Bug#770492: [RFC PATCH RESEND] vfs: Move security_inode_killpriv() after permission checks

[James Morris <jmorris@namei.org>]

On Sat, 17 Jan 2015, Ben Hutchings wrote:

> chown() and write() should clear all privilege attributes on
> a file - setuid, setgid, setcap and any other extended
> privilege attributes.
> 
> However, any attributes beyond setuid and setgid are managed by the
> LSM and not directly by the filesystem, so they cannot be set along
> with the other attributes.
> 
> Currently we call security_inode_killpriv() in notify_change(),
> but in case of a chown() this is too early - we have not called
> inode_change_ok() or made any filesystem-specific permission/sanity
> checks.
> 
> Add a new function setattr_killpriv() which calls
> security_inode_killpriv() if necessary, and change the setattr()
> implementation to call this in each filesystem that supports xattrs.
> This assumes that extended privilege attributes are always stored in
> xattrs.

It'd be useful to get some input from LSM module maintainers on this. 

e.g. doesn't SELinux already handle this via policy directives?


-- 
James Morris
<jmorris@namei.org>