ovl: don't allow writing ioctl on lower layer

[sfrench/cifs-2.6.git] / fs / namespace.c

diff --git a/fs/namespace.c b/fs/namespace.c
index 81f934b5d5718665cbfe6c3c44d3bdb716bc6711..df0f7521979a211eee70ae6a0e848d88bb1c65c9 100644 (file)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -431,13 +431,18 @@ int __mnt_want_write_file(struct file *file)
 }
 
 /**
- * mnt_want_write_file - get write access to a file's mount
+ * mnt_want_write_file_path - get write access to a file's mount
  * @file: the file who's mount on which to take a write
  *
  * This is like mnt_want_write, but it takes a file and can
  * do some optimisations if the file is open for write already
+ *
+ * Called by the vfs for cases when we have an open file at hand, but will do an
+ * inode operation on it (important distinction for files opened on overlayfs,
+ * since the file operations will come from the real underlying file, while
+ * inode operations come from the overlay).
  */
-int mnt_want_write_file(struct file *file)
+int mnt_want_write_file_path(struct file *file)
 {
        int ret;
 
@@ -447,6 +452,53 @@ int mnt_want_write_file(struct file *file)
                sb_end_write(file->f_path.mnt->mnt_sb);
        return ret;
 }
+
+static inline int may_write_real(struct file *file)
+{
+       struct dentry *dentry = file->f_path.dentry;
+       struct dentry *upperdentry;
+
+       /* Writable file? */
+       if (file->f_mode & FMODE_WRITER)
+               return 0;
+
+       /* Not overlayfs? */
+       if (likely(!(dentry->d_flags & DCACHE_OP_REAL)))
+               return 0;
+
+       /* File refers to upper, writable layer? */
+       upperdentry = d_real(dentry, NULL, 0, D_REAL_UPPER);
+       if (upperdentry && file_inode(file) == d_inode(upperdentry))
+               return 0;
+
+       /* Lower layer: can't write to real file, sorry... */
+       return -EPERM;
+}
+
+/**
+ * mnt_want_write_file - get write access to a file's mount
+ * @file: the file who's mount on which to take a write
+ *
+ * This is like mnt_want_write, but it takes a file and can
+ * do some optimisations if the file is open for write already
+ *
+ * Mostly called by filesystems from their ioctl operation before performing
+ * modification.  On overlayfs this needs to check if the file is on a read-only
+ * lower layer and deny access in that case.
+ */
+int mnt_want_write_file(struct file *file)
+{
+       int ret;
+
+       ret = may_write_real(file);
+       if (!ret) {
+               sb_start_write(file_inode(file)->i_sb);
+               ret = __mnt_want_write_file(file);
+               if (ret)
+                       sb_end_write(file_inode(file)->i_sb);
+       }
+       return ret;
+}
 EXPORT_SYMBOL_GPL(mnt_want_write_file);
 
 /**
@@ -484,10 +536,16 @@ void __mnt_drop_write_file(struct file *file)
        __mnt_drop_write(file->f_path.mnt);
 }
 
-void mnt_drop_write_file(struct file *file)
+void mnt_drop_write_file_path(struct file *file)
 {
        mnt_drop_write(file->f_path.mnt);
 }
+
+void mnt_drop_write_file(struct file *file)
+{
+       __mnt_drop_write(file->f_path.mnt);
+       sb_end_write(file_inode(file)->i_sb);
+}
 EXPORT_SYMBOL(mnt_drop_write_file);
 
 static int mnt_make_readonly(struct mount *mnt)
@@ -1238,65 +1296,6 @@ struct vfsmount *mnt_clone_internal(const struct path *path)
        return &p->mnt;
 }
 
-static inline void mangle(struct seq_file *m, const char *s)
-{
-       seq_escape(m, s, " \t\n\\");
-}
-
-/*
- * Simple .show_options callback for filesystems which don't want to
- * implement more complex mount option showing.
- *
- * See also save_mount_options().
- */
-int generic_show_options(struct seq_file *m, struct dentry *root)
-{
-       const char *options;
-
-       rcu_read_lock();
-       options = rcu_dereference(root->d_sb->s_options);
-
-       if (options != NULL && options[0]) {
-               seq_putc(m, ',');
-               mangle(m, options);
-       }
-       rcu_read_unlock();
-
-       return 0;
-}
-EXPORT_SYMBOL(generic_show_options);
-
-/*
- * If filesystem uses generic_show_options(), this function should be
- * called from the fill_super() callback.
- *
- * The .remount_fs callback usually needs to be handled in a special
- * way, to make sure, that previous options are not overwritten if the
- * remount fails.
- *
- * Also note, that if the filesystem's .remount_fs function doesn't
- * reset all options to their default value, but changes only newly
- * given options, then the displayed options will not reflect reality
- * any more.
- */
-void save_mount_options(struct super_block *sb, char *options)
-{
-       BUG_ON(sb->s_options);
-       rcu_assign_pointer(sb->s_options, kstrdup(options, GFP_KERNEL));
-}
-EXPORT_SYMBOL(save_mount_options);
-
-void replace_mount_options(struct super_block *sb, char *options)
-{
-       char *old = sb->s_options;
-       rcu_assign_pointer(sb->s_options, options);
-       if (old) {
-               synchronize_rcu();
-               kfree(old);
-       }
-}
-EXPORT_SYMBOL(replace_mount_options);
-
 #ifdef CONFIG_PROC_FS
 /* iterator; we want it to have access to namespace_sem, thus here... */
 static void *m_start(struct seq_file *m, loff_t *pos)
@@ -1657,7 +1656,7 @@ out_unlock:
        namespace_unlock();
 }
 
-/* 
+/*
  * Is the caller allowed to modify his namespace?
  */
 static inline bool may_mount(void)
@@ -2211,7 +2210,7 @@ static int do_loopback(struct path *path, const char *old_name,
 
        err = -EINVAL;
        if (mnt_ns_loop(old_path.dentry))
-               goto out; 
+               goto out;
 
        mp = lock_mount(path);
        err = PTR_ERR(mp);