Not sure for all the tasks slab is created initailly with contiguous memory. Slab cache
is shrinked when the system is low on memory.
If the memory is contiguous wriring few bytes after the kernel stack may corrupt a task_struct
of other task and it may for eg. corrupt the linked list element resuling in a crash. If it is not
contiguous, then it may corrupt some other data. If the data is crucial like link or based on
the value some decision is taken then it will crash. If some statistics field is overwritten
it may not impact the system stability.
On Thu, Sep 13, 2012 at 12:42 PM, shubham sharma <shubham20006@xxxxxxxxx> wrote:
Hi,
I did a quick calculation on this. The number of slab objects
On Thu, Sep 13, 2012 at 12:29 PM, Kshemendra KP
<kshemendra@xxxxxxxxxxxxx> wrote:
>
> In user space when you write beyond your address space (if your write
> crosses
> the page boundary alloacted to you), then process is terminated. In the
> kernel
> you are still writinng inside the kernel address space. Your write is not
> beyond
> kernel address space.
>
> Secondly you are corrupting some other data structure. The kernel stack is
> part
> of task_struct of the running process, a kmalloc or slab allocator might
> have
> provided this memory (task_-struct). When you write beyond this if the
> write modiefies some crucial data structure that may result in hang or a
> crash.
allocated for task_struct in my system are 280 and each size of each
object is 3264
---8<---
root@shubh-VirtualBox:~# cat /proc/slabinfo | grep task_struct
task_struct 262 280 3264 10 8 : tunables 0 0
0 : slabdata 28 28 0
---8<---
So if my understanding is correct, in case if i define an array of
more than 280*3264 bytes then it will corrupt the task_struct of at
least one significantly important process or at least the task_struct
of the process for my terminal will get corrupted?
>
>
>
>
> On Thu, Sep 13, 2012 at 12:15 PM, shubham sharma <shubham20006@xxxxxxxxx>
> wrote:
>>
>> Hi,
>>
>> As far as i know, the size of stack allocated in the kernel space is
>> 8Kb for each process. But in case i use more than 8Kb of memory from
>> the stack then what will happen? I think that in that case the system
>> would crash because i am accessing an illegal memory area. I wrote
>> kernel module in which i defined an integer array whose size was 8000.
>> But still it did not crash my system. Why?
>>
>> The module i wrote was as follows:
>>
>> #include <linux/kernel.h>
>> #include <linux/module.h>
>>
>> int __init init_my_module(void)
>> {
>> int arr[8000];
>> printk("%s:%d\tmodule initilized\n", __func__, __LINE__);
>> arr[1] = 1;
>> arr[4000] = 1;
>> arr[7999] = 1;
>> printk("%s:%d\tarr[1]:%d, arr[4000]:%d, arr[7999]:%d\n", __func__,
>> __LINE__, arr[1], arr[4000], arr[7999]);
>> return 0;
>> }
>>
>> void __exit cleanup_my_module(void)
>> {
>> printk("exiting\n");
>> return;
>> }
>>
>> module_init(init_my_module);
>> module_exit(cleanup_my_module);
>>
>> MODULE_LICENSE("GPL");
>>
>> _______________________________________________
>> Kernelnewbies mailing list
>> Kernelnewbies@xxxxxxxxxxxxxxxxx
>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>
_______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
