linux-kernel - Re: [BUG] fs: f2fs: Possible null-pointer dereferences in update_general

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Message-ID: <2d66cd56-eccf-9086-c5db-118acce717a6@huawei.com>
Date:   Fri, 26 Jul 2019 11:19:41 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jia-Ju Bai <baijiaju1990@...il.com>, <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] fs: f2fs: Possible null-pointer dereferences in
 update_general_status()

Hi Jiaju,

Thanks for the report, I checked the code, and found it doesn't need to check
SM_I(sbi) pointer, this is because in fill_super() and put_super(), we will call
f2fs_destroy_stats() in prior to f2fs_destroy_segment_manager(), so if current
sbi can still be visited in global stat list, SM_I(sbi) should be released yet.
So anyway, let's remove unneeded check in line 70/78. :)

Thanks,

On 2019/7/25 17:49, Jia-Ju Bai wrote:
> In update_general_status(), there are two if statements to
> check whether SM_I(sbi) is NULL:
> LINE 70:     if (SM_I(sbi) && SM_I(sbi)->fcc_info)
> LINE 78:     if (SM_I(sbi) && SM_I(sbi)->dcc_info)
> 
> When SM_I(sbi) is NULL, it is used at some places, such as:
> LINE 88: reserved_segments(sbi)
>                    return SM_I(sbi)->reserved_segments;
> LINE 89: overprovision_segments(sbi)
>                    return SM_I(sbi)->ovp_segments;
> LINE 112: MAIN_SEGS(sbi)
>                      (SM_I(sbi)->main_segments)
> 
> Thus, possible null-pointer dereferences may occur.
> 
> These bugs are found by a static analysis tool STCheck written by us.
> 
> I do not know how to correctly fix these bugs, so I only report them.
> 
> 
> Best wishes,
> Jia-Ju Bai
> .
>