[PATCH]lxc: mount dir as readonly if ownership couldn't be known

[Chen Hanxiao <chenhanxiao@xxxxxxxxxxxxxx>]

From: Chen Hanxiao <chenhanxiao@xxxxxxxxxxxxxx>

We bind mount some dir from host to guest.
With userns enabled, if we couldn't know
the dir's ownership, it's better to
mount them as readonly.

Signed-off-by: Chen Hanxiao <chenhanxiao@xxxxxxxxxxxxxx>
---
 src/lxc/lxc_container.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
index 255c711..f3f0c15 100644
--- a/src/lxc/lxc_container.c
+++ b/src/lxc/lxc_container.c
@@ -96,6 +96,8 @@
 typedef char lxc_message_t;
 #define LXC_CONTINUE_MSG 'c'
 
+#define OVERFLOWUID 65534
+
 typedef struct __lxc_child_argv lxc_child_argv_t;
 struct __lxc_child_argv {
     virDomainDefPtr config;
@@ -1067,12 +1069,22 @@ static int lxcContainerMountFSBind(virDomainFSDefPtr fs,
     char *src = NULL;
     int ret = -1;
     struct stat st;
+    bool readonly = false;
 
     VIR_DEBUG("src=%s dst=%s", fs->src, fs->dst);
 
     if (virAsprintf(&src, "%s%s", srcprefix, fs->src) < 0)
         goto cleanup;
 
+    if (stat(src, &st) < 0) {
+        virReportSystemError(errno, _("Unable to stat bind source %s"),
+                             src);
+        goto cleanup;
+    } else {
+        if (OVERFLOWUID == st.st_uid || OVERFLOWUID == st.st_gid)
+            readonly = true;
+    }
+
     if (stat(fs->dst, &st) < 0) {
         if (errno != ENOENT) {
             virReportSystemError(errno, _("Unable to stat bind target %s"),
@@ -1119,7 +1131,7 @@ static int lxcContainerMountFSBind(virDomainFSDefPtr fs,
         goto cleanup;
     }
 
-    if (fs->readonly) {
+    if (fs->readonly || readonly) {
         VIR_DEBUG("Binding %s readonly", fs->dst);
         if (mount(src, fs->dst, NULL, MS_BIND|MS_REMOUNT|MS_RDONLY, NULL) < 0) {
             virReportSystemError(errno,
-- 
1.8.2.1

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