Date: Mon, 28 Feb 2000 17:04:43 -0800 From: Brooks Davis <brooks@one-eyed-alien.net> To: Brooks Davis <brooks@one-eyed-alien.net> Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: mprotect(2) won't make shared memory read-only Message-ID: <20000228170443.A16556@orion.ac.hmc.edu> In-Reply-To: <20000228125013.A25992@orion.ac.hmc.edu>; from brooks@one-eyed-alien.net on Mon, Feb 28, 2000 at 12:50:13PM -0800 References: <20000228125013.A25992@orion.ac.hmc.edu>
next in thread | previous in thread | raw e-mail | index | archive | help
On Mon, Feb 28, 2000 at 12:50:13PM -0800, Brooks Davis wrote:
> On a -current system as of a week or two ago (as well as a 3.3-RC and a
> 2.2.8-STABLE box) I've found that mprotect fails with with EACCES when
> trying to make a shared memory segment that was created user read/write
> read-only. It works find if I malloc the memory instead and making the
> shm segment write-only or inaccessible works fine as well. Is this
> expected behavior? If so it's pretty weird.
Following up on this. Charles Randall suggested I try shmctl to make
the segment read-only. Unfortunatly it appears that shared memory
premissions are screwed up as well. You can create a read-only shared
memory segment either via shmget or via shmctl on an existing read-write
segment and it will appear via ipcs, but it doesn't appear to have any
effect. The following program creates a read-only segment and then
proceds to write to it twice, both of which work under FreeBSD -current.
When run on a Solaris 2.6 machine it segfaults in the first write.
--<cut>--
/* Test read-only shared memory segments */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#define SIZE 1024*sizeof(int)
int main(int argc, char **argv)
{
int *array;
int shmid;
shmid = shmget(IPC_PRIVATE, SIZE, SHM_R);
array = shmat(shmid, NULL, 0);
bzero(array, SIZE);
fprintf(stderr, "array[0] = %d\n", array[0]);
array[0] = 1;
fprintf(stderr, "array[0] = %d\n", array[0]);
shmctl(shmid, IPC_RMID, NULL);
return 0;
}
--<cut>--
Thanks,
Brooks
--
Any statement of the form "X is the one, true Y" is FALSE.
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20000228170443.A16556>