linux-kernel - Re: [PATCH v2 3/5] f2fs: fix to avoid NULL pointer dereference

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Date:   Thu, 26 Mar 2020 17:30:27 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>, <chao@...nel.org>
Subject: Re: [PATCH v2 3/5] f2fs: fix to avoid NULL pointer dereference

Hi Jaegeuk,

I've made that diff as a patch and changed title and commit message a
bit, let's merge the new one.

Thanks,

On 2020/3/25 23:50, Jaegeuk Kim wrote:
> Hi Chao,
> 
> I don't want to rebase old commit at this moment, so applied on top of the tree.
> 
> Thanks,
> 
> On 03/25, Chao Yu wrote:
>> Unable to handle kernel NULL pointer dereference at virtual address 00000000
>> PC is at f2fs_free_dic+0x60/0x2c8
>> LR is at f2fs_decompress_pages+0x3c4/0x3e8
>> f2fs_free_dic+0x60/0x2c8
>> f2fs_decompress_pages+0x3c4/0x3e8
>> __read_end_io+0x78/0x19c
>> f2fs_post_read_work+0x6c/0x94
>> process_one_work+0x210/0x48c
>> worker_thread+0x2e8/0x44c
>> kthread+0x110/0x120
>> ret_from_fork+0x10/0x18
>>
>> In f2fs_free_dic(), we can not use f2fs_put_page(,1) to release dic->tpages[i],
>> as the page's mapping is NULL.
>>
>> Signed-off-by: Chao Yu <yuchao0@...wei.com>
>> ---
>> v2:
>> - fix to skip release tpages[i] if it is NULL in error path.
>>  fs/f2fs/compress.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
>> index ef7dd04312fe..6e10800729b6 100644
>> --- a/fs/f2fs/compress.c
>> +++ b/fs/f2fs/compress.c
>> @@ -1137,7 +1137,10 @@ void f2fs_free_dic(struct decompress_io_ctx *dic)
>>  		for (i = 0; i < dic->cluster_size; i++) {
>>  			if (dic->rpages[i])
>>  				continue;
>> -			f2fs_put_page(dic->tpages[i], 1);
>> +			if (!dic->tpages[i])
>> +				continue;
>> +			unlock_page(dic->tpages[i]);
>> +			put_page(dic->tpages[i]);
>>  		}
>>  		kfree(dic->tpages);
>>  	}
>> -- 
>> 2.18.0.rc1
> .
>