Check if a task has existing children or co-threads and refuse to set
the container ID if either are present.  Failure to check this could
permit games where a child scratches its parent's back to work around
inheritance and double-setting policy.

Signed-off-by: Richard Guy Briggs <r...@redhat.com>
---
 kernel/auditsc.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 29c8482..a6b0a52 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -2087,6 +2087,10 @@ static int audit_set_containerid_perm(struct task_struct 
*task, u64 containerid)
        /* if we don't have caps, reject */
        if (!capable(CAP_AUDIT_CONTROL))
                return -EPERM;
+       /* if task has children or is not single-threaded, deny */
+       if (!list_empty(&task->children) ||
+           !(thread_group_leader(task) && thread_group_empty(task)))
+               return -EPERM;
        /* if containerid is unset, allow */
        if (!audit_containerid_set(task))
                return 0;
-- 
1.8.3.1

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