mmap giving Permission Denied error

[anish singh]

On Sep 21, 2013 7:35 PM, "Ravi Teja" <ravi2j at gmail.com> wrote:
>
> Hello Ratheesh,
>
> I have intentionally used MAP_FIXED flag as I am interested in mapping to
0x00000000.
AFAICS in linux generally mapping to null address is not allowed as this
decision helps in debugging null dereference errors.
>
> Even after setting the mmap_min_addr in /proc/sys/vm to 0 (which was
previously 4096), I am getting this error.
>
> Is there anything wrong that I am doing?
>
>
> On Sat, Sep 21, 2013 at 7:17 PM, ratheesh kannoth <ratheesh.ksz at gmail.com>
wrote:
>>
>> MAP_FIXED could be trying to get a map from  0.
>>
>>
>> Pls remove this flag and try.
>>
>>
>> On Sat, Sep 21, 2013 at 6:55 PM, Ravi Teja <ravi2j at gmail.com> wrote:
>>>
>>> Hello all,
>>>
>>> I tried mmap'ing to address zero after setting
/proc/sys/vm/mmap_min_addr to 0, but mmap is giving Permission Denied error.
>>>
>>> My C code is as below -
>>>
>>> #include <stdio.h>
>>> #include <stdlib.h>
>>> #include <sys/mman.h>
>>>
>>> int main(void)
>>> {
>>> int *ptr = NULL;
>>> ptr =
mmap(0,4096,PROT_READ|PROT_WRITE,MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED,-1,0);
>>> if(ptr == MAP_FAILED)
>>> {
>>> perror("Error in mapping\n");
>>> exit(1);
>>> }
>>> printf("After mmap\n");
>>> *ptr = 16;
>>> printf("Contents of address 0x%x is :: %d\n",ptr,*ptr);
>>> return 0;
>>> }
>>>
>>> Am I doing anything wrong here?
>>>
>>> Thank you in advance.
>>>
>>> Regards,
>>> Ravi Teja
>>>
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>>>
>>
>
>
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