[PATCH 3/9] vfs: fix per mount read-write

[Miklos Szeredi <miklos@szeredi.hu>]

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From: Miklos Szeredi <mszeredi@suse.cz>

Don't allow remounting the vfsmount read-write if the superblock is
read-only.  Return -EROFS in this case.

Rename __mnt_unmake_readonly() to mnt_make_writable() to match
mnt_make_readonly().

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---
 fs/namespace.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

Index: linux-2.6/fs/namespace.c
===================================================================
--- linux-2.6.orig/fs/namespace.c	2010-09-30 16:53:30.000000000 +0200
+++ linux-2.6/fs/namespace.c	2010-09-30 16:57:47.000000000 +0200
@@ -399,11 +399,18 @@ static int mnt_make_readonly(struct vfsm
 	return ret;
 }
 
-static void __mnt_unmake_readonly(struct vfsmount *mnt)
+static int mnt_make_writable(struct vfsmount *mnt)
 {
+	int err = 0;
+
 	br_write_lock(vfsmount_lock);
-	mnt->mnt_flags &= ~MNT_READONLY;
+	if (mnt->mnt_sb->s_flags & MS_RDONLY)
+		err = -EROFS;
+	else
+		mnt->mnt_flags &= ~MNT_READONLY;
 	br_write_unlock(vfsmount_lock);
+
+	return err;
 }
 
 void simple_set_mnt(struct vfsmount *mnt, struct super_block *sb)
@@ -1600,7 +1607,7 @@ static int change_mount_flags(struct vfs
 	if (readonly_request)
 		error = mnt_make_readonly(mnt);
 	else
-		__mnt_unmake_readonly(mnt);
+		error = mnt_make_writable(mnt);
 	return error;
 }
 

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