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Message-ID: <20080114215351.GC6704@sergelap.austin.ibm.com>
Date: Mon, 14 Jan 2008 15:53:51 -0600
From: "Serge E. Hallyn" <serue@...ibm.com>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: akpm@...ux-foundation.org, hch@...radead.org, serue@...ibm.com,
viro@....linux.org.uk, ebiederm@...ssion.com, kzak@...hat.com,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
containers@...ts.osdl.org, util-linux-ng@...r.kernel.org
Subject: Re: [patch 3/9] unprivileged mounts: account user mounts
Quoting Miklos Szeredi (miklos@...redi.hu):
> From: Miklos Szeredi <mszeredi@...e.cz>
>
> 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
>
> [akpm]
> - don't use enumerated sysctls
>
> Signed-off-by: Miklos Szeredi <mszeredi@...e.cz>
Seems sane enough, given your responses to Dave.
Acked-by: Serge Hallyn <serue@...ibm.com>
> ---
>
> Index: linux/Documentation/filesystems/proc.txt
> ===================================================================
> --- linux.orig/Documentation/filesystems/proc.txt 2008-01-03 17:12:58.000000000 +0100
> +++ linux/Documentation/filesystems/proc.txt 2008-01-03 21:15:35.000000000 +0100
> @@ -1012,6 +1012,15 @@ 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 2008-01-03 21:14:16.000000000 +0100
> +++ linux/fs/namespace.c 2008-01-03 21:15:35.000000000 +0100
> @@ -44,6 +44,9 @@ static struct list_head *mount_hashtable
> 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 */
> struct kobject *fs_kobj;
> EXPORT_SYMBOL_GPL(fs_kobj);
> @@ -477,11 +480,30 @@ 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->fsuid;
> 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,
> @@ -542,6 +564,7 @@ static inline void __mntput(struct vfsmo
> */
> WARN_ON(atomic_read(&mnt->__mnt_writers));
> dput(mnt->mnt_root);
> + clear_mnt_user(mnt);
> free_vfsmnt(mnt);
> deactivate_super(sb);
> }
> @@ -1306,6 +1329,7 @@ static int do_remount(struct nameidata *
> else
> err = do_remount_sb(sb, flags, data, 0);
> if (!err) {
> + clear_mnt_user(nd->path.mnt);
> nd->path.mnt->mnt_flags = mnt_flags;
> if (flags & MS_SETUSER)
> set_mnt_user(nd->path.mnt);
> Index: linux/include/linux/fs.h
> ===================================================================
> --- linux.orig/include/linux/fs.h 2008-01-03 20:52:38.000000000 +0100
> +++ linux/include/linux/fs.h 2008-01-03 21:15:35.000000000 +0100
> @@ -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
> Index: linux/kernel/sysctl.c
> ===================================================================
> --- linux.orig/kernel/sysctl.c 2008-01-03 17:13:22.000000000 +0100
> +++ linux/kernel/sysctl.c 2008-01-03 21:15:35.000000000 +0100
> @@ -1288,6 +1288,22 @@ static struct ctl_table fs_table[] = {
> #endif
> #endif
> {
> + .ctl_name = CTL_UNNUMBERED,
> + .procname = "nr_user_mounts",
> + .data = &nr_user_mounts,
> + .maxlen = sizeof(int),
> + .mode = 0444,
> + .proc_handler = &proc_dointvec,
> + },
> + {
> + .ctl_name = CTL_UNNUMBERED,
> + .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,
>
> --
--
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