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namespace.c
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namespace.c
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/*
* linux/fs/namespace.c
*
* (C) Copyright Al Viro 2000, 2001
* Released under GPL v2.
*
* Based on code from fs/super.c, copyright Linus Torvalds and others.
* Heavily rewritten.
*/
#include <linux/config.h>
#include <linux/syscalls.h>
#include <linux/slab.h>
#include <linux/sched.h>
#include <linux/smp_lock.h>
#include <linux/init.h>
#include <linux/quotaops.h>
#include <linux/acct.h>
#include <linux/module.h>
#include <linux/seq_file.h>
#include <linux/namespace.h>
#include <linux/namei.h>
#include <linux/security.h>
#include <linux/mount.h>
#include <asm/uaccess.h>
#include <asm/unistd.h>
extern int __init init_rootfs(void);
#ifdef CONFIG_SYSFS
extern int __init sysfs_init(void);
#else
static inline int sysfs_init(void)
{
return 0;
}
#endif
/* spinlock for vfsmount related operations, inplace of dcache_lock */
__cacheline_aligned_in_smp DEFINE_SPINLOCK(vfsmount_lock);
static struct list_head *mount_hashtable;
static int hash_mask __read_mostly, hash_bits __read_mostly;
static kmem_cache_t *mnt_cache;
static inline unsigned long hash(struct vfsmount *mnt, struct dentry *dentry)
{
unsigned long tmp = ((unsigned long) mnt / L1_CACHE_BYTES);
tmp += ((unsigned long) dentry / L1_CACHE_BYTES);
tmp = tmp + (tmp >> hash_bits);
return tmp & hash_mask;
}
struct vfsmount *alloc_vfsmnt(const char *name)
{
struct vfsmount *mnt = kmem_cache_alloc(mnt_cache, GFP_KERNEL);
if (mnt) {
memset(mnt, 0, sizeof(struct vfsmount));
atomic_set(&mnt->mnt_count,1);
INIT_LIST_HEAD(&mnt->mnt_hash);
INIT_LIST_HEAD(&mnt->mnt_child);
INIT_LIST_HEAD(&mnt->mnt_mounts);
INIT_LIST_HEAD(&mnt->mnt_list);
INIT_LIST_HEAD(&mnt->mnt_expire);
if (name) {
int size = strlen(name)+1;
char *newname = kmalloc(size, GFP_KERNEL);
if (newname) {
memcpy(newname, name, size);
mnt->mnt_devname = newname;
}
}
}
return mnt;
}
void free_vfsmnt(struct vfsmount *mnt)
{
kfree(mnt->mnt_devname);
kmem_cache_free(mnt_cache, mnt);
}
/*
* Now, lookup_mnt increments the ref count before returning
* the vfsmount struct.
*/
struct vfsmount *lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
{
struct list_head * head = mount_hashtable + hash(mnt, dentry);
struct list_head * tmp = head;
struct vfsmount *p, *found = NULL;
spin_lock(&vfsmount_lock);
for (;;) {
tmp = tmp->next;
p = NULL;
if (tmp == head)
break;
p = list_entry(tmp, struct vfsmount, mnt_hash);
if (p->mnt_parent == mnt && p->mnt_mountpoint == dentry) {
found = mntget(p);
break;
}
}
spin_unlock(&vfsmount_lock);
return found;
}
static inline int check_mnt(struct vfsmount *mnt)
{
return mnt->mnt_namespace == current->namespace;
}
static void detach_mnt(struct vfsmount *mnt, struct nameidata *old_nd)
{
old_nd->dentry = mnt->mnt_mountpoint;
old_nd->mnt = mnt->mnt_parent;
mnt->mnt_parent = mnt;
mnt->mnt_mountpoint = mnt->mnt_root;
list_del_init(&mnt->mnt_child);
list_del_init(&mnt->mnt_hash);
old_nd->dentry->d_mounted--;
}
static void attach_mnt(struct vfsmount *mnt, struct nameidata *nd)
{
mnt->mnt_parent = mntget(nd->mnt);
mnt->mnt_mountpoint = dget(nd->dentry);
list_add(&mnt->mnt_hash, mount_hashtable+hash(nd->mnt, nd->dentry));
list_add_tail(&mnt->mnt_child, &nd->mnt->mnt_mounts);
