[patch 01/10] add user mounts to the kernel

[Miklos Szeredi <miklos@szeredi.hu>]

From: Miklos Szeredi <mszeredi@suse.cz>

Add ownership information to mounts.

A new mount flag, MS_SETUSER is used to make a mount owned by a user.
If this flag is specified, then the owner will be set to the current
real user id and the mount will be marked with the MNT_USER flag.  On
remount don't preserve previous owner, and treat MS_SETUSER as for a
new mount.  The MS_SETUSER flag is ignored on mount move.

The MNT_USER flag is not copied on any kind of mount cloning:
namespace creation, binding or propagation.  For bind mounts the
cloned mount(s) are set to MNT_USER depending on the MS_SETUSER mount
flag.  In all the other cases MNT_USER is always cleared.

For MNT_USER mounts a "user=UID" option is added to /proc/PID/mounts.
This is compatible with how mount ownership is stored in /etc/mtab.

It is expected, that in the future mount(8) will use MS_SETUSER to
store mount ownership within the kernel.  This would help in
situations, where /etc/mtab is difficult or impossible to work with,
e.g. when using mount propagation.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/fs/namespace.c
===================================================================
--- linux.orig/fs/namespace.c	2007-04-13 12:24:15.000000000 +0200
+++ linux/fs/namespace.c	2007-04-13 13:03:44.000000000 +0200
@@ -227,6 +227,13 @@ static struct vfsmount *skip_mnt_tree(st
 	return p;
 }
 
+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;
+}
+
 static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
 					int flag)
 {
@@ -241,6 +248,11 @@ static struct vfsmount *clone_mnt(struct
 		mnt->mnt_mountpoint = mnt->mnt_root;
 		mnt->mnt_parent = mnt;
 
+		/* don't copy the MNT_USER flag */
+		mnt->mnt_flags &= ~MNT_USER;
+		if (flag & CL_SETUSER)
+			set_mnt_user(mnt);
+
 		if (flag & CL_SLAVE) {
 			list_add(&mnt->mnt_slave, &old->mnt_slave_list);
 			mnt->mnt_master = old;
@@ -403,6 +415,8 @@ static int show_vfsmnt(struct seq_file *
 		if (mnt->mnt_flags & fs_infop->flag)
 			seq_puts(m, fs_infop->str);
 	}
+	if (mnt->mnt_flags & MNT_USER)
+		seq_printf(m, ",user=%i", mnt->mnt_uid);
 	if (mnt->mnt_sb->s_op->show_options)
 		err = mnt->mnt_sb->s_op->show_options(m, mnt);
 	seq_puts(m, " 0 0\n");
@@ -920,8 +934,9 @@ static int do_change_type(struct nameida
 /*
  * do loopback mount.
  */
-static int do_loopback(struct nameidata *nd, char *old_name, int recurse)
+static int do_loopback(struct nameidata *nd, char *old_name, int flags)
 {
+	int clone_flags;
 	struct nameidata old_nd;
 	struct vfsmount *mnt = NULL;
 	int err = mount_is_safe(nd);
@@ -941,11 +956,12 @@ static int do_loopback(struct nameidata 
 	if (!check_mnt(nd->mnt) || !check_mnt(old_nd.mnt))
 		goto out;
 
+	clone_flags = (flags & MS_SETUSER) ? CL_SETUSER : 0;
 	err = -ENOMEM;
-	if (recurse)
-		mnt = copy_tree(old_nd.mnt, old_nd.dentry, 0);
+	if (flags & MS_REC)
+		mnt = copy_tree(old_nd.mnt, old_nd.dentry, clone_flags);
 	else
-		mnt = clone_mnt(old_nd.mnt, old_nd.dentry, 0);
+		mnt = clone_mnt(old_nd.mnt, old_nd.dentry, clone_flags);
 
 	if (!mnt)
 		goto out;
@@ -987,8 +1003,11 @@ static int do_remount(struct nameidata *
 
 	down_write(&sb->s_umount);
 	err = do_remount_sb(sb, flags, data, 0);
-	if (!err)
+	if (!err) {
 		nd->mnt->mnt_flags = mnt_flags;
+		if (flags & MS_SETUSER)
+			set_mnt_user(nd->mnt);
+	}
 	up_write(&sb->s_umount);
 	if (!err)
 		security_sb_post_remount(nd->mnt, flags, data);
@@ -1093,10 +1112,13 @@ static int do_new_mount(struct nameidata
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;
 
