br_read_unlock(&vfsmount_lock);
}
+/*
+ * When we move over from the RCU domain to properly refcounted
+ * long-lived dentries, we need to check the sequence numbers
+ * we got before lookup very carefully.
+ *
+ * We cannot blindly increment a dentry refcount - even if it
+ * is not locked - if it is zero, because it may have gone
+ * through the final d_kill() logic already.
+ *
+ * So for a zero refcount, we need to get the spinlock (which is
+ * safe even for a dead dentry because the de-allocation is
+ * RCU-delayed), and check the sequence count under the lock.
+ *
+ * Once we have checked the sequence count, we know it is live,
+ * and since we hold the spinlock it cannot die from under us.
+ *
+ * In contrast, if the reference count wasn't zero, we can just
+ * increment the lockref without having to take the spinlock.
+ * Even if the sequence number ends up being stale, we haven't
+ * gone through the final dput() and killed the dentry yet.
+ */
+static inline int d_rcu_to_refcount(struct dentry *dentry, seqcount_t *validate, unsigned seq)
+{
+ int gotref;
+
+ gotref = lockref_get_or_lock(&dentry->d_lockref);
+
+ /* Does the sequence number still match? */
+ if (read_seqcount_retry(validate, seq)) {
+ if (gotref)
+ dput(dentry);
+ else
+ spin_unlock(&dentry->d_lock);
+ return -ECHILD;
+ }
+
+ /* Get the ref now, if we couldn't get it originally */
+ if (!gotref) {
+ dentry->d_lockref.count++;
+ spin_unlock(&dentry->d_lock);
+ }
+ return 0;
+}
+
/**
* unlazy_walk - try to switch to ref-walk mode.
* @nd: nameidata pathwalk data
nd->root.dentry != fs->root.dentry)
goto err_root;
}
- spin_lock(&parent->d_lock);
+
+ /*
+ * For a negative lookup, the lookup sequence point is the parents
+ * sequence point, and it only needs to revalidate the parent dentry.
+ *
+ * For a positive lookup, we need to move both the parent and the
+ * dentry from the RCU domain to be properly refcounted. And the
+ * sequence number in the dentry validates *both* dentry counters,
+ * since we checked the sequence number of the parent after we got
+ * the child sequence number. So we know the parent must still
+ * be valid if the child sequence number is still valid.
+ */
if (!dentry) {
- if (!__d_rcu_to_refcount(parent, nd->seq))
- goto err_parent;
+ if (d_rcu_to_refcount(parent, &parent->d_seq, nd->seq) < 0)
+ goto err_root;
BUG_ON(nd->inode != parent->d_inode);
} else {
- if (dentry->d_parent != parent)
+ if (d_rcu_to_refcount(dentry, &dentry->d_seq, nd->seq) < 0)
+ goto err_root;
+ if (d_rcu_to_refcount(parent, &dentry->d_seq, nd->seq) < 0)
goto err_parent;
- spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
- if (!__d_rcu_to_refcount(dentry, nd->seq))
- goto err_child;
- /*
- * If the sequence check on the child dentry passed, then
- * the child has not been removed from its parent. This
- * means the parent dentry must be valid and able to take
- * a reference at this point.