nd->dentry->d_mounted++;
}
static struct vfsmount *next_mnt(struct vfsmount *p, struct vfsmount *root)
{
struct list_head *next = p->mnt_mounts.next;
if (next == &p->mnt_mounts) {
while (1) {
if (p == root)
return NULL;
next = p->mnt_child.next;
if (next != &p->mnt_parent->mnt_mounts)
break;
p = p->mnt_parent;
}
}
return list_entry(next, struct vfsmount, mnt_child);
}
static struct vfsmount *
clone_mnt(struct vfsmount *old, struct dentry *root)
{
struct super_block *sb = old->mnt_sb;
struct vfsmount *mnt = alloc_vfsmnt(old->mnt_devname);
if (mnt) {
mnt->mnt_flags = old->mnt_flags;
atomic_inc(&sb->s_active);
mnt->mnt_sb = sb;
mnt->mnt_root = dget(root);
mnt->mnt_mountpoint = mnt->mnt_root;
mnt->mnt_parent = mnt;
mnt->mnt_namespace = current->namespace;
/* stick the duplicate mount on the same expiry list
* as the original if that was on one */
spin_lock(&vfsmount_lock);
if (!list_empty(&old->mnt_expire))
list_add(&mnt->mnt_expire, &old->mnt_expire);
spin_unlock(&vfsmount_lock);
}
return mnt;
}
void __mntput(struct vfsmount *mnt)
{
struct super_block *sb = mnt->mnt_sb;
dput(mnt->mnt_root);
free_vfsmnt(mnt);
deactivate_super(sb);
}
EXPORT_SYMBOL(__mntput);
/* iterator */
static void *m_start(struct seq_file *m, loff_t *pos)
{
struct namespace *n = m->private;
struct list_head *p;
loff_t l = *pos;
down_read(&n->sem);
list_for_each(p, &n->list)
if (!l--)
return list_entry(p, struct vfsmount, mnt_list);
return NULL;
}
static void *m_next(struct seq_file *m, void *v, loff_t *pos)
{
struct namespace *n = m->private;
struct list_head *p = ((struct vfsmount *)v)->mnt_list.next;
(*pos)++;
return p==&n->list ? NULL : list_entry(p, struct vfsmount, mnt_list);
}
static void m_stop(struct seq_file *m, void *v)
{
struct namespace *n = m->private;
up_read(&n->sem);
}
static inline void mangle(struct seq_file *m, const char *s)
{
seq_escape(m, s, " \t\n\\");
}
static int show_vfsmnt(struct seq_file *m, void *v)
{
struct vfsmount *mnt = v;
int err = 0;
static struct proc_fs_info {
int flag;
char *str;
} fs_info[] = {
{ MS_SYNCHRONOUS, ",sync" },
{ MS_DIRSYNC, ",dirsync" },
{ MS_MANDLOCK, ",mand" },
{ MS_NOATIME, ",noatime" },
{ MS_NODIRATIME, ",nodiratime" },
{ 0, NULL }
};
static struct proc_fs_info mnt_info[] = {
{ MNT_NOSUID, ",nosuid" },
{ MNT_NODEV, ",nodev" },
{ MNT_NOEXEC, ",noexec" },
{ 0, NULL }
};
struct proc_fs_info *fs_infop;
mangle(m, mnt->mnt_devname ? mnt->mnt_devname : "none");
seq_putc(m, ' ');
seq_path(m, mnt, mnt->mnt_root, " \t\n\\");
seq_putc(m, ' ');
mangle(m, mnt->mnt_sb->s_type->name);
seq_puts(m, mnt->mnt_sb->s_flags & MS_RDONLY ? " ro" : " rw");
for (fs_infop = fs_info; fs_infop->flag; fs_infop++) {
if (mnt->mnt_sb->s_flags & fs_infop->flag)
seq_puts(m, fs_infop->str);
}
for (fs_infop = mnt_info; fs_infop->flag; fs_infop++) {
if (mnt->mnt_flags & fs_infop->flag)
seq_puts(m, fs_infop->str);
}
if (mnt->mnt_sb->s_op->show_options)
err = mnt->mnt_sb->s_op->show_options(m, mnt);
seq_puts(m, " 0 0\n");
return err;
}
struct seq_operations mounts_op = {
.start = m_start,
.next = m_next,
.stop = m_stop,
.show = show_vfsmnt
};
/**
* may_umount_tree - check if a mount tree is busy
* @mnt: root of mount tree
*
* This is called to check if a tree of mounts has any
* open files, pwds, chroots or sub mounts that are
* busy.
