linux-kernel - Re: [PATCH 1/2] pipe: fix potential use-after-free in pipe

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Date:   Tue, 23 Nov 2021 09:09:42 +0800
From:   "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
To:     Matthew Wilcox <willy@...radead.org>
CC:     Alexander Viro <viro@...iv.linux.org.uk>,
        David Howells <dhowells@...hat.com>,
        <linux-fsdevel@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] pipe: fix potential use-after-free in pipe_read()



On 2021/11/15 21:05, Matthew Wilcox wrote:
> On Mon, Nov 15, 2021 at 02:13:44PM +0800, Leizhen (ThunderTown) wrote:
>>
>>
>> On 2021/11/15 12:25, Matthew Wilcox wrote:
>>> On Mon, Nov 15, 2021 at 11:57:20AM +0800, Zhen Lei wrote:
>>>>  			if (!buf->len) {
>>>> +				unsigned int __maybe_unused flags = buf->flags;
>>>
>>> Why __maybe_unused?
>>
>> It's used only if "#ifdef CONFIG_WATCH_QUEUE". Otherwise, a warning will be reported.
> 
> Better to turn the #ifdef into if (IS_ENABLED())

Hi, Matthew:
  Thank you for your advice. IS_ENABLED() is a good idea, but when I tried it, I found that
the macro 'PIPE_BUF_FLAG_LOSS' and the structure member 'note_loss' were also separated by
"ifdef CONFIG_WATCH_QUEUE", so this method is not suitable here.

#ifdef CONFIG_WATCH_QUEUE
#define PIPE_BUF_FLAG_LOSS     0x40    /* Message loss happened after this buffer */
#endif

@@ -62,9 +60,7 @@ struct pipe_inode_info {
        unsigned int tail;
        unsigned int max_usage;
        unsigned int ring_size;
#ifdef CONFIG_WATCH_QUEUE
        bool note_loss;
#endif



> .
>