Re: [9fans] segattach in telnetd

[arisawa <arisawa@ar.aichi-u.ac.jp>]

Hello cinap,

My experiment here.

void
main(int argc, char *argv[])
{	char *ap;
	char buf[1];
	ARGBEGIN{
	default: usage();
	}ARGEND
	
	ap = segattach(0,"share",0,1024);
	print("%p\n",ap);	// ffffffff  error

	/* compare */
	ap = sbrk(0);
	print("sbrk %p\n",ap);	// 6cb0
	ap += 2*1024*1024;
	print("%p\n",ap);	// 206cb0
	ap = segattach(0, "shared", ap, 1024);
	print("%p\n",ap);	// 206000

	read(0,buf,1);
}

we can find the allocated share memory:

term% cat /proc/612768/segment
Stack     defff000 dffff000    1
Text   R      1000     6000    1
Data          6000     7000    1
Bss           7000     7000    1
Shared      206000   207000    1
term% 

note that 0x206cb0 + 0x400 > 0x20700.
if we believe that we have a memory
of range [mp,mp+1024) by executing
mp = share(1024)
then we will fail.

Kenji Arisawa

2014/09/14 12:17、cinap_lenrek@felloff.net のメール：

> it should round va down and va+len up as neccesary
> to make them page aligned. but the initial passed
> range should be covered by the created segment
> in any case.