*/
int may_umount_tree(struct vfsmount *mnt)
{
struct list_head *next;
struct vfsmount *this_parent = mnt;
int actual_refs;
int minimum_refs;
spin_lock(&vfsmount_lock);
actual_refs = atomic_read(&mnt->mnt_count);
minimum_refs = 2;
repeat:
next = this_parent->mnt_mounts.next;
resume:
while (next != &this_parent->mnt_mounts) {
struct vfsmount *p = list_entry(next, struct vfsmount, mnt_child);
next = next->next;
actual_refs += atomic_read(&p->mnt_count);
minimum_refs += 2;
if (!list_empty(&p->mnt_mounts)) {
this_parent = p;
goto repeat;
}
}
if (this_parent != mnt) {
next = this_parent->mnt_child.next;
this_parent = this_parent->mnt_parent;
goto resume;
}
spin_unlock(&vfsmount_lock);
if (actual_refs > minimum_refs)
return -EBUSY;
return 0;
}
EXPORT_SYMBOL(may_umount_tree);
/**
* may_umount - check if a mount point is busy
* @mnt: root of mount
*
* This is called to check if a mount point has any
* open files, pwds, chroots or sub mounts. If the
* mount has sub mounts this will return busy
* regardless of whether the sub mounts are busy.
*
* Doesn't take quota and stuff into account. IOW, in some cases it will
* give false negatives. The main reason why it's here is that we need
* a non-destructive way to look for easily umountable filesystems.
*/
int may_umount(struct vfsmount *mnt)
{
if (atomic_read(&mnt->mnt_count) > 2)
return -EBUSY;
return 0;
}
EXPORT_SYMBOL(may_umount);
static void umount_tree(struct vfsmount *mnt)
{
struct vfsmount *p;
LIST_HEAD(kill);
for (p = mnt; p; p = next_mnt(p, mnt)) {
list_del(&p->mnt_list);
list_add(&p->mnt_list, &kill);
p->mnt_namespace = NULL;
}
while (!list_empty(&kill)) {
mnt = list_entry(kill.next, struct vfsmount, mnt_list);
list_del_init(&mnt->mnt_list);
list_del_init(&mnt->mnt_expire);
if (mnt->mnt_parent == mnt) {
spin_unlock(&vfsmount_lock);
} else {
struct nameidata old_nd;
detach_mnt(mnt, &old_nd);
spin_unlock(&vfsmount_lock);
path_release(&old_nd);
}
mntput(mnt);
spin_lock(&vfsmount_lock);
}
}
static int do_umount(struct vfsmount *mnt, int flags)
{
struct super_block * sb = mnt->mnt_sb;
int retval;
retval = security_sb_umount(mnt, flags);
if (retval)
return retval;
/*
* Allow userspace to request a mountpoint be expired rather than
* unmounting unconditionally. Unmount only happens if:
* (1) the mark is already set (the mark is cleared by mntput())
* (2) the usage count == 1 [parent vfsmount] + 1 [sys_umount]
*/
if (flags & MNT_EXPIRE) {
if (mnt == current->fs->rootmnt ||
flags & (MNT_FORCE | MNT_DETACH))
return -EINVAL;
if (atomic_read(&mnt->mnt_count) != 2)
return -EBUSY;
if (!xchg(&mnt->mnt_expiry_mark, 1))
return -EAGAIN;
}
/*
* If we may have to abort operations to get out of this
* mount, and they will themselves hold resources we must
* allow the fs to do things. In the Unix tradition of
* 'Gee thats tricky lets do it in userspace' the umount_begin
* might fail to complete on the first run through as other tasks
* must return, and the like. Thats for the mount program to worry
* about for the moment.
