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binderfs: prevent renaming the control dentry 

- 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>
This commit is contained in:
Christian Brauner 2019-01-21 11:48:03 +01:00 committed by Greg Kroah-Hartman
parent 7c4d08fc4d
commit e98e6fa186
1 changed files with 10 additions and 18 deletions
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28
drivers/android/binderfs.c
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@ -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);