return s;
}
+/**
+ * mountpoint_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
+mountpoint_last(struct nameidata *nd, struct path *path)
+{
+ int error = 0;
+ struct dentry *dentry;
+ struct dentry *dir = nd->path.dentry;
+
+ /* If we're in rcuwalk, drop out of it to handle last component */
+ if (nd->flags & LOOKUP_RCU) {
+ if (unlazy_walk(nd, NULL)) {
+ error = -ECHILD;
+ goto out;
+ }
+ }
+
+ nd->flags &= ~LOOKUP_PARENT;
+
+ if (unlikely(nd->last_type != LAST_NORM)) {
+ error = handle_dots(nd, nd->last_type);
+ if (error)
+ goto out;
+ dentry = dget(nd->path.dentry);
+ goto done;
+ }
+
+ 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;
+ goto out;
+ }
+ dentry = lookup_real(dir->d_inode, dentry, nd->flags);
+ error = PTR_ERR(dentry);
+ if (IS_ERR(dentry))
+ goto out;
+ }
+ mutex_unlock(&dir->d_inode->i_mutex);
+
+done:
+ if (!dentry->d_inode) {
+ error = -ENOENT;
+ dput(dentry);
+ goto out;
+ }
+ 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);
+ error = 0;
+out:
+ terminate_walk(nd);
+ return error;
+}
+
+/**
+ * path_mountpoint - look up a path to be umounted
+ * @dfd: directory file descriptor to start walk from
+ * @name: full pathname to walk
+ * @flags: lookup flags
+ *
+ * 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_mountpoint(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;
+
+ err = mountpoint_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 = mountpoint_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_mountpoint_at - 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_mountpoint_at(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_mountpoint(dfd, s->name, path, flags | LOOKUP_RCU);
+ if (unlikely(error == -ECHILD))
+ error = path_mountpoint(dfd, s->name, path, flags);
+ if (unlikely(error == -ESTALE))
+ error = path_mountpoint(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.
projects / ~andy / linux / blobdiff