*/
lock_kernel();
if( (flags&MNT_FORCE) && sb->s_op->umount_begin)
sb->s_op->umount_begin(sb);
unlock_kernel();
/*
* No sense to grab the lock for this test, but test itself looks
* somewhat bogus. Suggestions for better replacement?
* Ho-hum... In principle, we might treat that as umount + switch
* to rootfs. GC would eventually take care of the old vfsmount.
* Actually it makes sense, especially if rootfs would contain a
* /reboot - static binary that would close all descriptors and
* call reboot(9). Then init(8) could umount root and exec /reboot.
*/
if (mnt == current->fs->rootmnt && !(flags & MNT_DETACH)) {
/*
* Special case for "unmounting" root ...
* we just try to remount it readonly.
*/
down_write(&sb->s_umount);
if (!(sb->s_flags & MS_RDONLY)) {
lock_kernel();
DQUOT_OFF(sb);
retval = do_remount_sb(sb, MS_RDONLY, NULL, 0);
unlock_kernel();
}
up_write(&sb->s_umount);
return retval;
}
down_write(¤t->namespace->sem);
spin_lock(&vfsmount_lock);
if (atomic_read(&sb->s_active) == 1) {
/* last instance - try to be smart */
spin_unlock(&vfsmount_lock);
lock_kernel();
DQUOT_OFF(sb);
acct_auto_close(sb);
unlock_kernel();
security_sb_umount_close(mnt);
spin_lock(&vfsmount_lock);
}
retval = -EBUSY;
if (atomic_read(&mnt->mnt_count) == 2 || flags & MNT_DETACH) {
if (!list_empty(&mnt->mnt_list))
umount_tree(mnt);
retval = 0;
}
spin_unlock(&vfsmount_lock);
if (retval)
security_sb_umount_busy(mnt);
up_write(¤t->namespace->sem);
return retval;
}
/*
* Now umount can handle mount points as well as block devices.
* This is important for filesystems which use unnamed block devices.
*
* We now support a flag for forced unmount like the other 'big iron'
* unixes. Our API is identical to OSF/1 to avoid making a mess of AMD
*/
asmlinkage long sys_umount(char __user * name, int flags)
{
struct nameidata nd;
int retval;
retval = __user_walk(name, LOOKUP_FOLLOW, &nd);
if (retval)
goto out;
retval = -EINVAL;
if (nd.dentry != nd.mnt->mnt_root)
goto dput_and_out;
if (!check_mnt(nd.mnt))
goto dput_and_out;
retval = -EPERM;
if (!capable(CAP_SYS_ADMIN))
goto dput_and_out;
retval = do_umount(nd.mnt, flags);
dput_and_out:
path_release_on_umount(&nd);
out:
return retval;
}
#ifdef __ARCH_WANT_SYS_OLDUMOUNT
/*
* The 2.0 compatible umount. No flags.
