From 95a3540da9c81a5987be810e1d9a83640a366bd5 Mon Sep 17 00:00:00 2001
From: Oleg Nesterov <oleg@redhat.com>
Date: Thu, 2 Apr 2009 16:58:21 -0700
Subject: [PATCH] ptrace_detach: the wrong wakeup breaks the ERESTARTxxx logic
Another ancient bug. Consider this trivial test-case,
int main(void)
{
int pid = fork();
if (pid) {
ptrace(PTRACE_ATTACH, pid, NULL, NULL);
wait(NULL);
ptrace(PTRACE_DETACH, pid, NULL, NULL);
} else {
pause();
printf("WE HAVE A KERNEL BUG!!!\n");
}
return 0;
}
the child must not "escape" for sys_pause(), but it can and this was seen
in practice.
This is because ptrace_detach does:
if (!child->exit_state)
wake_up_process(child);
this wakeup can happen after this child has already restarted sys_pause(),
because it gets another wakeup from ptrace_untrace().
With or without this patch, perhaps sys_pause() needs a fix. But this
wakeup also breaks the SIGNAL_STOP_STOPPED logic in ptrace_untrace().
Remove this wakeup. The caller saw this task in TASK_TRACED state, and
unless it was SIGKILL'ed in between __ptrace_unlink()->ptrace_untrace()
should handle this case correctly. If it was SIGKILL'ed, we don't need to
wakup the dying tracee too.
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Jerome Marchand <jmarchan@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
kernel/ptrace.c | 4 ----
1 file changed, 4 deletions(-)
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index f5a9fa5aafa10..296e8105863af 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -301,11 +301,7 @@ int ptrace_detach(struct task_struct *child, unsigned int data)
*/
if (child->ptrace) {
child->exit_code = data;
-
dead = __ptrace_detach(current, child);
-
- if (!child->exit_state)
- wake_up_process(child);
}
write_unlock_irq(&tasklist_lock);
--
GitLab