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![Christian Brauner](/assets/img/avatar_default.png)
Extend some inode methods with an additional user namespace argument. A filesystem that is aware of idmapped mounts will receive the user namespace the mount has been marked with. This can be used for additional permission checking and also to enable filesystems to translate between uids and gids if they need to. We have implemented all relevant helpers in earlier patches. As requested we simply extend the exisiting inode method instead of introducing new ones. This is a little more code churn but it's mostly mechanical and doesnt't leave us with additional inode methods. Link: https://lore.kernel.org/r/20210121131959.646623-25-christian.brauner@ubuntu.com Cc: Christoph Hellwig <hch@lst.de> Cc: David Howells <dhowells@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
272 lines
6.8 KiB
C
272 lines
6.8 KiB
C
// SPDX-License-Identifier: GPL-2.0-or-later
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/* -*- mode: c; c-basic-offset: 8; -*-
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* vim: noexpandtab sw=8 ts=8 sts=0:
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*
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* symlink.c - operations for configfs symlinks.
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*
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* Based on sysfs:
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* sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
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*
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* configfs Copyright (C) 2005 Oracle. All rights reserved.
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*/
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#include <linux/fs.h>
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#include <linux/module.h>
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#include <linux/namei.h>
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#include <linux/slab.h>
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#include <linux/configfs.h>
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#include "configfs_internal.h"
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/* Protects attachments of new symlinks */
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DEFINE_MUTEX(configfs_symlink_mutex);
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static int item_depth(struct config_item * item)
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{
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struct config_item * p = item;
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int depth = 0;
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do { depth++; } while ((p = p->ci_parent) && !configfs_is_root(p));
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return depth;
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}
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static int item_path_length(struct config_item * item)
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{
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struct config_item * p = item;
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int length = 1;
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do {
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length += strlen(config_item_name(p)) + 1;
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p = p->ci_parent;
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} while (p && !configfs_is_root(p));
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return length;
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}
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static void fill_item_path(struct config_item * item, char * buffer, int length)
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{
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struct config_item * p;
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--length;
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for (p = item; p && !configfs_is_root(p); p = p->ci_parent) {
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int cur = strlen(config_item_name(p));
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/* back up enough to print this bus id with '/' */
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length -= cur;
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memcpy(buffer + length, config_item_name(p), cur);
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*(buffer + --length) = '/';
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}
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}
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static int configfs_get_target_path(struct config_item *item,
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struct config_item *target, char *path)
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{
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int depth, size;
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char *s;
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depth = item_depth(item);
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size = item_path_length(target) + depth * 3 - 1;
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if (size > PATH_MAX)
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return -ENAMETOOLONG;
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pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);
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for (s = path; depth--; s += 3)
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strcpy(s,"../");
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fill_item_path(target, path, size);
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pr_debug("%s: path = '%s'\n", __func__, path);
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return 0;
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}
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static int create_link(struct config_item *parent_item,
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struct config_item *item,
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struct dentry *dentry)
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{
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struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
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char *body;
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int ret;
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if (!configfs_dirent_is_ready(target_sd))
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return -ENOENT;
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body = kzalloc(PAGE_SIZE, GFP_KERNEL);
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if (!body)
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return -ENOMEM;
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configfs_get(target_sd);
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spin_lock(&configfs_dirent_lock);
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if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
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spin_unlock(&configfs_dirent_lock);
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configfs_put(target_sd);
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kfree(body);
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return -ENOENT;
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}
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target_sd->s_links++;
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spin_unlock(&configfs_dirent_lock);
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ret = configfs_get_target_path(parent_item, item, body);
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if (!ret)
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ret = configfs_create_link(target_sd, parent_item->ci_dentry,
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dentry, body);
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if (ret) {
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spin_lock(&configfs_dirent_lock);
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target_sd->s_links--;
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spin_unlock(&configfs_dirent_lock);
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configfs_put(target_sd);
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kfree(body);
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}
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return ret;
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}
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static int get_target(const char *symname, struct path *path,
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struct config_item **target, struct super_block *sb)
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{
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int ret;
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ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, path);
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if (!ret) {
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if (path->dentry->d_sb == sb) {
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*target = configfs_get_config_item(path->dentry);
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if (!*target) {
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ret = -ENOENT;
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path_put(path);
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}
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} else {
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ret = -EPERM;
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path_put(path);
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}
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}
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return ret;
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}
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int configfs_symlink(struct user_namespace *mnt_userns, struct inode *dir,
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struct dentry *dentry, const char *symname)
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{
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int ret;
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struct path path;
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struct configfs_dirent *sd;
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struct config_item *parent_item;
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struct config_item *target_item = NULL;
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const struct config_item_type *type;
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sd = dentry->d_parent->d_fsdata;
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/*
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* Fake invisibility if dir belongs to a group/default groups hierarchy
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* being attached
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*/
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if (!configfs_dirent_is_ready(sd))
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return -ENOENT;
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parent_item = configfs_get_config_item(dentry->d_parent);
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type = parent_item->ci_type;
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ret = -EPERM;
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if (!type || !type->ct_item_ops ||
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!type->ct_item_ops->allow_link)
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goto out_put;
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/*
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* This is really sick. What they wanted was a hybrid of
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* link(2) and symlink(2) - they wanted the target resolved
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* at syscall time (as link(2) would've done), be a directory
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* (which link(2) would've refused to do) *AND* be a deep
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* fucking magic, making the target busy from rmdir POV.
