File 15073504-CVE-2021-3631.patch of Package libvirt.22369

commit 15073504dbb624d3f6c911e85557019d3620fdb2
Author: Daniel P. Berrangé <berrange@redhat.com>
Date:   Mon Jun 28 13:09:04 2021 +0100

    security: fix SELinux label generation logic
    
    A process can access a file if the set of MCS categories
    for the file is equal-to *or* a subset-of, the set of
    MCS categories for the process.
    
    If there are two VMs:
    
      a) svirt_t:s0:c117
      b) svirt_t:s0:c117,c720
    
    Then VM (b) is able to access files labelled for VM (a).
    
    IOW, we must discard case where the categories are equal
    because that is a subset of many other valid category pairs.
    
    Fixes: https://gitlab.com/libvirt/libvirt/-/issues/153
    CVE-2021-3631
    Reviewed-by: Peter Krempa <pkrempa@redhat.com>
    Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

Index: libvirt-7.1.0/src/security/security_selinux.c
===================================================================
--- libvirt-7.1.0.orig/src/security/security_selinux.c
+++ libvirt-7.1.0/src/security/security_selinux.c
@@ -389,7 +389,15 @@ virSecuritySELinuxMCSFind(virSecurityMan
         VIR_DEBUG("Try cat %s:c%d,c%d", sens, c1 + catMin, c2 + catMin);
 
         if (c1 == c2) {
-            mcs = g_strdup_printf("%s:c%d", sens, catMin + c1);
+            /*
+             * A process can access a file if the set of MCS categories
+             * for the file is equal-to *or* a subset-of, the set of
+             * MCS categories for the process.
+             *
+             * IOW, we must discard case where the categories are equal
+             * because that is a subset of other category pairs.
+             */
+            continue;
         } else {
             if (c1 > c2) {
                 int t = c1;