linked list within a kernel probe

[chrishell]

hello Billie, thank you for your support. As you can see I have 2 
different structures. The first one is defined for a global structure, 
which holds all information which I need within the kprobe (called 
kprobe_head). Then I have another structure (called kprobe_mem_cache), 
which is defined to be the structure the linked list is made of. So the 
head of the linked list is within a structure different of the struct 
the linked list is made of. I hope this is not a problem, but should not.
First I tried to initialize the head of the linked list. 
INIT_LIST_HEAD(pHead->p_mem_cache) but this lead to a crash already!

To remind:

struct kprobe_head {
     struct list_head       *p_mem_cache;
     struct kprobe_fsops    *pfops;
     struct kprobe          *pProbe;
};

and

pHead = (struct kprobe_head*) kzalloc(sizeof(struct kprobe_head), 
GFP_KERNEL);

(this is done in the _init function)

Then I tried it the way you saw in my first mail, with a struct on the 
stack. Which is wrong, but at least Im able to setup the list, and can 
traverse the list, even shortly after leaving the function, until the 
memory is used again. But I can see this is not a solution.

My question now is: which pointer has to be INIT_LIST_HEAD and when?

Thank you in advance

BR Christian



> 
>>
>> static __u8 _kprobe_setup_cache_elements( struct kprobe_head *pHead,
>> __u16 elements, __u32 size)
>> {
> …
>>       struct list_head local_head;
>>
>>       INIT_LIST_HEAD(&local_head);
>>
> …
>>           pHead->p_mem_cache = &local_head;
> …
>> }
> 
> just from a quick look at this code, my guess is that you should not be using stack addresses in your list.
> Your local_head is on the stack, therefore it gets corrupted after you exit your function and invoke other functions.
> Did you really mean to store a pointer to local_head, or was your intention to point to the first element on local_head?
> 
> 
> 
> 
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