Re: [PATCH] pipe: fix potential use-after-free in pipe_read()

["Leizhen (ThunderTown)" <thunder.leizhen@huawei.com>]

On 2022/11/25 14:33, Al Viro wrote:
> On Thu, Nov 17, 2022 at 07:53:23PM +0800, Zhen Lei wrote:
>> Accessing buf->flags after pipe_buf_release(pipe, buf) is unsafe, because
>> the 'buf' memory maybe freed.
> 
> Huh?  What are you talking about?
>                         struct pipe_buffer *buf = &pipe->bufs[tail & mask];
> To free *buf you would need to free the entire damn array, which is
> obviously not going to be possible here; if you are talking about reuse
> of *buf - that's controlled by pipe->tail, and we do not assign it until
> later.
> 
> Fetching any fields of *buf is safe; what can get freed is buf->page, not
> buf itself.  So that buf->flags access is fine.

Right. Thank you for explaining clearly. Sorry, I misunderstood in the
course of learning.

> 
> .
> 

-- 
Regards,
  Zhen Lei