linux/drivers/oprofile/oprofilefs.c
Eric W. Biederman 7f78e03513 fs: Limit sys_mount to only request filesystem modules.
Modify the request_module to prefix the file system type with "fs-"
and add aliases to all of the filesystems that can be built as modules
to match.

A common practice is to build all of the kernel code and leave code
that is not commonly needed as modules, with the result that many
users are exposed to any bug anywhere in the kernel.

Looking for filesystems with a fs- prefix limits the pool of possible
modules that can be loaded by mount to just filesystems trivially
making things safer with no real cost.

Using aliases means user space can control the policy of which
filesystem modules are auto-loaded by editing /etc/modprobe.d/*.conf
with blacklist and alias directives.  Allowing simple, safe,
well understood work-arounds to known problematic software.

This also addresses a rare but unfortunate problem where the filesystem
name is not the same as it's module name and module auto-loading
would not work.  While writing this patch I saw a handful of such
cases.  The most significant being autofs that lives in the module
autofs4.

This is relevant to user namespaces because we can reach the request
module in get_fs_type() without having any special permissions, and
people get uncomfortable when a user specified string (in this case
the filesystem type) goes all of the way to request_module.

After having looked at this issue I don't think there is any
particular reason to perform any filtering or permission checks beyond
making it clear in the module request that we want a filesystem
module.  The common pattern in the kernel is to call request_module()
without regards to the users permissions.  In general all a filesystem
module does once loaded is call register_filesystem() and go to sleep.
Which means there is not much attack surface exposed by loading a
filesytem module unless the filesystem is mounted.  In a user
namespace filesystems are not mounted unless .fs_flags = FS_USERNS_MOUNT,
which most filesystems do not set today.

Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Acked-by: Kees Cook <keescook@chromium.org>
Reported-by: Kees Cook <keescook@google.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
2013-03-03 19:36:31 -08:00

