Using strsep in kernel space to separate a string

Question

I'm trying to separate a string based on some delimeter in a kernel module.

I'm trying to use the strsep() function, but when I try to use it my kernel crashes.

Can someone identify the bug in the code below?

char *test = "test1:test2:test3";
char *token = test;
char *end = test;
while (token != NULL) {
    strsep(&end, ":");
    token = end;
}
kfree(test);

Answer 1

You are passing a string literal and strsep() modifies it, it's undefined behavior, try like this

char test[] = "A:B:C:D";

you should not free(test) , not the one in this suggestion, and also not the one in your code.

You are free() ing test , which is worst, you should learn about pointers and dynamic memory before attempting to write c code, specially if it will be a kernel module.

If you want, the compiler may warn you about that, but you should help the compiler by declaring any pointer that will point to a string literal, as const , for example in your case

const char *test = "Whatever";

then the compiler will say something like the first parameter to strsep() discards const qualifier , which would probably not prevent it from compiling but will let you see that you did something wrong.