ptrace: ptrace_attach: check PF_KTHREAD + exit_state instead of ->mm
- Add PF_KTHREAD check to prevent attaching to the kernel thread
with a borrowed ->mm.
With or without this change we can race with daemonize() which
can set PF_KTHREAD or clear ->mm after ptrace_attach() does the
check, but this doesn't matter because reparent_to_kthreadd()
does ptrace_unlink().
- Kill "!task->mm" check. We don't really care about ->mm != NULL,
and the task can call exit_mm() right after we drop task_lock().
What we need is to make sure we can't attach after exit_notify(),
check task->exit_state != 0 instead.
Also, move the "already traced" check down for cosmetic reasons.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index f6d8b8c..9439bd3 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -172,6 +172,8 @@
audit_ptrace(task);
retval = -EPERM;
+ if (unlikely(task->flags & PF_KTHREAD))
+ goto out;
if (same_thread_group(task, current))
goto out;
@@ -182,8 +184,6 @@
retval = mutex_lock_interruptible(&task->cred_guard_mutex);
if (retval < 0)
goto out;
-
- retval = -EPERM;
repeat:
/*
* Nasty, nasty.
@@ -203,23 +203,24 @@
goto repeat;
}
- if (!task->mm)
- goto bad;
- /* the same process cannot be attached many times */
- if (task->ptrace & PT_PTRACED)
- goto bad;
retval = __ptrace_may_access(task, PTRACE_MODE_ATTACH);
if (retval)
goto bad;
- /* Go */
+ retval = -EPERM;
+ if (unlikely(task->exit_state))
+ goto bad;
+ if (task->ptrace & PT_PTRACED)
+ goto bad;
+
task->ptrace |= PT_PTRACED;
if (capable(CAP_SYS_PTRACE))
task->ptrace |= PT_PTRACE_CAP;
__ptrace_link(task, current);
-
send_sig_info(SIGSTOP, SEND_SIG_FORCED, task);
+
+ retval = 0;
bad:
write_unlock_irqrestore(&tasklist_lock, flags);
task_unlock(task);