};
int main(int argc, const char* argv[]) {
struct A* foo;
/* Structure allocation */
/* use of structures */
}
I can't go beyond 2 nested structures. Beyond that I start getting Segmentation fault.
I tried something like this:
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
typedef struct file f1;
typedef struct command c1;
typedef struct arguments a1;
typedef struct ccity ccity;
typedef struct csub csub;
struct arguments {
char *argname;
struct arguments *next;
};
struct command {
char *cmdname;
struct arguments *args;
};
struct file{
int fileid;
char *filename;
struct command *cmd;
};
struct sub{
char *subname;
};
struct city {
char *city_name;
struct sub *s11;
};
struct road{
char *name;
struct city *next_city;
};
int main()
{
char name[] = "HELLO ";
struct file *f1;
struct city *c1 = NULL;
struct road *r1 = NULL;
struct sub *s1 = NULL;
printf("HELOOOOOOOOO");
f1->filename;
f1 = malloc(10*sizeof(struct file ));
f1->filename = (char *)malloc(10*sizeof(char *));
c1 = malloc(sizeof(c1));
r1 = malloc(sizeof(r1));
s1 = malloc(sizeof(s1));
r1->name = malloc(100*sizeof(char *));
r1->next_city = malloc(100*sizeof(r1->next_city));
c1->city_name = malloc(100*sizeof(char *));
c1->s11 = malloc(100*sizeof(c1->s11));
c1->s11->subname = calloc(120,sizeof(char*));
(*c1).s11->subname = "text";
(*r1).next_city->s11->subname =
malloc(10 * sizeof((*r1).next_city->s11->subname));
strncpy((*r1).next_city->s11->subname,"sant",4);
r1->name = malloc(sizeof(char *));
c1->city_name = malloc(sizeof(char *));
r1->next_city = malloc(sizeof(char *));
r1->next_city->city_name = "Hello";
/*strcpy(f1->filename,"file1");
printf("name is %s\n",(f1->filename));
c1->cmdname = (char *)malloc(10*sizeof(c1->cmdname));
strcpy(f1[0].cmd[0].cmdname,"command1");
printf("name is %s\n",f1[0].cmd[0].cmdname);
strcpy(f1[0].cmd[1].cmdname,"command2");
printf("name is %s\n",f1[0].cmd[1].cmdname);
strcpy(f1[0].cmd[2].cmdname,"command3");
printf("name is %s\n",f1[0].cmd[2].cmdname);
strcpy(f1[0].cmd[2].args[0].argname,"argument1");
printf("name is %s\n",f1[0].cmd[2].args[0].argname);
strcpy(f1[0].cmd[2].args[0].argname,"argument1");
printf("name is %s\n",f1[0].cmd[2].args[1].argname);
(f1[0].cmd[0].args[0]).argname = malloc(20*sizeof(char*));
strcpy((f1[0].cmd[0].args[0]).argname,"argument1");
printf("name is %s\n",(f1[0].cmd[0].args[0]).argname);
*/
}
The function
struct device * device_create ( struct class * class,
struct device * parent,
dev_t devt,
void * drvdata,
const char * fmt,
...);
[link to documentation] takes an argument "void * drvdata". It is described as "the data to be added to the device for callbacks". What callbacks exactly are meant here? The file-operation-functions?
SysFS is one example of where this could be useful: whenever userspace communicates with the driver using SysFS (see "Reading/Writing Attribute Data" in the documentation), the kernel calls the corresponding callbacks. The void * drvdata pointer supplied during device_create can then be obtained by calling dev_get_drvdata(dev). The pointer could be used to refer to a structure containing driver's state for example.
#include <linux/module.h> /* Needed by all modules */
#include <linux/kernel.h> /* Needed for KERN_INFO */
#include <linux/init.h> /* Needed for the macros */
#include <linux/device.h>
#include <linux/err.h>
MODULE_LICENSE("GPL");
static ssize_t show_period(struct device *dev, struct device_attribute *attr, char *buf);
static ssize_t set_period(struct device* dev,
struct device_attribute* attr,
const char* buf,
size_t count);
static DEVICE_ATTR(period, S_IWUSR | S_IRUSR, show_period, set_period);
static struct device *s_pDeviceObject;
static struct class *s_pDeviceClass;
static struct pwm_device_state
{
int m_Period;
} s_DeviceState;
static int __init pwmdriver_init(void)
{
int result;
s_pDeviceClass = class_create(THIS_MODULE, "pwmdriver");
BUG_ON(IS_ERR(s_pDeviceClass));
s_pDeviceObject = device_create(s_pDeviceClass, NULL, 0, &s_DeviceState, "channel");
result = device_create_file(s_pDeviceObject, &dev_attr_period);
BUG_ON(result < 0);
return result;
}
static ssize_t show_period(struct device *dev, struct device_attribute *attr, char *buf)
{
struct pwm_device_state *pwm_device_data;
pwm_device_data = dev_get_drvdata(dev);
return scnprintf(buf, PAGE_SIZE, "%d\n", pwm_device_data->m_Period);
}
static ssize_t set_period(struct device* dev,
struct device_attribute* attr,
const char* buf,
size_t count)
{
long period_value = 0;
struct pwm_device_state *pwm_device_data;
if (kstrtol(buf, 10, &period_value) < 0)
return -EINVAL;
if (period_value < 10) //Safety check
return -EINVAL;
pwm_device_data = dev_get_drvdata(dev);
pwm_device_data->m_Period = period_value;
return count;
}
static void __exit pwmdriver_exit(void)
{
device_remove_file(s_pDeviceObject, &dev_attr_period);
device_destroy(s_pDeviceClass, 0);
class_destroy(s_pDeviceClass);
}
module_init(pwmdriver_init);
module_exit(pwmdriver_exit);