Bug 104907

Filling up a disk using mmap(2) causes some kind of livelock.  The system becomes
unresponsive.  These messages appear on the console:

Oct 29 14:54:16 sonne kernel: pid 7 (pagedaemon), uid 0 inumber 131261 on /: filesystem full
vnode_pager_putpages: I/O error 28
vnode_pager_putpages: residual I/O 131072 at 44656
vnode_pager_putpages: I/O error 28
vnode_pager_putpages: residual I/O 131072 at 45689
vnode_pager_putpages: I/O error 28
vnode_pager_putpages: residual I/O 131072 at 45391

etc.

It's easy to reproduce by unpriviledged user, so it's kind of DoS bug.

How-To-Repeat: Make sure you have _not_ enough disk space and run the following program:

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/mman.h>

/*
 * if there is not enough space in the filesystem, this will crash freebsd.
 */

int main(void)
{
        int fd;
        int ret;
        char *addr;
        size_t len=1000000000L;
        char *path="big_file";
        int i;

        fd=open(path, O_RDWR | O_CREAT | O_EXCL, 0664);

        if (fd<0) {
                perror("open");
                exit(-1);
        }

        ret=ftruncate(fd, len);

        if (ret!=0) {
                perror("ftruncate");
                unlink(path);
                exit(-1);
        }

        addr=mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);

        if (addr==MAP_FAILED) {
                perror("mmap");
                unlink(path);
                exit(-1);
        }

        for (i=0; i<len; i++)
                *(addr+i)='\42';

        printf("somehow, it survived.\n");
        unlink(path);

        return 0;
}