Hi,
Someone are able to help-me with this doubts ?
1 -
>int uid;mm_segment_t old_fs;
>old_fs = get_fs();
>set_fs(get_ds());
>uid = __NR_getuid;
>printk("\nUID %d",uid);
>set_fs(old_fs);
I received this message:
libc-set_fs.o: unresolved symbol sys_getuid
So, if i change the sys_getuid() by _NR__getuid is
compile and load but the
output at printk() is completily wrong! Why ? :(
>yes, u would get that error because, you should be
using sys_getuid()
>rather than getuid() , since the kernel doesnt know
what getuid() is
>since, it is a userspace function, and after insmod
or rather during
>insmod your module is being linked with the kernel
,libc would
>internally call sys_getuid() which is transparent to
the user.
Ok, but in this case (if worked) i will be callin the
getuid. If i will call a syscall
(sys_*) i need use get_fs() and set_fs() ? Why if i'm
already in kernel-space ?
Anyway, doesn't exist a way to access libc functions ?
For example feof(), etc ?
2 - I want to get the name (and path) of program that
is running so i done like that:
printk("PID %d PROG %s",current->pid, current->comm);
The PID is showed correctily, but the PROG is always
empity! :( Why ?
3 - In the article we created a basic device driver
like that:
/*just a dummy for demonstration*/
static int driver_open(struct inode *i, struct file
*f){
printk("<1>Open Function\n");
return 0;
}
/*register every function which will be provided by
our driver*/
static struct file_operations fops = {
NULL, /*lseek*/
NULL, /*read*/
NULL, /*write*/
NULL, /*readdir*/
NULL, /*select*/
NULL, /*ioctl*/
NULL, /*mmap*/
driver_open, /*open, take a look at my dummy
open function*/
NULL, /*release*/
NULL /*fsync...*/
};
int init_module(void){
/*register driver with major 40 and the name driver*/
if(register_chrdev(40, "driver", &fops)) return -EIO;
return 0;
}
void cleanup_module(void){
/*unregister our driver*/
unregister_chrdev(40, "driver");
}
So i created the device with mknod and tryed "open"
with cat, echo, etc, but it never print the "Open
Function" from printk(), why ?
4 - Other intersting thing is that we can re-use
exported symbols, so i tryed to test and import the
vfat_rmdir and do it return 0 to doesn't remove my dir
over fat (only to test, to learn how to work import a
exported symbol), i done like that:
/* Get vfat_rmdir exported function */
extern int *vfat_rmdir_Rc0ad670e;
/* Our faked vfat_mkdir */
int *new_vfat_rmdir(struct inode *dir, struct dentry
*dentry){
return 0;
}
int init_module(void) {
vfat_rmdir_Rc0ad670e=new_vfat_rmdir;
return 0;
}
void cleanup_module(void){
}
And it really can't remove dir under fat with "rm",
but when i type "rm" i receive a dump from kernel, and
i can't access more fat fs! :(
Why ? What i done wrong ?
Thkz a lot and sorry for idiot questions.
Regards
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