Re: [patch 3/8] account user mounts

[Eric W. Biederman]

Miklos Szeredi <miklos@xxxxxxxxxx> writes:

> From: Miklos Szeredi <mszeredi@xxxxxxx>
>
> Add sysctl variables for accounting and limiting the number of user
> mounts.
>
> The maximum number of user mounts is set to 1024 by default.  This
> won't in itself enable user mounts, setting a mount to be owned by a
> user is first needed

Since each mount has a user can we just make this a per user rlimit?

If we are going to implement a sysctl at this point I think it should
be a global limit that doesn't care if who you are.  Even root can
have recursive mounts that attempt to get out of control.

Also currently you are not checking the max_users.  It looks like
you do this in a later patch but still it is a little strange to
allow user own mounts and have accounting but to not check the
limit at this state.

Eric

>
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
> ---
>
> Index: linux/include/linux/sysctl.h
> ===================================================================
> --- linux.orig/include/linux/sysctl.h	2007-04-20 11:55:02.000000000 +0200
> +++ linux/include/linux/sysctl.h	2007-04-20 11:55:07.000000000 +0200
> @@ -818,6 +818,8 @@ enum
>  	FS_AIO_NR=18,	/* current system-wide number of aio requests */
>  	FS_AIO_MAX_NR=19, /* system-wide maximum number of aio requests */
>  	FS_INOTIFY=20,	/* inotify submenu */
> +	FS_NR_USER_MOUNTS=21,	/* int:current number of user mounts */
> +	FS_MAX_USER_MOUNTS=22,	/* int:maximum number of user mounts */
>  	FS_OCFS2=988,	/* ocfs2 */
>  };
>  
> Index: linux/kernel/sysctl.c
> ===================================================================
> --- linux.orig/kernel/sysctl.c	2007-04-20 11:55:02.000000000 +0200
> +++ linux/kernel/sysctl.c	2007-04-20 11:55:07.000000000 +0200
> @@ -1063,6 +1063,22 @@ static ctl_table fs_table[] = {
>  #endif	
>  #endif
>  	{
> +		.ctl_name	= FS_NR_USER_MOUNTS,
> +		.procname	= "nr_user_mounts",
> +		.data		= &nr_user_mounts,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0444,
> +		.proc_handler	= &proc_dointvec,
> +	},
> +	{
> +		.ctl_name	= FS_MAX_USER_MOUNTS,
> +		.procname	= "max_user_mounts",
> +		.data		= &max_user_mounts,
> +		.maxlen		= sizeof(int),
> +		.mode		= 0644,
> +		.proc_handler	= &proc_dointvec,
> +	},
> +	{
>  		.ctl_name	= KERN_SETUID_DUMPABLE,
>  		.procname	= "suid_dumpable",
>  		.data		= &suid_dumpable,
> Index: linux/Documentation/filesystems/proc.txt
> ===================================================================
> --- linux.orig/Documentation/filesystems/proc.txt 2007-04-20 11:55:02.000000000
> +0200
> +++ linux/Documentation/filesystems/proc.txt 2007-04-20 11:55:07.000000000 +0200
> @@ -923,6 +923,15 @@ reaches aio-max-nr then io_setup will fa
>  raising aio-max-nr does not result in the pre-allocation or re-sizing
>  of any kernel data structures.
>  
> +nr_user_mounts and max_user_mounts
> +----------------------------------
> +
> +These represent the number of "user" mounts and the maximum number of
> +"user" mounts respectively.  User mounts may be created by
> +unprivileged users.  User mounts may also be created with sysadmin
> +privileges on behalf of a user, in which case nr_user_mounts may
> +exceed max_user_mounts.
> +
>  2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats
>  -----------------------------------------------------------
>  
> Index: linux/fs/namespace.c
> ===================================================================
> --- linux.orig/fs/namespace.c	2007-04-20 11:55:06.000000000 +0200
> +++ linux/fs/namespace.c	2007-04-20 11:55:07.000000000 +0200
> @@ -39,6 +39,9 @@ static int hash_mask __read_mostly, hash
>  static struct kmem_cache *mnt_cache __read_mostly;
>  static struct rw_semaphore namespace_sem;
>  
> +int nr_user_mounts;
> +int max_user_mounts = 1024;
> +
>  /* /sys/fs */
>  decl_subsys(fs, NULL, NULL);
>  EXPORT_SYMBOL_GPL(fs_subsys);
> @@ -227,11 +230,30 @@ static struct vfsmount *skip_mnt_tree(st
>  	return p;
>  }
>  
> +static void dec_nr_user_mounts(void)
> +{
> +	spin_lock(&vfsmount_lock);
> +	nr_user_mounts--;
> +	spin_unlock(&vfsmount_lock);
> +}
> +
>  static void set_mnt_user(struct vfsmount *mnt)
>  {
>  	BUG_ON(mnt->mnt_flags & MNT_USER);
>  	mnt->mnt_uid = current->uid;
>  	mnt->mnt_flags |= MNT_USER;
> +	spin_lock(&vfsmount_lock);
> +	nr_user_mounts++;
> +	spin_unlock(&vfsmount_lock);
> +}
> +
> +static void clear_mnt_user(struct vfsmount *mnt)
> +{
> +	if (mnt->mnt_flags & MNT_USER) {
> +		mnt->mnt_uid = 0;
> +		mnt->mnt_flags &= ~MNT_USER;
> +		dec_nr_user_mounts();
> +	}
>  }
>  
>  static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
> @@ -283,6 +305,7 @@ static inline void __mntput(struct vfsmo
>  {
>  	struct super_block *sb = mnt->mnt_sb;
>  	dput(mnt->mnt_root);
> +	clear_mnt_user(mnt);
>  	free_vfsmnt(mnt);
>  	deactivate_super(sb);
>  }
> @@ -1023,6 +1046,7 @@ static int do_remount(struct nameidata *
>  	down_write(&sb->s_umount);
>  	err = do_remount_sb(sb, flags, data, 0);
>  	if (!err) {
> +		clear_mnt_user(nd->mnt);
>  		nd->mnt->mnt_flags = mnt_flags;
>  		if (flags & MS_SETUSER)
>  			set_mnt_user(nd->mnt);
> Index: linux/include/linux/fs.h
> ===================================================================
> --- linux.orig/include/linux/fs.h	2007-04-20 11:55:05.000000000 +0200
> +++ linux/include/linux/fs.h	2007-04-20 11:55:07.000000000 +0200
> @@ -50,6 +50,9 @@ extern struct inodes_stat_t inodes_stat;
>  
>  extern int leases_enable, lease_break_time;
>  
> +extern int nr_user_mounts;
> +extern int max_user_mounts;
> +
>  #ifdef CONFIG_DNOTIFY
>  extern int dir_notify_enable;
>  #endif
>
> --
-
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