[PATCH] f2fs: fix ctx->pos in f2fs_read_inline_dir()

[PATCH] f2fs: fix ctx->pos in f2fs_read_inline_dir()

[Yangtao Li]

I recently found a case where de->name_len is 0 in f2fs_fill_dentries() easily reproduced,
and finally set the fsck flag.

Thread A					Thread B

f2fs_readdir
	f2fs_read_inline_dir
		ctx->pos = d.max
						f2fs_add_dentry
							f2fs_add_inline_entry
								do_convert_inline_dir
							f2fs_add_regular_entry
f2fs_readdir
	f2fs_fill_dentries
		set_sbi_flag(sbi, SBI_NEED_FSCK)

Process A opens the folder, and has been reading without closing it. During this period,
Process B created a file under the folder (occupying multiple f2fs_dir_entry, exceeding
the d.max of the inline dir). After creation, process A uses the d.max of inline dir to
read it again, and it will read that de->name_len is 0.

And returning early in f2fs_read_inline_dir will cause the process to be unable to see
the changes before reopening the file.

So don't return early and remove the modification of ctx->pos in f2fs_read_inline_dir().

Signed-off-by: Yangtao Li <frank.li@vivo.com>
---
 fs/f2fs/inline.c | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/fs/f2fs/inline.c b/fs/f2fs/inline.c
index 56a20d5c15da..fc6551139a3d 100644
--- a/fs/f2fs/inline.c
+++ b/fs/f2fs/inline.c
@@ -729,9 +729,6 @@ int f2fs_read_inline_dir(struct file *file, struct dir_context *ctx,
 
 	make_dentry_ptr_inline(inode, &d, inline_dentry);
 
-	if (ctx->pos == d.max)
-		return 0;
-
 	ipage = f2fs_get_node_page(F2FS_I_SB(inode), inode->i_ino);
 	if (IS_ERR(ipage))
 		return PTR_ERR(ipage);
@@ -747,8 +744,6 @@ int f2fs_read_inline_dir(struct file *file, struct dir_context *ctx,
 	make_dentry_ptr_inline(inode, &d, inline_dentry);
 
 	err = f2fs_fill_dentries(ctx, &d, 0, fstr);
-	if (!err)
-		ctx->pos = d.max;
 
 	f2fs_put_page(ipage, 0);
 	return err < 0 ? err : 0;
-- 
2.32.0

Re: [f2fs-dev] [PATCH] f2fs: fix ctx->pos in f2fs_read_inline_dir()

[Chao Yu]

On 2021/7/17 11:49, Yangtao Li wrote:
> I recently found a case where de->name_len is 0 in f2fs_fill_dentries() easily reproduced,
> and finally set the fsck flag.
> 
> Thread A					Thread B
> 
> f2fs_readdir
> 	f2fs_read_inline_dir
> 		ctx->pos = d.max
> 						f2fs_add_dentry
> 							f2fs_add_inline_entry
> 								do_convert_inline_dir
> 							f2fs_add_regular_entry
> f2fs_readdir
> 	f2fs_fill_dentries
> 		set_sbi_flag(sbi, SBI_NEED_FSCK)
> 
> Process A opens the folder, and has been reading without closing it. During this period,
> Process B created a file under the folder (occupying multiple f2fs_dir_entry, exceeding
> the d.max of the inline dir). After creation, process A uses the d.max of inline dir to
> read it again, and it will read that de->name_len is 0.

Nice catch!