*/
asmlinkage long sys_oldumount(char __user * name)
{
return sys_umount(name,0);
}
#endif
static int mount_is_safe(struct nameidata *nd)
{
if (capable(CAP_SYS_ADMIN))
return 0;
return -EPERM;
#ifdef notyet
if (S_ISLNK(nd->dentry->d_inode->i_mode))
return -EPERM;
if (nd->dentry->d_inode->i_mode & S_ISVTX) {
if (current->uid != nd->dentry->d_inode->i_uid)
return -EPERM;
}
if (permission(nd->dentry->d_inode, MAY_WRITE, nd))
return -EPERM;
return 0;
#endif
}
static int
lives_below_in_same_fs(struct dentry *d, struct dentry *dentry)
{
while (1) {
if (d == dentry)
return 1;
if (d == NULL || d == d->d_parent)
return 0;
d = d->d_parent;
}
}
static struct vfsmount *copy_tree(struct vfsmount *mnt, struct dentry *dentry)
{
struct vfsmount *res, *p, *q, *r, *s;
struct list_head *h;
struct nameidata nd;
res = q = clone_mnt(mnt, dentry);
if (!q)
goto Enomem;
q->mnt_mountpoint = mnt->mnt_mountpoint;
p = mnt;
for (h = mnt->mnt_mounts.next; h != &mnt->mnt_mounts; h = h->next) {
r = list_entry(h, struct vfsmount, mnt_child);
if (!lives_below_in_same_fs(r->mnt_mountpoint, dentry))
continue;
for (s = r; s; s = next_mnt(s, r)) {
while (p != s->mnt_parent) {
p = p->mnt_parent;
q = q->mnt_parent;
}
p = s;
nd.mnt = q;
nd.dentry = p->mnt_mountpoint;
q = clone_mnt(p, p->mnt_root);
if (!q)
goto Enomem;
spin_lock(&vfsmount_lock);
list_add_tail(&q->mnt_list, &res->mnt_list);
attach_mnt(q, &nd);
spin_unlock(&vfsmount_lock);
}
}
return res;
Enomem:
if (res) {
spin_lock(&vfsmount_lock);
umount_tree(res);
spin_unlock(&vfsmount_lock);
}
return NULL;
}
static int graft_tree(struct vfsmount *mnt, struct nameidata *nd)
{
int err;
if (mnt->mnt_sb->s_flags & MS_NOUSER)
return -EINVAL;
if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
S_ISDIR(mnt->mnt_root->d_inode->i_mode))
return -ENOTDIR;
err = -ENOENT;
down(&nd->dentry->d_inode->i_sem);
if (IS_DEADDIR(nd->dentry->d_inode))
goto out_unlock;
err = security_sb_check_sb(mnt, nd);
if (err)
goto out_unlock;
err = -ENOENT;
spin_lock(&vfsmount_lock);
if (IS_ROOT(nd->dentry) || !d_unhashed(nd->dentry)) {
struct list_head head;
attach_mnt(mnt, nd);
list_add_tail(&head, &mnt->mnt_list);
list_splice(&head, current->namespace->list.prev);
mntget(mnt);
err = 0;
}
spin_unlock(&vfsmount_lock);
out_unlock:
up(&nd->dentry->d_inode->i_sem);
if (!err)
security_sb_post_addmount(mnt, nd);
return err;
}
/*
* do loopback mount.
*/
static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
{
struct nameidata old_nd;
struct vfsmount *mnt = NULL;
int err = mount_is_safe(nd);
if (err)
return err;
if (!old_name || !*old_name)
return -EINVAL;
err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
if (err)
return err;
down_write(¤t->namespace->sem);
err = -EINVAL;
if (check_mnt(nd->mnt) && (!recurse || check_mnt(old_nd.mnt))) {
err = -ENOMEM;
if (recurse)
mnt = copy_tree(old_nd.mnt, old_nd.dentry);
else
mnt = clone_mnt(old_nd.mnt, old_nd.dentry);
}
if (mnt) {
/* stop bind mounts from expiring */
spin_lock(&vfsmount_lock);
list_del_init(&mnt->mnt_expire);
spin_unlock(&vfsmount_lock);
err = graft_tree(mnt, nd);
if (err) {
spin_lock(&vfsmount_lock);
umount_tree(mnt);
spin_unlock(&vfsmount_lock);
} else
mntput(mnt);
}
up_write(¤t->namespace->sem);
path_release(&old_nd);
return err;
}
/*
* change filesystem flags. dir should be a physical root of filesystem.
* If you've mounted a non-root directory somewhere and want to do remount
* on it - tough luck.