- */
- BUG_ON(!IS_ROOT(dentry) && dentry->d_parent != parent);
- BUG_ON(!parent->d_count);
- parent->d_count++;
- spin_unlock(&dentry->d_lock);
}
- spin_unlock(&parent->d_lock);
if (want_root) {
path_get(&nd->root);
spin_unlock(&fs->lock);
nd->flags &= ~LOOKUP_RCU;
return 0;
-err_child:
- spin_unlock(&dentry->d_lock);
err_parent:
- spin_unlock(&parent->d_lock);
+ dput(dentry);
err_root:
if (want_root)
spin_unlock(&fs->lock);
nd->flags &= ~LOOKUP_RCU;
if (!(nd->flags & LOOKUP_ROOT))
nd->root.mnt = NULL;
- spin_lock(&dentry->d_lock);
- if (unlikely(!__d_rcu_to_refcount(dentry, nd->seq))) {
- spin_unlock(&dentry->d_lock);
+
+ if (d_rcu_to_refcount(dentry, &dentry->d_seq, nd->seq) < 0) {
unlock_rcu_walk();
return -ECHILD;
}
- BUG_ON(nd->inode != dentry->d_inode);
- spin_unlock(&dentry->d_lock);
mntget(nd->path.mnt);
unlock_rcu_walk();
}
return s;
}
+/**
+ * umount_lookup_last - look up last component for umount
+ * @nd: pathwalk nameidata - currently pointing at parent directory of "last"
+ * @path: pointer to container for result
+ *
+ * This is a special lookup_last function just for umount. In this case, we
+ * need to resolve the path without doing any revalidation.
+ *
+ * The nameidata should be the result of doing a LOOKUP_PARENT pathwalk. Since
+ * mountpoints are always pinned in the dcache, their ancestors are too. Thus,
+ * in almost all cases, this lookup will be served out of the dcache. The only
+ * cases where it won't are if nd->last refers to a symlink or the path is
+ * bogus and it doesn't exist.
+ *
+ * Returns:
+ * -error: if there was an error during lookup. This includes -ENOENT if the
+ * lookup found a negative dentry. The nd->path reference will also be
+ * put in this case.
+ *
+ * 0: if we successfully resolved nd->path and found it to not to be a
+ * symlink that needs to be followed. "path" will also be populated.
+ * The nd->path reference will also be put.
+ *
+ * 1: if we successfully resolved nd->last and found it to be a symlink
+ * that needs to be followed. "path" will be populated with the path
+ * to the link, and nd->path will *not* be put.
+ */
+static int
+umount_lookup_last(struct nameidata *nd, struct path *path)
+{
+ int error = 0;
+ struct dentry *dentry;
+ struct dentry *dir = nd->path.dentry;
+
+ if (unlikely(nd->flags & LOOKUP_RCU)) {
+ WARN_ON_ONCE(1);
+ error = -ECHILD;
+ goto error_check;
+ }
+
+ nd->flags &= ~LOOKUP_PARENT;
+
+ if (unlikely(nd->last_type != LAST_NORM)) {
+ error = handle_dots(nd, nd->last_type);
+ if (!error)
+ dentry = dget(nd->path.dentry);
+ goto error_check;
+ }
+
+ mutex_lock(&dir->d_inode->i_mutex);
+ dentry = d_lookup(dir, &nd->last);
+ if (!dentry) {
+ /*
+ * No cached dentry. Mounted dentries are pinned in the cache,
+ * so that means that this dentry is probably a symlink or the
+ * path doesn't actually point to a mounted dentry.
+ */
+ dentry = d_alloc(dir, &nd->last);
+ if (!dentry) {
+ error = -ENOMEM;
+ } else {
+ dentry = lookup_real(dir->d_inode, dentry, nd->flags);
+ if (IS_ERR(dentry))
+ error = PTR_ERR(dentry);
+ }
+ }
+ mutex_unlock(&dir->d_inode->i_mutex);
+
+error_check:
+ if (!error) {
+ if (!dentry->d_inode) {
+ error = -ENOENT;
+ dput(dentry);
+ } else {
+ path->dentry = dentry;
+ path->mnt = mntget(nd->path.mnt);
+ if (should_follow_link(dentry->d_inode,
+ nd->flags & LOOKUP_FOLLOW))
+ return 1;
+ follow_mount(path);
+ }
+ }
+ terminate_walk(nd);
+ return error;
+}
+
+/**
+ * path_umountat - look up a path to be umounted
+ * @dfd: directory file descriptor to start walk from
+ * @name: full pathname to walk
+ * @flags: lookup flags
+ * @nd: pathwalk nameidata
+ *
+ * Look up the given name, but don't attempt to revalidate the last component.
