[Devel] [RFC][PATCH 2/2] add the user namespace to the unshare syscall [try #2]

[Cedric Le Goater]

This patch allows a process to unshare its user namespace through
the unshare() syscall.

Signed-off-by: Cedric Le Goater <clg at fr.ibm.com>
Cc: Andrew Morton <akpm at osdl.org>
Cc: Kirill Korotaev <dev at openvz.org>
Cc: Eric W. Biederman <ebiederm at xmission.com>
Cc: Herbert Poetzl <herbert at 13thfloor.at>
Cc: Serge E. Hallyn <serue at us.ibm.com>
Cc: Dave Hansen <haveblue at us.ibm.com>

---
 kernel/fork.c |   21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

Index: 2.6.18-rc4-mm3/kernel/fork.c
===================================================================
--- 2.6.18-rc4-mm3.orig/kernel/fork.c
+++ 2.6.18-rc4-mm3/kernel/fork.c
@@ -1603,6 +1603,7 @@ asmlinkage long sys_unshare(unsigned lon
 	struct nsproxy *new_nsproxy = NULL, *old_nsproxy = NULL;
 	struct uts_namespace *uts, *new_uts = NULL;
 	struct ipc_namespace *ipc, *new_ipc = NULL;
+	struct user_namespace *user, *new_user = NULL;

 	check_unshare_flags(&unshare_flags);

@@ -1610,7 +1611,7 @@ asmlinkage long sys_unshare(unsigned lon
 	err = -EINVAL;
 	if (unshare_flags & ~(CLONE_THREAD|CLONE_FS|CLONE_NEWNS|CLONE_SIGHAND|
 				CLONE_VM|CLONE_FILES|CLONE_SYSVSEM|
-				CLONE_NEWUTS|CLONE_NEWIPC))
+				CLONE_NEWUTS|CLONE_NEWIPC|CLONE_NEWUSER))
 		goto bad_unshare_out;

 	if ((err = unshare_thread(unshare_flags)))
@@ -1631,18 +1632,20 @@ asmlinkage long sys_unshare(unsigned lon
 		goto bad_unshare_cleanup_semundo;
 	if ((err = unshare_ipcs(unshare_flags, &new_ipc)))
 		goto bad_unshare_cleanup_uts;
+	if ((err = unshare_user_ns(unshare_flags, &new_user)))
+		goto bad_unshare_cleanup_ipc;

-	if (new_ns || new_uts || new_ipc) {
+	if (new_ns || new_uts || new_ipc || new_user) {
 		old_nsproxy = current->nsproxy;
 		new_nsproxy = dup_namespaces(old_nsproxy);
 		if (!new_nsproxy) {
 			err = -ENOMEM;
-			goto bad_unshare_cleanup_ipc;
+			goto bad_unshare_cleanup_user;
 		}
 	}

 	if (new_fs || new_ns || new_sigh || new_mm || new_fd || new_ulist ||
-				new_uts || new_ipc) {
+				new_uts || new_ipc || new_user) {

 		task_lock(current);

@@ -1696,12 +1699,22 @@ asmlinkage long sys_unshare(unsigned lon
 			new_ipc = ipc;
 		}

+		if (new_user) {
+			user = current->nsproxy->user_ns;
+			current->nsproxy->user_ns = new_user;
+			new_user = user;
+		}
+
 		task_unlock(current);
 	}

 	if (new_nsproxy)
 		put_nsproxy(new_nsproxy);

+bad_unshare_cleanup_user:
+	if (new_user)
+		put_user_ns(new_user);
+
 bad_unshare_cleanup_ipc:
 	if (new_ipc)
 		put_ipc_ns(new_ipc);
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