-	mnt = do_kern_mount(type, flags, name, data);
+	mnt = do_kern_mount(type, flags & ~MS_SETUSER, name, data);
 	if (IS_ERR(mnt))
 		return PTR_ERR(mnt);
 
+	if (flags & MS_SETUSER)
+		set_mnt_user(mnt);
+
 	return do_add_mount(mnt, nd, mnt_flags, NULL);
 }
 
@@ -1127,7 +1149,8 @@ int do_add_mount(struct vfsmount *newmnt
 	if (S_ISLNK(newmnt->mnt_root->d_inode->i_mode))
 		goto unlock;
 
-	newmnt->mnt_flags = mnt_flags;
+	/* MNT_USER was set earlier */
+	newmnt->mnt_flags |= mnt_flags;
 	if ((err = graft_tree(newmnt, nd)))
 		goto unlock;
 
@@ -1447,7 +1470,7 @@ long do_mount(char *dev_name, char *dir_
 		retval = do_remount(&nd, flags & ~MS_REMOUNT, mnt_flags,
 				    data_page);
 	else if (flags & MS_BIND)
-		retval = do_loopback(&nd, dev_name, flags & MS_REC);
+		retval = do_loopback(&nd, dev_name, flags);
 	else if (flags & (MS_SHARED | MS_PRIVATE | MS_SLAVE | MS_UNBINDABLE))
 		retval = do_change_type(&nd, flags);
 	else if (flags & MS_MOVE)
Index: linux/include/linux/fs.h
===================================================================
--- linux.orig/include/linux/fs.h	2007-04-13 12:24:15.000000000 +0200
+++ linux/include/linux/fs.h	2007-04-13 13:03:42.000000000 +0200
@@ -123,6 +123,7 @@ extern int dir_notify_enable;
 #define MS_SLAVE	(1<<19)	/* change to slave */
 #define MS_SHARED	(1<<20)	/* change to shared */
 #define MS_RELATIME	(1<<21)	/* Update atime relative to mtime/ctime. */
+#define MS_SETUSER	(1<<22) /* set mnt_uid to current user */
 #define MS_ACTIVE	(1<<30)
 #define MS_NOUSER	(1<<31)
 
Index: linux/include/linux/mount.h
===================================================================
--- linux.orig/include/linux/mount.h	2007-04-13 12:24:15.000000000 +0200
+++ linux/include/linux/mount.h	2007-04-13 13:03:58.000000000 +0200
@@ -30,6 +30,7 @@ struct mnt_namespace;
 #define MNT_RELATIME	0x20
 
 #define MNT_SHRINKABLE	0x100
+#define MNT_USER	0x200
 
 #define MNT_SHARED	0x1000	/* if the vfsmount is a shared mount */
 #define MNT_UNBINDABLE	0x2000	/* if the vfsmount is a unbindable mount */
@@ -61,6 +62,8 @@ struct vfsmount {
 	atomic_t mnt_count;
 	int mnt_expiry_mark;		/* true if marked for expiry */
 	int mnt_pinned;
+
+	uid_t mnt_uid;			/* owner of the mount */
 };
 
 static inline struct vfsmount *mntget(struct vfsmount *mnt)
Index: linux/fs/pnode.h
===================================================================
--- linux.orig/fs/pnode.h	2007-04-13 12:24:15.000000000 +0200
+++ linux/fs/pnode.h	2007-04-13 12:25:52.000000000 +0200
@@ -22,6 +22,7 @@
 #define CL_COPY_ALL 		0x04
 #define CL_MAKE_SHARED 		0x08
 #define CL_PROPAGATION 		0x10
+#define CL_SETUSER		0x20
 
 static inline void set_mnt_shared(struct vfsmount *mnt)
 {

--
-
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