linux/fs/efs/super.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

364 lines
8.5 KiB
C

/*
* super.c
*
* Copyright (c) 1999 Al Smith
*
* Portions derived from work (c) 1995,1996 Christian Vogelgsang.
*/
#include <linux/init.h>
#include <linux/module.h>
#include <linux/exportfs.h>
#include <linux/slab.h>
#include <linux/buffer_head.h>
#include <linux/vfs.h>
#include "efs.h"
#include <linux/efs_vh.h>
#include <linux/efs_fs_sb.h>
static int efs_statfs(struct dentry *dentry, struct kstatfs *buf);
static int efs_fill_super(struct super_block *s, void *d, int silent);
static struct dentry *efs_mount(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data)
{
return mount_bdev(fs_type, flags, dev_name, data, efs_fill_super);
}
static struct file_system_type efs_fs_type = {
.owner = THIS_MODULE,
.name = "efs",
.mount = efs_mount,
.kill_sb = kill_block_super,
.fs_flags = FS_REQUIRES_DEV,
};
MODULE_ALIAS_FS("efs");
static struct pt_types sgi_pt_types[] = {
{0x00, "SGI vh"},
{0x01, "SGI trkrepl"},
{0x02, "SGI secrepl"},
{0x03, "SGI raw"},
{0x04, "SGI bsd"},
{SGI_SYSV, "SGI sysv"},
{0x06, "SGI vol"},
{SGI_EFS, "SGI efs"},
{0x08, "SGI lv"},
{0x09, "SGI rlv"},
{0x0A, "SGI xfs"},
{0x0B, "SGI xfslog"},
{0x0C, "SGI xlv"},
{0x82, "Linux swap"},
{0x83, "Linux native"},
{0, NULL}
};
static struct kmem_cache * efs_inode_cachep;
static struct inode *efs_alloc_inode(struct super_block *sb)
{
struct efs_inode_info *ei;
ei = (struct efs_inode_info *)kmem_cache_alloc(efs_inode_cachep, GFP_KERNEL);
if (!ei)
return NULL;
return &ei->vfs_inode;
}
static void efs_i_callback(struct rcu_head *head)
{
struct inode *inode = container_of(head, struct inode, i_rcu);
kmem_cache_free(efs_inode_cachep, INODE_INFO(inode));
}
static void efs_destroy_inode(struct inode *inode)
{
call_rcu(&inode->i_rcu, efs_i_callback);
}
static void init_once(void *foo)
{
struct efs_inode_info *ei = (struct efs_inode_info *) foo;
inode_init_once(&ei->vfs_inode);
}
static int init_inodecache(void)
{
efs_inode_cachep = kmem_cache_create("efs_inode_cache",
sizeof(struct efs_inode_info),
0, SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD,
init_once);
if (efs_inode_cachep == NULL)
return -ENOMEM;
return 0;
}
static void destroy_inodecache(void)
{
/*
* Make sure all delayed rcu free inodes are flushed before we
* destroy cache.
*/
rcu_barrier();
kmem_cache_destroy(efs_inode_cachep);
}
static void efs_put_super(struct super_block *s)
{
kfree(s->s_fs_info);
s->s_fs_info = NULL;
}
static int efs_remount(struct super_block *sb, int *flags, char *data)
{
*flags |= MS_RDONLY;
return 0;
}
static const struct super_operations efs_superblock_operations = {
.alloc_inode = efs_alloc_inode,
.destroy_inode = efs_destroy_inode,
.put_super = efs_put_super,
.statfs = efs_statfs,
.remount_fs = efs_remount,
};
static const struct export_operations efs_export_ops = {
.fh_to_dentry = efs_fh_to_dentry,
.fh_to_parent = efs_fh_to_parent,
.get_parent = efs_get_parent,
};
static int __init init_efs_fs(void) {
int err;
printk("EFS: "EFS_VERSION" - http://aeschi.ch.eu.org/efs/\n");
err = init_inodecache();
if (err)
goto out1;
err = register_filesystem(&efs_fs_type);
if (err)
goto out;
return 0;
out:
destroy_inodecache();
out1:
return err;
}
static void __exit exit_efs_fs(void) {
unregister_filesystem(&efs_fs_type);
destroy_inodecache();
}
module_init(init_efs_fs)
module_exit(exit_efs_fs)
static efs_block_t efs_validate_vh(struct volume_header *vh) {
int i;
__be32 cs, *ui;
int csum;
efs_block_t sblock = 0; /* shuts up gcc */
struct pt_types *pt_entry;
int pt_type, slice = -1;
if (be32_to_cpu(vh->vh_magic) != VHMAGIC) {
/*
* assume that we're dealing with a partition and allow
* read_super() to try and detect a valid superblock
* on the next block.
