Problem to create char based on buffer and length in kernel module

Question

I try to get strings from userspace within the kernel module. Till I set my char size manually it seems working properly. However, I need to make it dynamic so if I use len parameter it shows weird symbols on the end of char.

static ssize_t msecurity_write(struct file *filep, const char *buffer, size_t len, loff_t *offset){
  
    char chars[12];
    if(copy_from_user(chars,buffer,len)){
        return -EFAULT;
    }

    printk(KERN_ALERT "Output> %s", chars);
    printk(KERN_ALERT "lengh> %i", len);

    return len;
 
}

First output is for char[len] secound has been set manualy char[12]. Even if you print len it shows value of 12.

Does this answer your question? Convert char array to string use C — Tsyvarev
– Tsyvarev, Commented Dec 7, 2020 at 15:59

ChrisBD · Accepted Answer · 2020-12-07 10:31:20Z

0

C strings are terminated by a null character. This character is not included in any string length calculation but must be included.

Thus a string of length 12 will need 13 bytes with the last byte equal to 0.

answered Dec 7, 2020 at 10:31

ChrisBD

9,2393 gold badges25 silver badges36 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Problem to create char based on buffer and length in kernel module

1 Answer 1

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related