binderfs: prevent renaming the control dentry (e98e6fa1) · Commits · 戴 / test

- make binderfs control dentry immutable: We don't allow to unlink it since it is crucial for binderfs to be useable but if we allow to rename it we make the unlink trivial to bypass. So prevent renaming too and simply treat the control dentry as immutable. - add is_binderfs_control_device() helper: Take the opportunity and turn the check for the control dentry into a separate helper is_binderfs_control_device() since it's now used in two places. - simplify binderfs_rename(): Instead of hand-rolling our custom version of simple_rename() just dumb the whole function down to first check whether we're trying to rename the control dentry. If we do EPERM the caller and if not call simple_rename(). Suggested-by:

Al Viro <viro@zeniv.linux.org.uk> Signed-off-by:

Christian Brauner <christian@brauner.io> Signed-off-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/android/binderfs.c

+10 −18

Original line number	Diff line number	Diff line
		@@ -346,34 +346,26 @@ static const struct super_operations binderfs_super_ops = {
		.statfs = simple_statfs,
		};

		static inline bool is_binderfs_control_device(const struct dentry *dentry)
		{
		struct binderfs_info *info = dentry->d_sb->s_fs_info;
		return info->control_dentry == dentry;
		}

		static int binderfs_rename(struct inode old_dir, struct dentry old_dentry,
		struct inode new_dir, struct dentry new_dentry,
		unsigned int flags)
		{
		struct inode *inode = d_inode(old_dentry);

		/* binderfs doesn't support directories. */
		if (d_is_dir(old_dentry))
		if (is_binderfs_control_device(old_dentry) \|\|
		is_binderfs_control_device(new_dentry))
		return -EPERM;

		if (flags & ~RENAME_NOREPLACE)
		return -EINVAL;

		if (!simple_empty(new_dentry))
		return -ENOTEMPTY;

		if (d_really_is_positive(new_dentry))
		simple_unlink(new_dir, new_dentry);

		old_dir->i_ctime = old_dir->i_mtime = new_dir->i_ctime =
		new_dir->i_mtime = inode->i_ctime = current_time(old_dir);

		return 0;
		return simple_rename(old_dir, old_dentry, new_dir, new_dentry, flags);
		}

		static int binderfs_unlink(struct inode dir, struct dentry dentry)
		{
		if (BINDERFS_I(dir)->control_dentry == dentry)
		if (is_binderfs_control_device(dentry))
		return -EPERM;

		return simple_unlink(dir, dentry);

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