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Commit 1b852bce authored by Eric W. Biederman's avatar Eric W. Biederman
Browse files

mnt: Refactor the logic for mounting sysfs and proc in a user namespace 



Fresh mounts of proc and sysfs are a very special case that works very
much like a bind mount.  Unfortunately the current structure can not
preserve the MNT_LOCK... mount flags.  Therefore refactor the logic
into a form that can be modified to preserve those lock bits.

Add a new filesystem flag FS_USERNS_VISIBLE that requires some mount
of the filesystem be fully visible in the current mount namespace,
before the filesystem may be mounted.

Move the logic for calling fs_fully_visible from proc and sysfs into
fs/namespace.c where it has greater access to mount namespace state.

Cc: stable@vger.kernel.org
Signed-off-by: default avatar"Eric W. Biederman" <ebiederm@xmission.com>
parent 7e96c1b0

fs/namespace.c

+7 −1
Original line number Diff line number Diff line
@@ -2332,6 +2332,8 @@ static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags) 
	return err;

}



static bool fs_fully_visible(struct file_system_type *fs_type);



/*

 * create a new mount for userspace and request it to be added into the

 * namespace's tree
@@ -2363,6 +2365,10 @@ static int do_new_mount(struct path *path, const char *fstype, int flags, 
			flags |= MS_NODEV;

			mnt_flags |= MNT_NODEV | MNT_LOCK_NODEV;

		}

		if (type->fs_flags & FS_USERNS_VISIBLE) {

			if (!fs_fully_visible(type))

				return -EPERM;

		}

	}



	mnt = vfs_kern_mount(type, flags, name, data);
@@ -3164,7 +3170,7 @@ bool current_chrooted(void) 
	return chrooted;

}



bool fs_fully_visible(struct file_system_type *type)

static bool fs_fully_visible(struct file_system_type *type)

{

	struct mnt_namespace *ns = current->nsproxy->mnt_ns;

	struct mount *mnt;

fs/proc/root.c

+1 −4
Original line number Diff line number Diff line
@@ -112,9 +112,6 @@ static struct dentry *proc_mount(struct file_system_type *fs_type, 
		ns = task_active_pid_ns(current);

		options = data;



		if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))

			return ERR_PTR(-EPERM);



		/* Does the mounter have privilege over the pid namespace? */

		if (!ns_capable(ns->user_ns, CAP_SYS_ADMIN))

			return ERR_PTR(-EPERM);
@@ -159,7 +156,7 @@ static struct file_system_type proc_fs_type = { 
	.name		= "proc",

	.mount		= proc_mount,

	.kill_sb	= proc_kill_sb,

	.fs_flags	= FS_USERNS_MOUNT,

	.fs_flags	= FS_USERNS_VISIBLE | FS_USERNS_MOUNT,

};



void __init proc_root_init(void)

fs/sysfs/mount.c

+1 −4
Original line number Diff line number Diff line
@@ -31,9 +31,6 @@ static struct dentry *sysfs_mount(struct file_system_type *fs_type, 
	bool new_sb;



	if (!(flags & MS_KERNMOUNT)) {

		if (!capable(CAP_SYS_ADMIN) && !fs_fully_visible(fs_type))

			return ERR_PTR(-EPERM);



		if (!kobj_ns_current_may_mount(KOBJ_NS_TYPE_NET))

			return ERR_PTR(-EPERM);

	}
@@ -58,7 +55,7 @@ static struct file_system_type sysfs_fs_type = { 
	.name		= "sysfs",

	.mount		= sysfs_mount,

	.kill_sb	= sysfs_kill_sb,

	.fs_flags	= FS_USERNS_MOUNT,

	.fs_flags	= FS_USERNS_VISIBLE | FS_USERNS_MOUNT,

};



int __init sysfs_init(void)

include/linux/fs.h

+1 −1
Original line number Diff line number Diff line
@@ -1897,6 +1897,7 @@ struct file_system_type { 
#define FS_HAS_SUBTYPE		4

#define FS_USERNS_MOUNT		8	/* Can be mounted by userns root */

#define FS_USERNS_DEV_MOUNT	16 /* A userns mount does not imply MNT_NODEV */

#define FS_USERNS_VISIBLE	32	/* FS must already be visible */

#define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move() during rename() internally. */

	struct dentry *(*mount) (struct file_system_type *, int,

		       const char *, void *);
@@ -1984,7 +1985,6 @@ extern int vfs_ustat(dev_t, struct kstatfs *); 
extern int freeze_super(struct super_block *super);

extern int thaw_super(struct super_block *super);

extern bool our_mnt(struct vfsmount *mnt);

extern bool fs_fully_visible(struct file_system_type *);



extern int current_umask(void);