[PATCH] c/r: restart to handle checkpoint images lacking {uts, ipc}-ns

[Oren Laadan <orenl@xxxxxxxxxxxxxxx>]

A checkpoint taken on a kernel without CONFIG_{IPC,UTS}_NS will leave
the corresponding objref field in the nsproxy header untouched, and
therefore it will remain zero.

This patch ensures that do_restore_ns() gracefully handles this by
borrowing from the nsproxy of the root-task.

Signed-off-by: Oren Laadan <orenl@xxxxxxxxxxxxxxx>
---
 kernel/nsproxy.c |   71 +++++++++++++++++++++++++++++------------------------
 1 files changed, 39 insertions(+), 32 deletions(-)

diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index b0e71f2..cfef7bc 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -312,54 +312,61 @@ static struct nsproxy *do_restore_ns(struct ckpt_ctx *ctx)
 	struct nsproxy *nsproxy = NULL;
 	struct uts_namespace *uts_ns;
 	struct ipc_namespace *ipc_ns;
+	struct mnt_namespace *mnt_ns;
+	struct net *net_ns;
 	int ret;
 
 	h = ckpt_read_obj_type(ctx, sizeof(*h), CKPT_HDR_NS);
 	if (IS_ERR(h))
 		return (struct nsproxy *) h;
 
-	ret = -EINVAL;
-	if (h->uts_objref <= 0 ||
-	    h->ipc_objref <= 0)
-		goto out;
-
-	uts_ns = ckpt_obj_fetch(ctx, h->uts_objref, CKPT_OBJ_UTS_NS);
+	if (h->uts_objref == 0)
+		uts_ns = ctx->root_nsproxy->uts_ns;
+	else
+		uts_ns = ckpt_obj_fetch(ctx, h->uts_objref, CKPT_OBJ_UTS_NS);
 	if (IS_ERR(uts_ns)) {
 		ret = PTR_ERR(uts_ns);
 		goto out;
 	}
-	ipc_ns = ckpt_obj_fetch(ctx, h->ipc_objref, CKPT_OBJ_IPC_NS);
+
+	if (h->ipc_objref == 0)
+		ipc_ns = ctx->root_nsproxy->ipc_ns;
+	else
+		ipc_ns = ckpt_obj_fetch(ctx, h->ipc_objref, CKPT_OBJ_IPC_NS);
 	if (IS_ERR(ipc_ns)) {
 		ret = PTR_ERR(ipc_ns);
 		goto out;
 	}
 
-#if defined(COFNIG_UTS_NS) || defined(CONFIG_IPC_NS)
-	ret = -ENOMEM;
-	nsproxy = create_nsproxy();
-	if (!nsproxy)
-		goto out;
+	mnt_ns = ctx->root_nsproxy->mnt_ns;
+	net_ns = ctx->root_nsproxy->net_ns;
+
+	if (uts_ns == current->nsproxy->uts_ns &&
+	    ipc_ns == current->nsproxy->ipc_ns &&
+	    mnt_ns == current->nsproxy->mnt_ns &&
+	    net_ns == current->nsproxy->net_ns) {
+		/* all xxx-ns are identical: reuse nsproxy */
+		nsproxy = current->nsproxy;
+		get_nsproxy(nsproxy);
+	} else {
+		ret = -ENOMEM;
+		nsproxy = create_nsproxy();
+		if (!nsproxy)
+			goto out;
+
+		get_uts_ns(uts_ns);
+		nsproxy->uts_ns = uts_ns;
+		get_ipc_ns(ipc_ns);
+		nsproxy->ipc_ns = ipc_ns;
+		get_mnt_ns(mnt_ns);
+		nsproxy->mnt_ns = mnt_ns;
+		get_net(net_ns);
+		nsproxy->net_ns = net_ns;
+
+		get_pid_ns(current->nsproxy->pid_ns);
+		nsproxy->pid_ns = current->nsproxy->pid_ns;
+	}
 
-	get_uts_ns(uts_ns);
-	nsproxy->uts_ns = uts_ns;
-	get_ipc_ns(ipc_ns);
-	nsproxy->ipc_ns = ipc_ns;
-
-	get_pid_ns(current->nsproxy->pid_ns);
-	nsproxy->pid_ns = current->nsproxy->pid_ns;
-	get_mnt_ns(current->nsproxy->mnt_ns);
-	nsproxy->mnt_ns = current->nsproxy->mnt_ns;
-	get_net(current->nsproxy->net_ns);
-	nsproxy->net_ns = current->nsproxy->net_ns;
-#else
-	nsproxy = current->nsproxy;
-	get_nsproxy(nsproxy);
-
-	BUG_ON(nsproxy->uts_ns != uts_ns);
-	BUG_ON(nsproxy->ipc_ns != ipc_ns);
-#endif
-
-	/* TODO: add more namespaces here */
 	ret = 0;
  out:
 	if (ret < 0)
-- 
1.6.3.3

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