*/
return 0;
}
ui = ((__be32 *) (vh + 1)) - 1;
for(csum = 0; ui >= ((__be32 *) vh);) {
cs = *ui--;
csum += be32_to_cpu(cs);
}
if (csum) {
printk(KERN_INFO "EFS: SGI disklabel: checksum bad, label corrupted\n");
return 0;
}
#ifdef DEBUG
printk(KERN_DEBUG "EFS: bf: \"%16s\"\n", vh->vh_bootfile);
for(i = 0; i < NVDIR; i++) {
int j;
char name[VDNAMESIZE+1];
for(j = 0; j < VDNAMESIZE; j++) {
name[j] = vh->vh_vd[i].vd_name[j];
}
name[j] = (char) 0;
if (name[0]) {
printk(KERN_DEBUG "EFS: vh: %8s block: 0x%08x size: 0x%08x\n",
name,
(int) be32_to_cpu(vh->vh_vd[i].vd_lbn),
(int) be32_to_cpu(vh->vh_vd[i].vd_nbytes));
}
}
#endif
for(i = 0; i < NPARTAB; i++) {
pt_type = (int) be32_to_cpu(vh->vh_pt[i].pt_type);
for(pt_entry = sgi_pt_types; pt_entry->pt_name; pt_entry++) {
if (pt_type == pt_entry->pt_type) break;
}
#ifdef DEBUG
if (be32_to_cpu(vh->vh_pt[i].pt_nblks)) {
printk(KERN_DEBUG "EFS: pt %2d: start: %08d size: %08d type: 0x%02x (%s)\n",
i,
(int) be32_to_cpu(vh->vh_pt[i].pt_firstlbn),
(int) be32_to_cpu(vh->vh_pt[i].pt_nblks),
pt_type,
(pt_entry->pt_name) ? pt_entry->pt_name : "unknown");
}
#endif
if (IS_EFS(pt_type)) {
sblock = be32_to_cpu(vh->vh_pt[i].pt_firstlbn);
slice = i;
}
}
if (slice == -1) {
printk(KERN_NOTICE "EFS: partition table contained no EFS partitions\n");
#ifdef DEBUG
} else {
printk(KERN_INFO "EFS: using slice %d (type %s, offset 0x%x)\n",
slice,
(pt_entry->pt_name) ? pt_entry->pt_name : "unknown",
sblock);
#endif
}
return sblock;
}
static int efs_validate_super(struct efs_sb_info *sb, struct efs_super *super) {
if (!IS_EFS_MAGIC(be32_to_cpu(super->fs_magic)))
return -1;
sb->fs_magic = be32_to_cpu(super->fs_magic);
sb->total_blocks = be32_to_cpu(super->fs_size);
sb->first_block = be32_to_cpu(super->fs_firstcg);
sb->group_size = be32_to_cpu(super->fs_cgfsize);
sb->data_free = be32_to_cpu(super->fs_tfree);
sb->inode_free = be32_to_cpu(super->fs_tinode);
sb->inode_blocks = be16_to_cpu(super->fs_cgisize);
sb->total_groups = be16_to_cpu(super->fs_ncg);
return 0;
}
static int efs_fill_super(struct super_block *s, void *d, int silent)
{
struct efs_sb_info *sb;
struct buffer_head *bh;
struct inode *root;
int ret = -EINVAL;
sb = kzalloc(sizeof(struct efs_sb_info), GFP_KERNEL);
if (!sb)
return -ENOMEM;
s->s_fs_info = sb;
s->s_magic = EFS_SUPER_MAGIC;
if (!sb_set_blocksize(s, EFS_BLOCKSIZE)) {
printk(KERN_ERR "EFS: device does not support %d byte blocks\n",
EFS_BLOCKSIZE);
goto out_no_fs_ul;
}
/* read the vh (volume header) block */
bh = sb_bread(s, 0);
if (!bh) {
printk(KERN_ERR "EFS: cannot read volume header\n");
goto out_no_fs_ul;
}
/*
* if this returns zero then we didn't find any partition table.
* this isn't (yet) an error - just assume for the moment that
* the device is valid and go on to search for a superblock.
*/
sb->fs_start = efs_validate_vh((struct volume_header *) bh->b_data);
brelse(bh);
if (sb->fs_start == -1) {
goto out_no_fs_ul;
}
bh = sb_bread(s, sb->fs_start + EFS_SUPER);
if (!bh) {
printk(KERN_ERR "EFS: cannot read superblock\n");
goto out_no_fs_ul;
}
if (efs_validate_super(sb, (struct efs_super *) bh->b_data)) {
#ifdef DEBUG
printk(KERN_WARNING "EFS: invalid superblock at block %u\n", sb->fs_start + EFS_SUPER);
#endif
brelse(bh);
goto out_no_fs_ul;
}
brelse(bh);
if (!(s->s_flags & MS_RDONLY)) {
#ifdef DEBUG
printk(KERN_INFO "EFS: forcing read-only mode\n");
#endif
s->s_flags |= MS_RDONLY;
}
s->s_op = &efs_superblock_operations;
s->s_export_op = &efs_export_ops;
root = efs_iget(s, EFS_ROOTINODE);
if (IS_ERR(root)) {
printk(KERN_ERR "EFS: get root inode failed\n");
ret = PTR_ERR(root);
goto out_no_fs;
}
s->s_root = d_make_root(root);
if (!(s->s_root)) {
printk(KERN_ERR "EFS: get root dentry failed\n");
ret = -ENOMEM;
goto out_no_fs;
}
return 0;
out_no_fs_ul:
out_no_fs:
s->s_fs_info = NULL;
kfree(sb);
return ret;
}
static int efs_statfs(struct dentry *dentry, struct kstatfs *buf) {
struct super_block *sb = dentry->d_sb;
struct efs_sb_info *sbi = SUPER_INFO(sb);
u64 id = huge_encode_dev(sb->s_bdev->bd_dev);
buf->f_type = EFS_SUPER_MAGIC; /* efs magic number */
buf->f_bsize = EFS_BLOCKSIZE; /* blocksize */
buf->f_blocks = sbi->total_groups * /* total data blocks */
(sbi->group_size - sbi->inode_blocks);
buf->f_bfree = sbi->data_free; /* free data blocks */
buf->f_bavail = sbi->data_free; /* free blocks for non-root */
buf->f_files = sbi->total_groups * /* total inodes */
sbi->inode_blocks *
(EFS_BLOCKSIZE / sizeof(struct efs_dinode));
buf->f_ffree = sbi->inode_free; /* free inodes */
buf->f_fsid.val[0] = (u32)id;
buf->f_fsid.val[1] = (u32)(id >> 32);
buf->f_namelen = EFS_MAXNAMELEN; /* max filename length */
return 0;
}