Date: Fri, 3 Sep 2010 21:51:27 GMT From: Ion Gaztaņaga <igaztanaga@gmail.com> To: freebsd-gnats-submit@FreeBSD.org Subject: kern/150260: mmap fails with EPERM (not documented) if read-only shared memory is mmapped with MAP_PRIVATE & PROT_WRITE Message-ID: <201009032151.o83LpRd5018533@www.freebsd.org> Resent-Message-ID: <201009032200.o83M0Dth012526@freefall.freebsd.org>
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>Number: 150260
>Category: kern
>Synopsis: mmap fails with EPERM (not documented) if read-only shared memory is mmapped with MAP_PRIVATE & PROT_WRITE
>Confidential: no
>Severity: serious
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Fri Sep 03 22:00:13 UTC 2010
>Closed-Date:
>Last-Modified:
>Originator: Ion Gaztaņaga
>Release: 8.0-RELEASE-p2
>Organization:
>Environment:
FreeBSD pcbsd-4080 8.0-RELEASE-p2 FreeBSD 8.0-RELEASE-p2 #4: Thu Jan 7 09:20:42 PST 2010 root@build8x32.pcbsd.org:/usr/obj/usr/pcbsd-build80/fbsd-source/8.0-src/sys/PCBSD i386
>Description:
mmap allows copy on write file/shared memory mapping via MAP_PRIVATE and only requires a read-only file descriptor. This works with files but not with shared memory objects (mmap returns EPERM).
>How-To-Repeat:
Execute the attached c program
>Fix:
Patch attached with submission follows:
#include <sys/types.h>
#include <sys/mman.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
int main()
{
shm_unlink("/myshm");
int fd = shm_open("/myshm", O_CREAT | O_RDWR, 0644);
if(fd >= 0){
if(ftruncate(fd, 1000) < 0){
printf("Error truncating");
close(fd);
}
else{
close(fd);
fd = shm_open("/myshm", O_RDONLY/*O_RDWR*/, 0644);
if(fd >= 0){
void *addr = mmap(0, 1000, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (MAP_FAILED == addr){
printf("mmap failed, errno: %s", strerror(errno));
}
else{
printf("mmap OK");
munmap(addr, 1000);
}
close(fd);
}
else{
printf("Error opening shmem");
}
}
}
else{
printf("Error creating shmem");
}
shm_unlink("/myshm");
return 0;
}
>Release-Note:
>Audit-Trail:
>Unformatted:
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