selinux: fix mounting of cgroup2 under older policies

BugLink: https://bugs.launchpad.net/bugs/1836802
commit 7bb185edb0306bb90029a5fa6b9cff900ffdbf4b upstream.

commit 901ef845fa2469c ("selinux: allow per-file labeling for cgroupfs")
broke mounting of cgroup2 under older SELinux policies which lacked
a genfscon rule for cgroup2.  This prevents mounting of cgroup2 even
when SELinux is permissive.

Change the handling when there is no genfscon rule in policy to
just mark the inode unlabeled and not return an error to the caller.
This permits mounting and access if allowed by policy, e.g. to
unconfined domains.

I also considered changing the behavior of security_genfs_sid() to
never return -ENOENT, but the current behavior is relied upon by
other callers to perform caller-specific handling.

Fixes: 901ef845fa2469c ("selinux: allow per-file labeling for cgroupfs")
CC: <stable@vger.kernel.org>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Reported-by: Waiman Long <longman@redhat.com>
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
Tested-by: Waiman Long <longman@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index b6e4029021ac93e08ca6b246f0caad35f5a7161f..4a7fea3061df0ee205193be58e06c823343f45dc 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1424,6 +1424,11 @@ static int selinux_genfs_get_sid(struct dentry *dentry,
                        }
                }
                rc = security_genfs_sid(sb->s_type->name, path, tclass, sid);
+               if (rc == -ENOENT) {
+                       /* No match in policy, mark as unlabeled. */
+                       *sid = SECINITSID_UNLABELED;
+                       rc = 0;
+               }
        }
        free_page((unsigned long)buffer);
        return rc;