From e30dbf35a1a9e86934272aeef803f91b36d8cbce Mon Sep 17 00:00:00 2001
From: Michal Privoznik <mprivozn@redhat.com>
Date: Fri, 28 Apr 2017 10:45:45 +0200
Subject: [PATCH] qemuDomainCreateDeviceRecursive: Don't try to create devices
 under preserved mount points

While the code allows devices to already be there (by some
miracle), we shouldn't try to create devices that don't belong to
us. For instance, we shouldn't try to create /dev/shm/file
because /dev/shm is a mount point that is preserved. Therefore if
a file is created there from an outside (e.g. by mgmt application
or some other daemon running on the system like vhostmd), it
exists in the qemu namespace too as the mount point is the same.
It's only /dev and /dev only that is different. The same
reasoning applies to all other preserved mount points.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Cedric Bosdonnat <cbosdonnat@suse.com>
---
 src/qemu/qemu_domain.c | 39 ++++++++++++++++++++++++++++++---------
 1 file changed, 30 insertions(+), 9 deletions(-)

diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
index 87c98ae00b..1e439848f7 100644
--- a/src/qemu/qemu_domain.c
+++ b/src/qemu/qemu_domain.c
@@ -7418,6 +7418,8 @@ qemuDomainGetPreservedMounts(virQEMUDriverConfigPtr cfg,
 
 struct qemuDomainCreateDeviceData {
     const char *path;     /* Path to temp new /dev location */
+    char * const *devMountsPath;
+    size_t ndevMountsPath;
 };
 
 
@@ -7471,17 +7473,34 @@ qemuDomainCreateDeviceRecursive(const char *device,
      * For now, lets hope callers play nice.
      */
     if (STRPREFIX(device, DEVPREFIX)) {
-        if (virAsprintf(&devicePath, "%s/%s",
-                        data->path, device + strlen(DEVPREFIX)) < 0)
-            goto cleanup;
+        size_t i;
 
-        if (virFileMakeParentPath(devicePath) < 0) {
-            virReportSystemError(errno,
-                                 _("Unable to create %s"),
-                                 devicePath);
-            goto cleanup;
+        for (i = 0; i < data->ndevMountsPath; i++) {
+            if (STREQ(data->devMountsPath[i], "/dev"))
+                continue;
+            if (STRPREFIX(device, data->devMountsPath[i]))
+                break;
+        }
+
+        if (i == data->ndevMountsPath) {
+            /* Okay, @device is in /dev but not in any mount point under /dev.
+             * Create it. */
+            if (virAsprintf(&devicePath, "%s/%s",
+                            data->path, device + strlen(DEVPREFIX)) < 0)
+                goto cleanup;
+
+            if (virFileMakeParentPath(devicePath) < 0) {
+                virReportSystemError(errno,
+                                     _("Unable to create %s"),
+                                     devicePath);
+                goto cleanup;
+            }
+            VIR_DEBUG("Creating dev %s", device);
+            create = true;
+        } else {
+            VIR_DEBUG("Skipping dev %s because of %s mount point",
+                      device, data->devMountsPath[i]);
         }
-        create = true;
     }
 
     if (isLink) {
@@ -8030,6 +8049,8 @@ qemuDomainBuildNamespace(virQEMUDriverConfigPtr cfg,
     }
 
     data.path = devPath;
+    data.devMountsPath = devMountsPath;
+    data.ndevMountsPath = ndevMountsPath;
 
     if (virProcessSetupPrivateMountNS() < 0)
         goto cleanup;
-- 
2.47.2