[PATCH] security: Return xattr name from security_dentry_init_security()

[Al Viro]

On Thu, Sep 30, 2021 at 02:59:10PM -0400, Vivek Goyal wrote:
> Right now security_dentry_init_security() only supports single security
> label and is used by SELinux only. There are two users of of this hook,
> namely ceph and nfs.
> 
> NFS does not care about xattr name. Ceph hardcodes the xattr name to
> security.selinux (XATTR_NAME_SELINUX).
> 
> I am making changes to fuse/virtiofs to send security label to virtiofsd
> and I need to send xattr name as well. I also hardcoded the name of
> xattr to security.selinux.
> 
> Stephen Smalley suggested that it probably is a good idea to modify
> security_dentry_init_security() to also return name of xattr so that
> we can avoid this hardcoding in the callers.
> 
> This patch adds a new parameter "const char **xattr_name" to
> security_dentry_init_security() and LSM puts the name of xattr
> too if caller asked for it (xattr_name != NULL).

Umm...  Why not return the damn thing on success and ERR_PTR(-E...)
on failure, instead of breeding extra arguments?