[libvirt] [PATCH 1/4] Mount fresh instance of sysfs/selinux in LXC

[Daniel P. Berrange]

From: "Daniel P. Berrange" <berrange at redhat.com>

Currently to make sysfs readonly, we remount the existing
instance and then bind it readonly. Unfortunately this means
sysfs is still showing device objects wrt the host OS namespace.
We need it to reflect the container namespace, so we must mount
a completely new instance of it. Do the same for selinuxfs since
there is no benefit to bind mounting & this lets us simplify
the code.

* src/lxc/lxc_container.c: Mount fresh sysfs instance

Signed-off-by: Daniel P. Berrange <berrange at redhat.com>
---
 src/lxc/lxc_container.c |   32 +++++++++++---------------------
 1 file changed, 11 insertions(+), 21 deletions(-)

diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
index ca5696d..2076c04 100644
--- a/src/lxc/lxc_container.c
+++ b/src/lxc/lxc_container.c
@@ -423,12 +423,10 @@ err:
 
 
 static int lxcContainerMountBasicFS(virDomainDefPtr def,
-                                    const char *srcprefix,
                                     bool pivotRoot,
                                     virSecurityManagerPtr securityDriver)
 {
     const struct {
-        bool needPrefix;
         const char *src;
         const char *dst;
         const char *type;
@@ -441,20 +439,20 @@ static int lxcContainerMountBasicFS(virDomainDefPtr def,
          * mount point in the main OS becomes readonly too which is not what
          * we want. Hence some things have two entries here.
          */
-        { false, "proc", "/proc", "proc", NULL, MS_NOSUID|MS_NOEXEC|MS_NODEV },
-        { false, "/proc/sys", "/proc/sys", NULL, NULL, MS_BIND },
-        { false, "/proc/sys", "/proc/sys", NULL, NULL, MS_BIND|MS_REMOUNT|MS_RDONLY },
-        { true, "/sys", "/sys", NULL, NULL, MS_BIND },
-        { true, "/sys", "/sys", NULL, NULL, MS_BIND|MS_REMOUNT|MS_RDONLY },
+        { "proc", "/proc", "proc", NULL, MS_NOSUID|MS_NOEXEC|MS_NODEV },
+        { "/proc/sys", "/proc/sys", NULL, NULL, MS_BIND },
+        { "/proc/sys", "/proc/sys", NULL, NULL, MS_BIND|MS_REMOUNT|MS_RDONLY },
+        { "sysfs", "/sys", "sysfs", NULL, MS_NOSUID|MS_NOEXEC|MS_NODEV },
+        { "sysfs", "/sys", "sysfs", NULL, MS_BIND|MS_REMOUNT|MS_RDONLY },
 #if HAVE_SELINUX
-        { true, SELINUX_MOUNT, SELINUX_MOUNT, NULL, NULL, MS_BIND },
-        { true, SELINUX_MOUNT, SELINUX_MOUNT, NULL, NULL, MS_BIND|MS_REMOUNT|MS_RDONLY },
+        { SELINUX_MOUNT, SELINUX_MOUNT, "selinuxfs", NULL, MS_NOSUID|MS_NOEXEC|MS_NODEV },
+        { SELINUX_MOUNT, SELINUX_MOUNT, NULL, NULL, MS_BIND|MS_REMOUNT|MS_RDONLY },
 #endif
     };
     int i, rc = -1;
     char *opts = NULL;
 
-    VIR_DEBUG("Mounting basic filesystems %s pivotRoot=%d", NULLSTR(srcprefix), pivotRoot);
+    VIR_DEBUG("Mounting basic filesystems pivotRoot=%d", pivotRoot);
 
     for (i = 0 ; i < ARRAY_CARDINALITY(mnts) ; i++) {
         char *src = NULL;
@@ -470,15 +468,7 @@ static int lxcContainerMountBasicFS(virDomainDefPtr def,
             goto cleanup;
         }
 
-        if (mnts[i].needPrefix && srcprefix) {
-            if (virAsprintf(&src, "%s%s", srcprefix, mnts[i].src) < 0) {
-                virReportOOMError();
-                goto cleanup;
-            }
-            srcpath = src;
-        } else {
-            srcpath = mnts[i].src;
-        }
+        srcpath = mnts[i].src;
 
         /* Skip if mount doesn't exist in source */
         if ((srcpath[0] == '/') &&
@@ -1121,7 +1111,7 @@ static int lxcContainerSetupPivotRoot(virDomainDefPtr vmDef,
         return -1;
 
     /* Mounts the core /proc, /sys, etc filesystems */
-    if (lxcContainerMountBasicFS(vmDef, "/.oldroot", true, securityDriver) < 0)
+    if (lxcContainerMountBasicFS(vmDef, true, securityDriver) < 0)
         return -1;
 
     /* Mounts /dev/pts */
@@ -1166,7 +1156,7 @@ static int lxcContainerSetupExtraMounts(virDomainDefPtr vmDef,
         return -1;
 
     /* Mounts the core /proc, /sys, etc filesystems */
-    if (lxcContainerMountBasicFS(vmDef, NULL, false, securityDriver) < 0)
+    if (lxcContainerMountBasicFS(vmDef, false, securityDriver) < 0)
         return -1;
 
     VIR_DEBUG("Mounting completed");
-- 
1.7.10.1