Re: [patch 12/12] vfs: allow file truncations when both suid and write permissions set

[OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>]

Amerigo Wang <amwang@redhat.com> writes:

>> static int selinux_inode_setattr(struct dentry *dentry, struct iattr *iattr)
>> {
>> 	const struct cred *cred = current_cred();
>>
>> 	if (iattr->ia_valid & ATTR_FORCE)
>> 		return 0;
>>
>> 	if (iattr->ia_valid & (ATTR_MODE | ATTR_UID | ATTR_GID |
>> 			       ATTR_ATIME_SET | ATTR_MTIME_SET))
>> 		return dentry_has_perm(cred, NULL, dentry, FILE__SETATTR);
>>
>> 	return dentry_has_perm(cred, NULL, dentry, FILE__WRITE);
>> }
>>
>> I guess it's assuming the ia_valid doesn't have (ATTR_MODE | ATTR_SIZE),
>> but truncate() already does it, I don't know whether it's ok. 
>
> No, here we should only force ATTR_KILL_SUID and/or ATTR_KILL_SGID. 
> do_truncate() has ATTR_SIZE and ATTR_FILE.

I guess security module should do,

	ia_valid = iattr->ia_valid;
	if (!(ia_valid & ATTR_FORCE) && (ia_valid & ATTR_FORCE_MASK)) {
		err = dentry_has_perm(cred, NULL, dentry, FILE__SETATTR);
		if (err)
                	return err;
		ia_valid &= ~ATTR_FORCE_MASK;
	}
	if (ia_valid & ATTR_NOT_FORCE_MASK)
	 	err = dentry_has_perm(cred, NULL, dentry, FILE__WRITE);
	return err;

or something. Because do_truncate() already do (ATTR_MODE | ATTR_SIZE)
without ATTR_FORCE.

Thanks.
-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>