linux-kernel - Re: [PATCH v2] ext4: fix a NULL pointer when validating an inode bitmap

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Message-ID: <f898b4d4-f1b2-ffc6-4859-39cc99459cce@huawei.com>
Date:   Thu, 1 Dec 2022 14:20:09 +0800
From:   Baokun Li <libaokun1@...wei.com>
To:     Theodore Ts'o <tytso@....edu>
CC:     Luís Henriques <lhenriques@...e.de>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        <linux-ext4@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <stable@...r.kernel.org>
Subject: Re: [PATCH v2] ext4: fix a NULL pointer when validating an inode
 bitmap

On 2022/12/1 12:32, Theodore Ts'o wrote:
> On Wed, Nov 30, 2022 at 11:20:11AM +0800, Baokun Li wrote:
>>> If we can protect against the problem by adding a check that has other
>>> value as well (such as making usre that when ext4_iget fetches a
>>> special inode, we enforce that i_links_couint must be > 0), maybe
>>> that's worth it.
>> Yes, but some special inodes allow i_links_couint to be zero,
>> such as the uninitialized boot load inode.
> That's a good point; but the only time when a special inode can
> validly have a zero i_links_count is when it has no blocks associated
> to it.  Otherwise, when the file system releases the inode using
> iput() when the file system is unmounted, all of the blocks will get
> released when the inode is evicted.  So we can have ext4_iget() allow
> fetching an inode if i_blocks[] is zeros.  But if it has any blocks
> and i_links_count is non-zero, something must be terribly wrong with
> that inode.
>
> Cheers,
>
> 					- Ted
>
Totally agree! That sounds good!

-- 
With Best Regards,
Baokun Li
.