linux-kernel - Re: [PATCH] fs: btrfs: Fix a possible null-pointer dereference in insert_inline

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Message-ID: <1b708c0d-8ea1-3898-0340-9cbce1fc2602@gmx.com>
Date:   Wed, 24 Jul 2019 10:57:24 +0800
From:   Qu Wenruo <quwenruo.btrfs@....com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>, clm@...com,
        josef@...icpanda.com, dsterba@...e.com
Cc:     linux-btrfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: btrfs: Fix a possible null-pointer dereference in
 insert_inline_extent()



On 2019/7/24 上午10:33, Jia-Ju Bai wrote:
> 
> 
> On 2019/7/24 10:21, Qu Wenruo wrote:
>>
>> On 2019/7/24 上午10:11, Jia-Ju Bai wrote:
>>> In insert_inline_extent(), there is an if statement on line 181 to check
>>> whether compressed_pages is NULL:
>>>      if (compressed_size && compressed_pages)
>>>
>>> When compressed_pages is NULL, compressed_pages is used on line 215:
>>>      cpage = compressed_pages[i];
>>>
>>> Thus, a possible null-pointer dereference may occur.
>>>
>>> To fix this possible bug, compressed_pages is checked on line 214.
>> This can only be hit with compressed_size > 0 and compressed_pages !=
>> NULL.
>>
>> It would be better to have an extra ASSERT() to warn developers about
>> the impossible case.
> 
> Thanks for the reply :)
> So I should add ASSERT(compressed_size > 0 & compressed_pages) at the
> beginning of the function, and remove "if (compressed_size &&
> compressed_pages)"?

My suggestion is, ASSERT((compressed_size >0 && compressed_pages) ||
(compressed_size == 0 && !compressed_pages))

And keeps the original checks.

Anyway, just a suggestion.

Thanks,
Qu

> 
> 
> Best wishes,
> Jia-Ju Bai



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