On Fri, Jan 8, 2021 at 12:33 AM Lokesh Gidra <lokeshgidra@xxxxxxxxxx> wrote:
>
> From: Daniel Colascione <dancol@xxxxxxxxxx>
>
> This change uses the anon_inodes and LSM infrastructure introduced in
> the previous patches to give SELinux the ability to control
> anonymous-inode files that are created using the new
> anon_inode_getfd_secure() function.
>
> A SELinux policy author detects and controls these anonymous inodes by
> adding a name-based type_transition rule that assigns a new security
> type to anonymous-inode files created in some domain. The name used
> for the name-based transition is the name associated with the
> anonymous inode for file listings --- e.g., "[userfaultfd]" or
> "[perf_event]".
>
> Example:
>
> type uffd_t;
> type_transition sysadm_t sysadm_t : anon_inode uffd_t "[userfaultfd]";
> allow sysadm_t uffd_t:anon_inode { create };
>
> (The next patch in this series is necessary for making userfaultfd
> support this new interface. The example above is just
> for exposition.)
>
> Signed-off-by: Daniel Colascione <dancol@xxxxxxxxxx>
> Signed-off-by: Lokesh Gidra <lokeshgidra@xxxxxxxxxx>
> ---
> security/selinux/hooks.c | 59 +++++++++++++++++++++++++++++
> security/selinux/include/classmap.h | 2 +
> 2 files changed, 61 insertions(+)
>
> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 644b17ec9e63..8b4e155b2930 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -2934,6 +2933,63 @@ static int selinux_inode_init_security(struct inode *inode, struct inode *dir,
> return 0;
> }
>
> +static int selinux_inode_init_security_anon(struct inode *inode,
> + const struct qstr *name,
> + const struct inode *context_inode)
> +{
> + const struct task_security_struct *tsec = selinux_cred(current_cred());
> + struct common_audit_data ad;
> + struct inode_security_struct *isec;
> + int rc;
> +
> + if (unlikely(!selinux_initialized(&selinux_state)))
> + return 0;
> +
> + isec = selinux_inode(inode);
> +
> + /*
> + * We only get here once per ephemeral inode. The inode has
> + * been initialized via inode_alloc_security but is otherwise
> + * untouched.
> + */
> + isec->initialized = LABEL_INITIALIZED;
> + isec->sclass = SECCLASS_ANON_INODE;
> +
> + if (context_inode) {
> + struct inode_security_struct *context_isec =
> + selinux_inode(context_inode);
> + if (context_isec->initialized != LABEL_INITIALIZED)
> + return -EACCES;
> + if (context_isec->sclass != SECCLASS_ANON_INODE) {
> + pr_err("SELinux: initializing anonymous inode with non-anonymous inode");
> + return -EACCES;
> + }
This would preclude using this facility for anonymous inodes created
by kvm and other use cases.
Don't do this.
> +
> + isec->sid = context_isec->sid;
> + } else {
> + rc = security_transition_sid(
> + &selinux_state, tsec->sid, tsec->sid,
> + isec->sclass, name, &isec->sid);
> + if (rc)
> + return rc;
> + }
> +
> + /*
> + * Now that we've initialized security, check whether we're
> + * allowed to actually create this type of anonymous inode.
> + */
> +
> + ad.type = LSM_AUDIT_DATA_INODE;
> + ad.u.inode = inode;
> +
> + return avc_has_perm(&selinux_state,
> + tsec->sid,
> + isec->sid,
> + isec->sclass,
> + ANON_INODE__CREATE,
FILE__CREATE is perfectly appropriate here, not that it makes any difference.
