[Devel] [PATCH][RFC] Cleanup in namespaces unsharing

[Pavel Emelianov]

Currently we have two funtions to copy the namespaces:
copy_namespaces() and unshare_nsproxy_namespaces(). The
second one checks for unsupported functionality with

#ifndef CONFIG_IPC_NS
	if (unshare_flags & CLONE_NEWIPC)
		return -EINVAL;
#endif

-like constructions, while the first one does not. One
of the side effects of this is that clone() with the
CLONE_NEWXXX set will return 0 if the kernel doesn't
support XXX namespaces thus confusing the user-level.

The proposal is to make these calls clean from the ifdefs
and move these checks into each namespaces' stubs. This
will make the code cleaner and (!) return -EINVAL from 
fork() in case the desired namespaces are not supported.

Did I miss something in the design or this patch worth merging?

Signed-off-by: Pavel Emelianov <xemul at openvz.org>

---

diff --git a/include/linux/ipc.h b/include/linux/ipc.h
index 7c8c6d8..b5aed71 100644
--- a/include/linux/ipc.h
+++ b/include/linux/ipc.h
@@ -100,6 +100,9 @@ extern struct ipc_namespace *copy_ipcs(u
 static inline struct ipc_namespace *copy_ipcs(unsigned long flags,
 						struct ipc_namespace *ns)
 {
+	if (flags & CLONE_NEWIPC)
+		ns = ERR_PTR(-EINVAL);
+
 	return ns;
 }
 #endif
diff --git a/include/linux/utsname.h b/include/linux/utsname.h
index f8d3b32..230706e 100644
--- a/include/linux/utsname.h
+++ b/include/linux/utsname.h
@@ -60,6 +60,9 @@ static inline void put_uts_ns(struct uts
 static inline struct uts_namespace *copy_utsname(int flags,
 						struct uts_namespace *ns)
 {
+	if (flags & CLONE_NEWUTS)
+		ns = ERR_PTR(-EINVAL);
+
 	return ns;
 }
 
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index 1bc4b55..ef26615 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -157,16 +157,6 @@ int unshare_nsproxy_namespaces(unsigned 
 	if (!(unshare_flags & (CLONE_NEWNS | CLONE_NEWUTS | CLONE_NEWIPC)))
 		return 0;
 
-#ifndef CONFIG_IPC_NS
-	if (unshare_flags & CLONE_NEWIPC)
-		return -EINVAL;
-#endif
-
-#ifndef CONFIG_UTS_NS
-	if (unshare_flags & CLONE_NEWUTS)
-		return -EINVAL;
-#endif
-
 	if (!capable(CAP_SYS_ADMIN))
 		return -EPERM;