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Subject[PATCH] fix SEM_UNDO with namespaces, take 2
Hi,

below is the second attempt to fix SEM_UNDO + unshare():
lookup_undo (in ipc/sem.c) is not namespace-aware, thus all entries in
sysvsem.undo_list must be from the same namespace.
The patch enforces that by detaching the current thread from
sysvsem.undo_list in switch_task_namespaces() if the ipc namespace is
changed.

The patch boots and passes simple sysvsem+unshare tests.

Signed-Off-By: Manfred Spraul <manfred@colorfullife.com>
diff --git a/ipc/sem.c b/ipc/sem.c
index 0b45a4d..35841bd 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1298,6 +1298,7 @@ void exit_sem(struct task_struct *tsk)
undo_list = tsk->sysvsem.undo_list;
if (!undo_list)
return;
+ tsk->sysvsem.undo_list = NULL;

if (!atomic_dec_and_test(&undo_list->refcnt))
return;
diff --git a/kernel/nsproxy.c b/kernel/nsproxy.c
index f5d332c..ddeb9d1 100644
--- a/kernel/nsproxy.c
+++ b/kernel/nsproxy.c
@@ -211,6 +211,18 @@ void switch_task_namespaces(struct task_struct *p, struct nsproxy *new)

might_sleep();

+ if ((p->nsproxy == NULL && new != NULL) ||
+ (p->nsproxy != NULL && new == NULL) ||
+ (p->nsproxy != NULL && new != NULL && p->nsproxy->ipc_ns != new->ipc_ns)) {
+ /* switching the IPC namespace is considered equivalent to sys_exit() wrt.
+ * to outstanding SEM_UNDO undos: After switching to the new IPC namespace,
+ * the semaphore arrays from the old namespace are not accessible anymore.
+ *
+ * Additionally, an implicit sys_unshare(CLONE_SYSVSEM) is performed.
+ */
+ exit_sem(p);
+ }
+
ns = p->nsproxy;

rcu_assign_pointer(p->nsproxy, new);
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