*/
static int do_remount(struct nameidata *nd, int flags, int mnt_flags,
void *data)
{
int err;
struct super_block * sb = nd->mnt->mnt_sb;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
if (!check_mnt(nd->mnt))
return -EINVAL;
if (nd->dentry != nd->mnt->mnt_root)
return -EINVAL;
down_write(&sb->s_umount);
err = do_remount_sb(sb, flags, data, 0);
if (!err)
nd->mnt->mnt_flags=mnt_flags;
up_write(&sb->s_umount);
if (!err)
security_sb_post_remount(nd->mnt, flags, data);
return err;
}
static int do_move_mount(struct nameidata *nd, char *old_name)
{
struct nameidata old_nd, parent_nd;
struct vfsmount *p;
int err = 0;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
if (!old_name || !*old_name)
return -EINVAL;
err = path_lookup(old_name, LOOKUP_FOLLOW, &old_nd);
if (err)
return err;
down_write(¤t->namespace->sem);
while(d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
;
err = -EINVAL;
if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
goto out;
err = -ENOENT;
down(&nd->dentry->d_inode->i_sem);
if (IS_DEADDIR(nd->dentry->d_inode))
goto out1;
spin_lock(&vfsmount_lock);
if (!IS_ROOT(nd->dentry) && d_unhashed(nd->dentry))
goto out2;
err = -EINVAL;
if (old_nd.dentry != old_nd.mnt->mnt_root)
goto out2;
if (old_nd.mnt == old_nd.mnt->mnt_parent)
goto out2;
if (S_ISDIR(nd->dentry->d_inode->i_mode) !=
S_ISDIR(old_nd.dentry->d_inode->i_mode))
goto out2;
err = -ELOOP;
for (p = nd->mnt; p->mnt_parent!=p; p = p->mnt_parent)
if (p == old_nd.mnt)
goto out2;
err = 0;
detach_mnt(old_nd.mnt, &parent_nd);
attach_mnt(old_nd.mnt, nd);
/* if the mount is moved, it should no longer be expire
* automatically */
list_del_init(&old_nd.mnt->mnt_expire);
out2:
spin_unlock(&vfsmount_lock);
out1:
up(&nd->dentry->d_inode->i_sem);
out:
up_write(¤t->namespace->sem);
if (!err)
path_release(&parent_nd);
path_release(&old_nd);
return err;
}
/*
* create a new mount for userspace and request it to be added into the
* namespace's tree
*/
static int do_new_mount(struct nameidata *nd, char *type, int flags,
int mnt_flags, char *name, void *data)
{
struct vfsmount *mnt;
if (!type || !memchr(type, 0, PAGE_SIZE))
return -EINVAL;
/* we need capabilities... */
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
mnt = do_kern_mount(type, flags, name, data);
if (IS_ERR(mnt))
return PTR_ERR(mnt);
return do_add_mount(mnt, nd, mnt_flags, NULL);
}
/*
* add a mount into a namespace's mount tree
* - provide the option of adding the new mount to an expiration list
*/
int do_add_mount(struct vfsmount *newmnt, struct nameidata *nd,
int mnt_flags, struct list_head *fslist)
{
int err;
down_write(¤t->namespace->sem);
/* Something was mounted here while we slept */
while(d_mountpoint(nd->dentry) && follow_down(&nd->mnt, &nd->dentry))
;
err = -EINVAL;
if (!check_mnt(nd->mnt))
goto unlock;
/* Refuse the same filesystem on the same mount point */
err = -EBUSY;
if (nd->mnt->mnt_sb == newmnt->mnt_sb &&
nd->mnt->mnt_root == nd->dentry)
goto unlock;
err = -EINVAL;
if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
goto unlock;
newmnt->mnt_flags = mnt_flags;
newmnt->mnt_namespace = current->namespace;
err = graft_tree(newmnt, nd);
if (err == 0 && fslist) {
/* add to the specified expiration list */
spin_lock(&vfsmount_lock);
list_add_tail(&newmnt->mnt_expire, fslist);
spin_unlock(&vfsmount_lock);
}
unlock:
up_write(¤t->namespace->sem);
mntput(newmnt);
return err;
}
EXPORT_SYMBOL_GPL(do_add_mount);
static void expire_mount(struct vfsmount *mnt, struct list_head *mounts)
{
spin_lock(&vfsmount_lock);
/*
* Check if mount is still attached, if not, let whoever holds it deal
* with the sucker
*/
if (mnt->mnt_parent == mnt) {
spin_unlock(&vfsmount_lock);
