Fix ptrace self-attach rule

[Linus Torvalds]

Before we did CLONE_THREAD, the way to check whether we were attaching
to ourselves was to just check "current == task", but with CLONE_THREAD
we should check that the thread group ID matches instead.

Signed-off-by: Linus Torvalds <torvalds@xxxxxxxx>
---
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 5b8dd98..b88d418 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -155,7 +155,7 @@ int ptrace_attach(struct task_struct *ta
 	retval = -EPERM;
 	if (task->pid <= 1)
 		goto bad;
-	if (task == current)
+	if (task->tgid == current->tgid)
 		goto bad;
 	/* the same process cannot be attached many times */
 	if (task->ptrace & PT_PTRACED)
-
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