Messages in this thread Patch in this message | | | From | Thomas Gleixner <> | Subject | Re: [PATCH] signal: Prevent sigqueue caching after task got released | Date | Tue, 22 Jun 2021 09:59:20 +0200 |
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On Tue, Jun 22 2021 at 08:34, Oleg Nesterov wrote: > On 06/22, Thomas Gleixner wrote: > > I guess you mean the race with exit_notify() ? Could you spell please?
Yes let me rephrase that.
> I am just curious how exactly this problem was found.
I was looking at that syzbot report
https://lore.kernel.org/r/000000000000148b4b05c419cbbb@google.com
and analyzed it how this ends up leaking memory.
> This doesn't really matter, because damn yes, a task T can call > release_task(another_task)->sigqueue_cache_or_free() after > exit_task_sigqueue_cache(T) was already called. For example, a last non-leader > thread exits and reaps a zombie leader. > > Somehow I thought that exit_task_sigqueue_cache() at the end of __exit_signal() > should fix this problem, but this is obviously wrong. > > >> @@ -463,13 +469,18 @@ void exit_task_sigqueue_cache(struct tas >> struct sigqueue *q = tsk->sigqueue_cache; >> >> if (q) { >> - tsk->sigqueue_cache = NULL; >> /* >> * Hand it back to the cache as the task might >> * be self reaping which would leak the object. >> */ >> kmem_cache_free(sigqueue_cachep, q); >> } >> + >> + /* >> + * Set an error pointer to ensure that @tsk will not cache a >> + * sigqueue when it is reaping it's child tasks >> + */ >> + tsk->sigqueue_cache = ERR_PTR(-1); >> } > > > Reviewed-by: Oleg Nesterov <oleg@redhat.com>
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