292 lines
6.7 KiB
C

/**
* @file oprofilefs.c
*
* @remark Copyright 2002 OProfile authors
* @remark Read the file COPYING
*
* @author John Levon
*
* A simple filesystem for configuration and
* access of oprofile.
*/
#include <linux/init.h>
#include <linux/module.h>
#include <linux/oprofile.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <asm/uaccess.h>
#include "oprof.h"
#define OPROFILEFS_MAGIC 0x6f70726f
DEFINE_RAW_SPINLOCK(oprofilefs_lock);
static struct inode *oprofilefs_get_inode(struct super_block *sb, int mode)
{
struct inode *inode = new_inode(sb);
if (inode) {
inode->i_ino = get_next_ino();
inode->i_mode = mode;
inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
}
return inode;
}
static const struct super_operations s_ops = {
.statfs = simple_statfs,
.drop_inode = generic_delete_inode,
};
ssize_t oprofilefs_str_to_user(char const *str, char __user *buf, size_t count, loff_t *offset)
{
return simple_read_from_buffer(buf, count, offset, str, strlen(str));
}
#define TMPBUFSIZE 50
ssize_t oprofilefs_ulong_to_user(unsigned long val, char __user *buf, size_t count, loff_t *offset)
{
char tmpbuf[TMPBUFSIZE];
size_t maxlen = snprintf(tmpbuf, TMPBUFSIZE, "%lu\n", val);
if (maxlen > TMPBUFSIZE)
maxlen = TMPBUFSIZE;
return simple_read_from_buffer(buf, count, offset, tmpbuf, maxlen);
}
/*
* Note: If oprofilefs_ulong_from_user() returns 0, then *val remains
* unchanged and might be uninitialized. This follows write syscall
* implementation when count is zero: "If count is zero ... [and if]
* no errors are detected, 0 will be returned without causing any
* other effect." (man 2 write)
*/
int oprofilefs_ulong_from_user(unsigned long *val, char const __user *buf, size_t count)
{
char tmpbuf[TMPBUFSIZE];
unsigned long flags;
if (!count)
return 0;
if (count > TMPBUFSIZE - 1)
return -EINVAL;
memset(tmpbuf, 0x0, TMPBUFSIZE);
if (copy_from_user(tmpbuf, buf, count))
return -EFAULT;
raw_spin_lock_irqsave(&oprofilefs_lock, flags);
*val = simple_strtoul(tmpbuf, NULL, 0);
raw_spin_unlock_irqrestore(&oprofilefs_lock, flags);
return count;
}
static ssize_t ulong_read_file(struct file *file, char __user *buf, size_t count, loff_t *offset)
{
unsigned long *val = file->private_data;
return oprofilefs_ulong_to_user(*val, buf, count, offset);
}
static ssize_t ulong_write_file(struct file *file, char const __user *buf, size_t count, loff_t *offset)
{
unsigned long value;
int retval;
if (*offset)
return -EINVAL;
retval = oprofilefs_ulong_from_user(&value, buf, count);
if (retval <= 0)
return retval;
retval = oprofile_set_ulong(file->private_data, value);
if (retval)
return retval;
return count;
}
static const struct file_operations ulong_fops = {
.read = ulong_read_file,
.write = ulong_write_file,
.open = simple_open,
.llseek = default_llseek,
};
static const struct file_operations ulong_ro_fops = {
.read = ulong_read_file,
.open = simple_open,
.llseek = default_llseek,
};
static int __oprofilefs_create_file(struct super_block *sb,
struct dentry *root, char const *name, const struct file_operations *fops,
int perm, void *priv)
{
struct dentry *dentry;
struct inode *inode;
mutex_lock(&root->d_inode->i_mutex);
dentry = d_alloc_name(root, name);
if (!dentry) {
mutex_unlock(&root->d_inode->i_mutex);
return -ENOMEM;
}
inode = oprofilefs_get_inode(sb, S_IFREG | perm);
if (!inode) {
dput(dentry);
mutex_unlock(&root->d_inode->i_mutex);
return -ENOMEM;
}
inode->i_fop = fops;
inode->i_private = priv;
d_add(dentry, inode);
mutex_unlock(&root->d_inode->i_mutex);
return 0;
}
int oprofilefs_create_ulong(struct super_block *sb, struct dentry *root,
char const *name, unsigned long *val)
{
return __oprofilefs_create_file(sb, root, name,
&ulong_fops, 0644, val);
}
int oprofilefs_create_ro_ulong(struct super_block *sb, struct dentry *root,
char const *name, unsigned long *val)
{
return __oprofilefs_create_file(sb, root, name,
&ulong_ro_fops, 0444, val);
}
static ssize_t atomic_read_file(struct file *file, char __user *buf, size_t count, loff_t *offset)
{
atomic_t *val = file->private_data;
return oprofilefs_ulong_to_user(atomic_read(val), buf, count, offset);
}
static const struct file_operations atomic_ro_fops = {
.read = atomic_read_file,
.open = simple_open,
.llseek = default_llseek,
};
int oprofilefs_create_ro_atomic(struct super_block *sb, struct dentry *root,
char const *name, atomic_t *val)
{
return __oprofilefs_create_file(sb, root, name,
&atomic_ro_fops, 0444, val);
}
int oprofilefs_create_file(struct super_block *sb, struct dentry *root,
char const *name, const struct file_operations *fops)
{
return __oprofilefs_create_file(sb, root, name, fops, 0644, NULL);
}
int oprofilefs_create_file_perm(struct super_block *sb, struct dentry *root,
char const *name, const struct file_operations *fops, int perm)
{
return __oprofilefs_create_file(sb, root, name, fops, perm, NULL);
}
struct dentry *oprofilefs_mkdir(struct super_block *sb,
struct dentry *root, char const *name)
{
struct dentry *dentry;
struct inode *inode;
mutex_lock(&root->d_inode->i_mutex);
dentry = d_alloc_name(root, name);
if (!dentry) {
mutex_unlock(&root->d_inode->i_mutex);
return NULL;
}
inode = oprofilefs_get_inode(sb, S_IFDIR | 0755);
if (!inode) {
dput(dentry);
mutex_unlock(&root->d_inode->i_mutex);
return NULL;
}
inode->i_op = &simple_dir_inode_operations;
inode->i_fop = &simple_dir_operations;
d_add(dentry, inode);
mutex_unlock(&root->d_inode->i_mutex);
return dentry;
}
static int oprofilefs_fill_super(struct super_block *sb, void *data, int silent)
{
struct inode *root_inode;
sb->s_blocksize = PAGE_CACHE_SIZE;
sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
sb->s_magic = OPROFILEFS_MAGIC;
sb->s_op = &s_ops;
sb->s_time_gran = 1;
root_inode = oprofilefs_get_inode(sb, S_IFDIR | 0755);
if (!root_inode)
return -ENOMEM;
root_inode->i_op = &simple_dir_inode_operations;
root_inode->i_fop = &simple_dir_operations;
sb->s_root = d_make_root(root_inode);
if (!sb->s_root)
return -ENOMEM;
oprofile_create_files(sb, sb->s_root);
// FIXME: verify kill_litter_super removes our dentries
return 0;
}
static struct dentry *oprofilefs_mount(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data)
{
return mount_single(fs_type, flags, data, oprofilefs_fill_super);
}
static struct file_system_type oprofilefs_type = {
.owner = THIS_MODULE,
.name = "oprofilefs",
.mount = oprofilefs_mount,
.kill_sb = kill_litter_super,
};
MODULE_ALIAS_FS("oprofilefs");
int __init oprofilefs_register(void)
{
return register_filesystem(&oprofilefs_type);
}
void __exit oprofilefs_unregister(void)
{
unregister_filesystem(&oprofilefs_type);
}