linux-kernel - Re: [f2fs-dev] [PATCH 3/4] f2fs: fix NULL pointer dereference in f2fs_verity

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Message-ID: <915e56c1-3e87-ef0a-8bdf-26a3774b0a18@kernel.org>
Date:   Sat, 21 Mar 2020 20:16:52 +0800
From:   Chao Yu <chao@...nel.org>
To:     Eric Biggers <ebiggers@...nel.org>, Chao Yu <yuchao0@...wei.com>
Cc:     jaegeuk@...nel.org, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 3/4] f2fs: fix NULL pointer dereference in
 f2fs_verity_work()

On 2020-3-21 3:11, Eric Biggers wrote:
> On Thu, Mar 19, 2020 at 07:57:59PM +0800, Chao Yu wrote:
>> If both compression and fsverity feature is on, generic/572 will
>> report below NULL pointer dereference bug.
>>
>>  BUG: kernel NULL pointer dereference, address: 0000000000000018
>>  RIP: 0010:f2fs_verity_work+0x60/0x90 [f2fs]
>>  #PF: supervisor read access in kernel mode
>>  Workqueue: fsverity_read_queue f2fs_verity_work [f2fs]
>>  RIP: 0010:f2fs_verity_work+0x60/0x90 [f2fs]
>>  Call Trace:
>>   process_one_work+0x16c/0x3f0
>>   worker_thread+0x4c/0x440
>>   ? rescuer_thread+0x350/0x350
>>   kthread+0xf8/0x130
>>   ? kthread_unpark+0x70/0x70
>>   ret_from_fork+0x35/0x40
>>
>> There are two issue in f2fs_verity_work():
>> - it needs to traverse and verify all pages in bio.
>> - if pages in bio belong to non-compressed cluster, accessing
>> decompress IO context stored in page private will cause NULL
>> pointer dereference.
>>
>> Fix them.
>>
>> Signed-off-by: Chao Yu <yuchao0@...wei.com>
>> ---
>>  fs/f2fs/data.c | 35 ++++++++++++++++++++++++++++++-----
>>  1 file changed, 30 insertions(+), 5 deletions(-)
>>
>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>> index 5c5db09324b7..66e49fc1056e 100644
>> --- a/fs/f2fs/data.c
>> +++ b/fs/f2fs/data.c
>> @@ -187,12 +187,37 @@ static void f2fs_verify_pages(struct page **rpages, unsigned int cluster_size)
>>
>>  static void f2fs_verify_bio(struct bio *bio)
>>  {
>> -	struct page *page = bio_first_page_all(bio);
>> -	struct decompress_io_ctx *dic =
>> -			(struct decompress_io_ctx *)page_private(page);
>> +	struct bio_vec *bv;
>> +	struct bvec_iter_all iter_all;
>> +	struct decompress_io_ctx *dic, *pdic = NULL;
>> +
>> +	bio_for_each_segment_all(bv, bio, iter_all) {
>> +		struct page *page = bv->bv_page;
>> +
>> +		dic = (struct decompress_io_ctx *)page_private(page);
>> +
>> +		if (dic) {
>> +			if (dic != pdic) {
>> +				f2fs_verify_pages(dic->rpages,
>> +							dic->cluster_size);
>> +				f2fs_free_dic(dic);
>> +				pdic = dic;
>> +			}
>> +			continue;
>> +		}
>> +		pdic = dic;
>>
>> -	f2fs_verify_pages(dic->rpages, dic->cluster_size);
>> -	f2fs_free_dic(dic);
>> +		if (bio->bi_status || PageError(page)) {
>> +			ClearPageUptodate(page);
>> +			ClearPageError(page);
>> +		} else {
>> +			if (fsverity_verify_page(page))
>> +				SetPageUptodate(page);
>> +			else
>> +				SetPageError(page);
>> +		}
>> +		unlock_page(page);
>> +	}
>
> I'm a bit confused why you added SetPageError() before unlocking the page.
> The other error paths actually clear the Error flag, not set it.  I thought
> there's a reason for that?

These codes were copy&paste from f2fs_decompress_end_io(), I guess I missed to 
check that logic, so anyway, we need another patch to fix that first.

Thanks for pointing out this.

Thanks,

>
> - Eric
>
>
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