fs_struct.c
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#include <linux/export.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/path.h>
#include <linux/slab.h>
#include <linux/fs_struct.h>
#include "internal.h"
/*
* Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
* It can block.
*/
void set_fs_root(struct fs_struct *fs, const struct path *path)
{
struct path old_root;
path_get(path);
spin_lock(&fs->lock);
write_seqcount_begin(&fs->seq);
old_root = fs->root;
fs->root = *path;
write_seqcount_end(&fs->seq);
spin_unlock(&fs->lock);
if (old_root.dentry)
path_put(&old_root);
}
/*
* Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
* It can block.
*/
void set_fs_pwd(struct fs_struct *fs, const struct path *path)
{
struct path old_pwd;
path_get(path);
spin_lock(&fs->lock);
write_seqcount_begin(&fs->seq);
old_pwd = fs->pwd;
fs->pwd = *path;
write_seqcount_end(&fs->seq);
spin_unlock(&fs->lock);
if (old_pwd.dentry)
path_put(&old_pwd);
}
static inline int replace_path(struct path *p, const struct path *old, const struct path *new)
{
if (likely(p->dentry != old->dentry || p->mnt != old->mnt))
return 0;
*p = *new;
return 1;
}
void chroot_fs_refs(const struct path *old_root, const struct path *new_root)
{
struct task_struct *g, *p;
struct fs_struct *fs;
int count = 0;
read_lock(&tasklist_lock);
do_each_thread(g, p) {
task_lock(p);
fs = p->fs;
if (fs) {
int hits = 0;
spin_lock(&fs->lock);
write_seqcount_begin(&fs->seq);
hits += replace_path(&fs->root, old_root, new_root);
hits += replace_path(&fs->pwd, old_root, new_root);
write_seqcount_end(&fs->seq);
while (hits--) {
count++;
path_get(new_root);
}
spin_unlock(&fs->lock);
}
task_unlock(p);
} while_each_thread(g, p);
read_unlock(&tasklist_lock);
while (count--)
path_put(old_root);
}
void free_fs_struct(struct fs_struct *fs)
{
path_put(&fs->root);
path_put(&fs->pwd);
kmem_cache_free(fs_cachep, fs);
}
void exit_fs(struct task_struct *tsk)
{
struct fs_struct *fs = tsk->fs;
if (fs) {
int kill;
task_lock(tsk);
spin_lock(&fs->lock);
tsk->fs = NULL;
kill = !--fs->users;
spin_unlock(&fs->lock);
task_unlock(tsk);
if (kill)
free_fs_struct(fs);
}
}
struct fs_struct *copy_fs_struct(struct fs_struct *old)
{
struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
/* We don't need to lock fs - think why ;-) */
if (fs) {
fs->users = 1;
fs->in_exec = 0;
spin_lock_init(&fs->lock);
seqcount_init(&fs->seq);
fs->umask = old->umask;
spin_lock(&old->lock);
fs->root = old->root;
path_get(&fs->root);
fs->pwd = old->pwd;
path_get(&fs->pwd);
spin_unlock(&old->lock);
}
return fs;
}
int unshare_fs_struct(void)
{
struct fs_struct *fs = current->fs;
struct fs_struct *new_fs = copy_fs_struct(fs);
int kill;
if (!new_fs)
return -ENOMEM;
task_lock(current);
spin_lock(&fs->lock);
kill = !--fs->users;
current->fs = new_fs;
spin_unlock(&fs->lock);
task_unlock(current);
if (kill)
free_fs_struct(fs);
return 0;
}
EXPORT_SYMBOL_GPL(unshare_fs_struct);
int current_umask(void)
{
return current->fs->umask;
}
EXPORT_SYMBOL(current_umask);
/* to be mentioned only in INIT_TASK */
struct fs_struct init_fs = {
.users = 1,
.lock = __SPIN_LOCK_UNLOCKED(init_fs.lock),
.seq = SEQCNT_ZERO(init_fs.seq),
.umask = 0022,
};