From 9acf4c64dd4560bd268006d7356c7455fab7e5b1 Mon Sep 17 00:00:00 2001
From: Changqing Li <changqing.li@windriver.com>
Date: Thu, 6 Sep 2018 14:52:12 +0800
Subject: [PATCH] seccomp: set the seccomp filter to all threads
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When using "-seccomp on", the seccomp policy is only applied to the
main thread, the vcpu worker thread and other worker threads created
after seccomp policy is applied; the seccomp policy is not applied to
e.g. the RCU thread because it is created before the seccomp policy is
applied and SECCOMP_FILTER_FLAG_TSYNC isn't used.

This can be verified with
for task in /proc/`pidof qemu`/task/*; do cat $task/status | grep Secc ; done
Seccomp:	2
Seccomp:	0
Seccomp:	0
Seccomp:	2
Seccomp:	2
Seccomp:	2

Starting with libseccomp 2.2.0 and kernel >= 3.17, we can use
seccomp_attr_set(ctx, > SCMP_FLTATR_CTL_TSYNC, 1) to update the policy
on all threads.

libseccomp requirement was bumped to 2.2.0 in previous patch.
libseccomp should fail to set the filter if it can't honour
SCMP_FLTATR_CTL_TSYNC (untested), and thus -sandbox will now fail on
kernel < 3.17.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Acked-by: Eduardo Otubo <otubo@redhat.com>

Upstream-Status: Backport[https://github.com/qemu/qemu/commit/
70dfabeaa79ba4d7a3b699abe1a047c8012db114#diff-18106d3b47a2d249f9d41e772b7db22d]

CVE: CVE-2018-15746

Signed-off-by: Changqing Li <changqing.li@windriver.com>
---
 qemu-seccomp.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/qemu-seccomp.c b/qemu-seccomp.c
index 9cd8eb9..ba5500a 100644
--- a/qemu-seccomp.c
+++ b/qemu-seccomp.c
@@ -120,6 +120,11 @@ static int seccomp_start(uint32_t seccomp_opts)
         goto seccomp_return;
     }
 
+    rc = seccomp_attr_set(ctx, SCMP_FLTATR_CTL_TSYNC, 1);
+    if (rc != 0) {
+        goto seccomp_return;
+    }
+
     for (i = 0; i < ARRAY_SIZE(blacklist); i++) {
         if (!(seccomp_opts & blacklist[i].set)) {
             continue;
-- 
2.7.4