![Eric W. Biederman](/assets/img/avatar_default.png)
Only allow unprivileged mounts of proc and sysfs if they are already mounted when the user namespace is created. proc and sysfs are interesting because they have content that is per namespace, and so fresh mounts are needed when new namespaces are created while at the same time proc and sysfs have content that is shared between every instance. Respect the policy of who may see the shared content of proc and sysfs by only allowing new mounts if there was an existing mount at the time the user namespace was created. In practice there are only two interesting cases: proc and sysfs are mounted at their usual places, proc and sysfs are not mounted at all (some form of mount namespace jail). Cc: stable@vger.kernel.org Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
206 lines
4.6 KiB
C
206 lines
4.6 KiB
C
/*
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* fs/sysfs/symlink.c - operations for initializing and mounting sysfs
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*
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* Copyright (c) 2001-3 Patrick Mochel
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* Copyright (c) 2007 SUSE Linux Products GmbH
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* Copyright (c) 2007 Tejun Heo <teheo@suse.de>
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*
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* This file is released under the GPLv2.
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*
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* Please see Documentation/filesystems/sysfs.txt for more information.
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*/
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#define DEBUG
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#include <linux/fs.h>
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#include <linux/mount.h>
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#include <linux/pagemap.h>
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/magic.h>
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#include <linux/slab.h>
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#include <linux/user_namespace.h>
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#include "sysfs.h"
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static struct vfsmount *sysfs_mnt;
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struct kmem_cache *sysfs_dir_cachep;
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static const struct super_operations sysfs_ops = {
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.statfs = simple_statfs,
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.drop_inode = generic_delete_inode,
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.evict_inode = sysfs_evict_inode,
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};
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struct sysfs_dirent sysfs_root = {
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.s_name = "",
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.s_count = ATOMIC_INIT(1),
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.s_flags = SYSFS_DIR | (KOBJ_NS_TYPE_NONE << SYSFS_NS_TYPE_SHIFT),
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.s_mode = S_IFDIR | S_IRUGO | S_IXUGO,
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.s_ino = 1,
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};
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static int sysfs_fill_super(struct super_block *sb, void *data, int silent)
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{
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struct inode *inode;
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struct dentry *root;
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sb->s_blocksize = PAGE_CACHE_SIZE;
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sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
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sb->s_magic = SYSFS_MAGIC;
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sb->s_op = &sysfs_ops;
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sb->s_time_gran = 1;
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/* get root inode, initialize and unlock it */
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mutex_lock(&sysfs_mutex);
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inode = sysfs_get_inode(sb, &sysfs_root);
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mutex_unlock(&sysfs_mutex);
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if (!inode) {
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pr_debug("sysfs: could not get root inode\n");
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return -ENOMEM;
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}
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/* instantiate and link root dentry */
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root = d_make_root(inode);
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if (!root) {
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pr_debug("%s: could not get root dentry!\n",__func__);
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return -ENOMEM;
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}
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root->d_fsdata = &sysfs_root;
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sb->s_root = root;
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sb->s_d_op = &sysfs_dentry_ops;
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return 0;
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}
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static int sysfs_test_super(struct super_block *sb, void *data)
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{
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struct sysfs_super_info *sb_info = sysfs_info(sb);
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struct sysfs_super_info *info = data;
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enum kobj_ns_type type;
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int found = 1;
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for (type = KOBJ_NS_TYPE_NONE; type < KOBJ_NS_TYPES; type++) {
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if (sb_info->ns[type] != info->ns[type])
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found = 0;
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}
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return found;
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}
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static int sysfs_set_super(struct super_block *sb, void *data)
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{
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int error;
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error = set_anon_super(sb, data);
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if (!error)
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sb->s_fs_info = data;
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return error;
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}
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static void free_sysfs_super_info(struct sysfs_super_info *info)
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{
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int type;
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for (type = KOBJ_NS_TYPE_NONE; type < KOBJ_NS_TYPES; type++)
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kobj_ns_drop(type, info->ns[type]);
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kfree(info);
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}
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static struct dentry *sysfs_mount(struct file_system_type *fs_type,
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int flags, const char *dev_name, void *data)
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{
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struct sysfs_super_info *info;
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enum kobj_ns_type type;
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struct super_block *sb;
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int error;
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if (!(flags & MS_KERNMOUNT) && !current_user_ns()->may_mount_sysfs)
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return ERR_PTR(-EPERM);
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info = kzalloc(sizeof(*info), GFP_KERNEL);
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if (!info)
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return ERR_PTR(-ENOMEM);
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for (type = KOBJ_NS_TYPE_NONE; type < KOBJ_NS_TYPES; type++)
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info->ns[type] = kobj_ns_grab_current(type);
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sb = sget(fs_type, sysfs_test_super, sysfs_set_super, flags, info);
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if (IS_ERR(sb) || sb->s_fs_info != info)
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free_sysfs_super_info(info);
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if (IS_ERR(sb))
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return ERR_CAST(sb);
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if (!sb->s_root) {
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error = sysfs_fill_super(sb, data, flags & MS_SILENT ? 1 : 0);
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if (error) {
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deactivate_locked_super(sb);
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return ERR_PTR(error);
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}
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sb->s_flags |= MS_ACTIVE;
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}
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return dget(sb->s_root);
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}
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static void sysfs_kill_sb(struct super_block *sb)
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{
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struct sysfs_super_info *info = sysfs_info(sb);
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/* Remove the superblock from fs_supers/s_instances
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* so we can't find it, before freeing sysfs_super_info.
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*/
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kill_anon_super(sb);
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free_sysfs_super_info(info);
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}
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static struct file_system_type sysfs_fs_type = {
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.name = "sysfs",
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.mount = sysfs_mount,
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.kill_sb = sysfs_kill_sb,
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.fs_flags = FS_USERNS_MOUNT,
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};
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int __init sysfs_init(void)
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{
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int err = -ENOMEM;
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sysfs_dir_cachep = kmem_cache_create("sysfs_dir_cache",
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sizeof(struct sysfs_dirent),
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0, 0, NULL);
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if (!sysfs_dir_cachep)
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goto out;
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err = sysfs_inode_init();
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if (err)
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goto out_err;
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err = register_filesystem(&sysfs_fs_type);
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if (!err) {
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sysfs_mnt = kern_mount(&sysfs_fs_type);
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if (IS_ERR(sysfs_mnt)) {
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printk(KERN_ERR "sysfs: could not mount!\n");
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err = PTR_ERR(sysfs_mnt);
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sysfs_mnt = NULL;
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unregister_filesystem(&sysfs_fs_type);
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goto out_err;
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}
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} else
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goto out_err;
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out:
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return err;
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out_err:
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kmem_cache_destroy(sysfs_dir_cachep);
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sysfs_dir_cachep = NULL;
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goto out;
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}
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#undef sysfs_get
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struct sysfs_dirent *sysfs_get(struct sysfs_dirent *sd)
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{
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return __sysfs_get(sd);
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}
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EXPORT_SYMBOL_GPL(sysfs_get);
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#undef sysfs_put
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void sysfs_put(struct sysfs_dirent *sd)
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{
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__sysfs_put(sd);
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}
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EXPORT_SYMBOL_GPL(sysfs_put);
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