return;
}
/*
* Check that it is still dead: the count should now be 2 - as
* contributed by the vfsmount parent and the mntget above
*/
if (atomic_read(&mnt->mnt_count) == 2) {
struct nameidata old_nd;
/* delete from the namespace */
list_del_init(&mnt->mnt_list);
mnt->mnt_namespace = NULL;
detach_mnt(mnt, &old_nd);
spin_unlock(&vfsmount_lock);
path_release(&old_nd);
/*
* Now lay it to rest if this was the last ref on the superblock
*/
if (atomic_read(&mnt->mnt_sb->s_active) == 1) {
/* last instance - try to be smart */
lock_kernel();
DQUOT_OFF(mnt->mnt_sb);
acct_auto_close(mnt->mnt_sb);
unlock_kernel();
}
mntput(mnt);
} else {
/*
* Someone brought it back to life whilst we didn't have any
* locks held so return it to the expiration list
*/
list_add_tail(&mnt->mnt_expire, mounts);
spin_unlock(&vfsmount_lock);
}
}
/*
* process a list of expirable mountpoints with the intent of discarding any
* mountpoints that aren't in use and haven't been touched since last we came
* here
*/
void mark_mounts_for_expiry(struct list_head *mounts)
{
struct namespace *namespace;
struct vfsmount *mnt, *next;
LIST_HEAD(graveyard);
if (list_empty(mounts))
return;
spin_lock(&vfsmount_lock);
/* extract from the expiration list every vfsmount that matches the
* following criteria:
* - only referenced by its parent vfsmount
* - still marked for expiry (marked on the last call here; marks are
* cleared by mntput())
*/
list_for_each_entry_safe(mnt, next, mounts, mnt_expire) {
if (!xchg(&mnt->mnt_expiry_mark, 1) ||
atomic_read(&mnt->mnt_count) != 1)
continue;
mntget(mnt);
list_move(&mnt->mnt_expire, &graveyard);
}
/*
* go through the vfsmounts we've just consigned to the graveyard to
* - check that they're still dead
* - delete the vfsmount from the appropriate namespace under lock
* - dispose of the corpse
*/
while (!list_empty(&graveyard)) {
mnt = list_entry(graveyard.next, struct vfsmount, mnt_expire);
list_del_init(&mnt->mnt_expire);
/* don't do anything if the namespace is dead - all the
* vfsmounts from it are going away anyway */
namespace = mnt->mnt_namespace;
if (!namespace || !namespace->root)
continue;
get_namespace(namespace);
spin_unlock(&vfsmount_lock);
down_write(&namespace->sem);
expire_mount(mnt, mounts);
up_write(&namespace->sem);
mntput(mnt);
put_namespace(namespace);
spin_lock(&vfsmount_lock);
}
spin_unlock(&vfsmount_lock);
}
EXPORT_SYMBOL_GPL(mark_mounts_for_expiry);
/*
* Some copy_from_user() implementations do not return the exact number of
* bytes remaining to copy on a fault. But copy_mount_options() requires that.
* Note that this function differs from copy_from_user() in that it will oops
* on bad values of `to', rather than returning a short copy.
*/
static long
exact_copy_from_user(void *to, const void __user *from, unsigned long n)
{
char *t = to;
const char __user *f = from;
char c;
if (!access_ok(VERIFY_READ, from, n))
return n;
while (n) {
if (__get_user(c, f)) {
memset(t, 0, n);
break;
}
*t++ = c;
f++;
n--;
}
return n;
}
int copy_mount_options(const void __user *data, unsigned long *where)
{
int i;
unsigned long page;
unsigned long size;
*where = 0;
if (!data)
return 0;
if (!(page = __get_free_page(GFP_KERNEL)))
return -ENOMEM;
/* We only care that *some* data at the address the user
* gave us is valid. Just in case, we'll zero
* the remainder of the page.
*/
/* copy_from_user cannot cross TASK_SIZE ! */
size = TASK_SIZE - (unsigned long)data;
if (size > PAGE_SIZE)
size = PAGE_SIZE;
i = size - exact_copy_from_user((void *)page, data, size);
if (!i) {
free_page(page);
return -EFAULT;
}
if (i != PAGE_SIZE)
memset((char *)page + i, 0, PAGE_SIZE - i);
*where = page;
return 0;
}