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security: fix SELinux label generation logic

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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>
This commit is contained in:
Daniel P. Berrangé 2021-06-28 13:09:04 +01:00
parent f63397de61
commit 15073504db
1 changed files with 9 additions and 1 deletions
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10
src/security/security_selinux.c
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@ -383,7 +383,15 @@ virSecuritySELinuxMCSFind(virSecurityManager *mgr,
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;