mmap giving Permission Denied error

[Ravi Teja]

Hello all,

I have successfully acessed(read and write) to 0x00000000(NULL) address. I
had to make certain changes in .config file and recompile it.

Thank you all.

Regards
Ravi Teja


On Sat, Sep 21, 2013 at 8:00 PM, anish singh <anish198519851985 at gmail.com>wrote:

>
> 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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