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From 0f7c8a271f07b3f9aff07dd814d7bec80ddac362 Mon Sep 17 00:00:00 2001
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Message-Id: <0f7c8a271f07b3f9aff07dd814d7bec80ddac362@dist-git>
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From: =?UTF-8?q?Daniel=20P=2E=20Berrang=C3=A9?= <berrange@redhat.com>
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Date: Wed, 28 Jul 2021 14:59:00 +0200
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Subject: [PATCH] security: fix SELinux label generation logic
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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A process can access a file if the set of MCS categories
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for the file is equal-to *or* a subset-of, the set of
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MCS categories for the process.
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If there are two VMs:
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a) svirt_t:s0:c117
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b) svirt_t:s0:c117,c720
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Then VM (b) is able to access files labelled for VM (a).
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IOW, we must discard case where the categories are equal
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because that is a subset of many other valid category pairs.
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Fixes: https://gitlab.com/libvirt/libvirt/-/issues/153
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CVE-2021-3631
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Reviewed-by: Peter Krempa <pkrempa@redhat.com>
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Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
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(cherry picked from commit 15073504dbb624d3f6c911e85557019d3620fdb2)
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Message-Id: <38c6a7b570b8eb2114d9f1ff0c84a8346e01472f.1627476632.git.pkrempa@redhat.com>
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Reviewed-by: Ján Tomko <jtomko@redhat.com>
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---
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src/security/security_selinux.c | 10 +++++++++-
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1 file changed, 9 insertions(+), 1 deletion(-)
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diff --git a/src/security/security_selinux.c b/src/security/security_selinux.c
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index 985c7eda1a..93fae831ca 100644
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--- a/src/security/security_selinux.c
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+++ b/src/security/security_selinux.c
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@@ -391,7 +391,15 @@ virSecuritySELinuxMCSFind(virSecurityManagerPtr mgr,
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VIR_DEBUG("Try cat %s:c%d,c%d", sens, c1 + catMin, c2 + catMin);
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if (c1 == c2) {
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- mcs = g_strdup_printf("%s:c%d", sens, catMin + c1);
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+ /*
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+ * A process can access a file if the set of MCS categories
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+ * for the file is equal-to *or* a subset-of, the set of
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+ * MCS categories for the process.
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+ *
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+ * IOW, we must discard case where the categories are equal
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+ * because that is a subset of other category pairs.
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+ */
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+ continue;
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} else {
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if (c1 > c2) {
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int t = c1;
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--
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2.32.0
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