+ * Returns 0 and "path" will be valid on success; Retuns error otherwise.
+ */
+static int
+path_umountat(int dfd, const char *name, struct path *path, unsigned int flags)
+{
+ struct file *base = NULL;
+ struct nameidata nd;
+ int err;
+
+ err = path_init(dfd, name, flags | LOOKUP_PARENT, &nd, &base);
+ if (unlikely(err))
+ return err;
+
+ current->total_link_count = 0;
+ err = link_path_walk(name, &nd);
+ if (err)
+ goto out;
+
+ /* If we're in rcuwalk, drop out of it to handle last component */
+ if (nd.flags & LOOKUP_RCU) {
+ err = unlazy_walk(&nd, NULL);
+ if (err) {
+ terminate_walk(&nd);
+ goto out;
+ }
+ }
+
+ err = umount_lookup_last(&nd, path);
+ while (err > 0) {
+ void *cookie;
+ struct path link = *path;
+ err = may_follow_link(&link, &nd);
+ if (unlikely(err))
+ break;
+ nd.flags |= LOOKUP_PARENT;
+ err = follow_link(&link, &nd, &cookie);
+ if (err)
+ break;
+ err = umount_lookup_last(&nd, path);
+ put_link(&nd, &link, cookie);
+ }
+out:
+ if (base)
+ fput(base);
+
+ if (nd.root.mnt && !(nd.flags & LOOKUP_ROOT))
+ path_put(&nd.root);
+
+ return err;
+}
+
+/**
+ * user_path_umountat - lookup a path from userland in order to umount it
+ * @dfd: directory file descriptor
+ * @name: pathname from userland
+ * @flags: lookup flags
+ * @path: pointer to container to hold result
+ *
+ * A umount is a special case for path walking. We're not actually interested
+ * in the inode in this situation, and ESTALE errors can be a problem. We
+ * simply want track down the dentry and vfsmount attached at the mountpoint
+ * and avoid revalidating the last component.
+ *
+ * Returns 0 and populates "path" on success.
+ */
+int
+user_path_umountat(int dfd, const char __user *name, unsigned int flags,
+ struct path *path)
+{
+ struct filename *s = getname(name);
+ int error;
+
+ if (IS_ERR(s))
+ return PTR_ERR(s);
+
+ error = path_umountat(dfd, s->name, path, flags | LOOKUP_RCU);
+ if (unlikely(error == -ECHILD))
+ error = path_umountat(dfd, s->name, path, flags);
+ if (unlikely(error == -ESTALE))
+ error = path_umountat(dfd, s->name, path, flags | LOOKUP_REVAL);
+
+ if (likely(!error))
+ audit_inode(s, path->dentry, 0);
+
+ putname(s);
+ return error;
+}
+
/*
* It's inline, so penalty for filesystems that don't use sticky bit is
* minimal.
{
shrink_dcache_parent(dentry);
spin_lock(&dentry->d_lock);
- if (dentry->d_count == 1)
+ if (dentry->d_lockref.count == 1)
__d_drop(dentry);
spin_unlock(&dentry->d_lock);
}
if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0)
return -EINVAL;
/*
- * Using empty names is equivalent to using AT_SYMLINK_FOLLOW
- * on /proc/self/fd/<fd>.
+ * To use null names we require CAP_DAC_READ_SEARCH
+ * This ensures that not everyone will be able to create
+ * handlink using the passed filedescriptor.
*/
- if (flags & AT_EMPTY_PATH)
+ if (flags & AT_EMPTY_PATH) {
+ if (!capable(CAP_DAC_READ_SEARCH))
+ return -ENOENT;
how = LOOKUP_EMPTY;
+ }
if (flags & AT_SYMLINK_FOLLOW)
how |= LOOKUP_FOLLOW;
projects / linux-2.6-block.git / blobdiff