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* symlink(2) is nothing of that sort, and the locking it
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* gets matches the normal symlink(2) semantics. Without
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* attempts to resolve the target (which might very well
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* not even exist yet) done prior to locking the parent
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* directory. This perversion, OTOH, needs to resolve
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* the target, which would lead to obvious deadlocks if
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* attempted with any directories locked.
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*
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* Unfortunately, that garbage is userland ABI and we should've
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* said "no" back in 2005. Too late now, so we get to
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* play very ugly games with locking.
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*
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* Try *ANYTHING* of that sort in new code, and you will
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* really regret it. Just ask yourself - what could a BOFH
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* do to me and do I want to find it out first-hand?
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*
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* AV, a thoroughly annoyed bastard.
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*/
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inode_unlock(dir);
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ret = get_target(symname, &path, &target_item, dentry->d_sb);
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inode_lock(dir);
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if (ret)
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goto out_put;
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if (dentry->d_inode || d_unhashed(dentry))
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ret = -EEXIST;
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else
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ret = inode_permission(&init_user_ns, dir,
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MAY_WRITE | MAY_EXEC);
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if (!ret)
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ret = type->ct_item_ops->allow_link(parent_item, target_item);
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if (!ret) {
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mutex_lock(&configfs_symlink_mutex);
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ret = create_link(parent_item, target_item, dentry);
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mutex_unlock(&configfs_symlink_mutex);
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if (ret && type->ct_item_ops->drop_link)
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type->ct_item_ops->drop_link(parent_item,
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target_item);
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}
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config_item_put(target_item);
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path_put(&path);
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out_put:
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config_item_put(parent_item);
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return ret;
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}
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int configfs_unlink(struct inode *dir, struct dentry *dentry)
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{
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struct configfs_dirent *sd = dentry->d_fsdata, *target_sd;
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struct config_item *parent_item;
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const struct config_item_type *type;
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int ret;
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ret = -EPERM; /* What lack-of-symlink returns */
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if (!(sd->s_type & CONFIGFS_ITEM_LINK))
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goto out;
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target_sd = sd->s_element;
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parent_item = configfs_get_config_item(dentry->d_parent);
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type = parent_item->ci_type;
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spin_lock(&configfs_dirent_lock);
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list_del_init(&sd->s_sibling);
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spin_unlock(&configfs_dirent_lock);
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configfs_drop_dentry(sd, dentry->d_parent);
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dput(dentry);
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configfs_put(sd);
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/*
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* drop_link() must be called before
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* decrementing target's ->s_links, so that the order of
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* drop_link(this, target) and drop_item(target) is preserved.
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*/
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if (type && type->ct_item_ops &&
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type->ct_item_ops->drop_link)
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type->ct_item_ops->drop_link(parent_item,
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target_sd->s_element);
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spin_lock(&configfs_dirent_lock);
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target_sd->s_links--;
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spin_unlock(&configfs_dirent_lock);
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configfs_put(target_sd);
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config_item_put(parent_item);
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ret = 0;
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out:
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return ret;
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}
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const struct inode_operations configfs_symlink_inode_operations = {
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.get_link = simple_get_link,
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.setattr = configfs_setattr,
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};
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