[PATCH] SELinux: retain ptracer SID across fork

This fixes a bug in SELinux to retain the ptracer SID (if any) across fork.
Otherwise, SELinux will always deny attempts by traced children to exec
domain-changing programs even if the policy would have allowed the tracer
to trace the new domains as well.
Signed-off-by: Stephen Smalley <sds@epoch.ncsc.mil>
Signed-off-by: James Morris <jmorris@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

security/selinux/hooks.c

@@ -2625,6 +2625,11 @@ static int selinux_task_alloc_security(struct task_struct *tsk)
 	tsec2->exec_sid = tsec1->exec_sid;
 	tsec2->create_sid = tsec1->create_sid;
 
+	/* Retain ptracer SID across fork, if any.
+	   This will be reset by the ptrace hook upon any
+	   subsequent ptrace_attach operations. */
+	tsec2->ptrace_sid = tsec1->ptrace_sid;
+
 	return 0;
 }