[RH7,v2] ve: Reorder ve->ve_ns assignment in ve_grab_context()

Submitted by Kirill Tkhai on Oct. 30, 2020, 8:29 a.m.

Details

Message ID 160404648208.928964.15951786654227036299.stgit@localhost.localdomain
State New
Series "ve: Reorder ve->ve_ns assignment in ve_grab_context()"
Headers show

Commit Message

Kirill Tkhai Oct. 30, 2020, 8:29 a.m. 
This function must provide guarantees for readers, that
ve_ns != NULL under rcu_read_lock means the rest of context
(say, ve->init_task) is table.

But now order is wrong, and it does not guarantee that. Fix it.

v2: Use local variable for ve_ns, otherwise net_ns write results
in NULL pointer derefence.

Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
 kernel/ve/ve.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

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diff --git a/kernel/ve/ve.c b/kernel/ve/ve.c
index db26cbd41d3f..cfc3039bb85b 100644
--- a/kernel/ve/ve.c
+++ b/kernel/ve/ve.c
@@ -579,15 +579,18 @@  static void ve_stop_kthread(struct ve_struct *ve)
 static void ve_grab_context(struct ve_struct *ve)
 {
 	struct task_struct *tsk = current;
+	struct nsproxy *ve_ns;
 
 	get_task_struct(tsk);
 	ve->init_task = tsk;
 	ve->root_css_set = tsk->cgroups;
 	get_css_set(ve->root_css_set);
 	ve->init_cred = (struct cred *)get_current_cred();
-	rcu_assign_pointer(ve->ve_ns, get_nsproxy(tsk->nsproxy));
-	ve->ve_netns =  get_net(ve->ve_ns->net_ns);
+	ve_ns = get_nsproxy(tsk->nsproxy);
+	ve->ve_netns =  get_net(ve_ns->net_ns);
 	synchronize_rcu();
+
+	rcu_assign_pointer(ve->ve_ns, ve_ns);
 }
 
 static void ve_drop_context(struct ve_struct *ve)