> 
> And returning early in f2fs_read_inline_dir will cause the process to be unable to see
> the changes before reopening the file.
> 
> So don't return early and remove the modification of ctx->pos in f2fs_read_inline_dir().
> 
> Signed-off-by: Yangtao Li <frank.li@vivo.com>
> ---
>   fs/f2fs/inline.c | 5 -----
>   1 file changed, 5 deletions(-)
> 
> diff --git a/fs/f2fs/inline.c b/fs/f2fs/inline.c
> index 56a20d5c15da..fc6551139a3d 100644
> --- a/fs/f2fs/inline.c
> +++ b/fs/f2fs/inline.c
> @@ -729,9 +729,6 @@ int f2fs_read_inline_dir(struct file *file, struct dir_context *ctx,
>   
>   	make_dentry_ptr_inline(inode, &d, inline_dentry);
>   
> -	if (ctx->pos == d.max)
> -		return 0;
> -
>   	ipage = f2fs_get_node_page(F2FS_I_SB(inode), inode->i_ino);
>   	if (IS_ERR(ipage))
>   		return PTR_ERR(ipage);
> @@ -747,8 +744,6 @@ int f2fs_read_inline_dir(struct file *file, struct dir_context *ctx,
>   	make_dentry_ptr_inline(inode, &d, inline_dentry);
>   
>   	err = f2fs_fill_dentries(ctx, &d, 0, fstr);

After this function, ctx->pos will point to start position of first free slot after
last dir_entry, we can't guarantee that the free slot won't be used in above race
condition, right?

Moreover, w/o inline conversion, the race condition still can happen as below, right?

dir_entry1: A
dir_entry2: B
dir_entry3: C
free slot: _

Before:
AAAABBBB___
         ^
Thread B delete dir_entry2, and create dir_entry3.

After:
AAAACCCCC__
         ^
Thanks,

> -	if (!err)
> -		ctx->pos = d.max;
>   
>   	f2fs_put_page(ipage, 0);
>   	return err < 0 ? err : 0;
> 

Re:Re: [f2fs-dev] [PATCH] f2fs: fix ctx->pos in f2fs_read_inline_dir()

[李扬韬]

HI Chao,

From: Chao Yu <chao@kernel.org>
Date: 2021-07-17 16:56:01
To:  Yangtao Li <frank.li@vivo.com>,jaegeuk@kernel.org
Cc:  linux-kernel@vger.kernel.org,linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: fix ctx->pos in f2fs_read_inline_dir()>On 2021/7/17 11:49, Yangtao Li wrote:
>> I recently found a case where de->name_len is 0 in f2fs_fill_dentries() easily reproduced,
>> and finally set the fsck flag.
>> 
>> Thread A					Thread B
>> 
>> f2fs_readdir
>> 	f2fs_read_inline_dir
>> 		ctx->pos = d.max
>> 						f2fs_add_dentry
>> 							f2fs_add_inline_entry
>> 								do_convert_inline_dir
>> 							f2fs_add_regular_entry
>> f2fs_readdir
>> 	f2fs_fill_dentries
>> 		set_sbi_flag(sbi, SBI_NEED_FSCK)
>> 
>> Process A opens the folder, and has been reading without closing it. During this period,
>> Process B created a file under the folder (occupying multiple f2fs_dir_entry, exceeding
>> the d.max of the inline dir). After creation, process A uses the d.max of inline dir to
>> read it again, and it will read that de->name_len is 0.
>
>Nice catch!
>
>> 
>> And returning early in f2fs_read_inline_dir will cause the process to be unable to see
>> the changes before reopening the file.
>> 
>> So don't return early and remove the modification of ctx->pos in f2fs_read_inline_dir().
>> 
>> Signed-off-by: Yangtao Li <frank.li@vivo.com>
>> ---
>>   fs/f2fs/inline.c | 5 -----
>>   1 file changed, 5 deletions(-)
>> 
>> diff --git a/fs/f2fs/inline.c b/fs/f2fs/inline.c
>> index 56a20d5c15da..fc6551139a3d 100644
>> --- a/fs/f2fs/inline.c
>> +++ b/fs/f2fs/inline.c
>> @@ -729,9 +729,6 @@ int f2fs_read_inline_dir(struct file *file, struct dir_context *ctx,
>>   
>>   	make_dentry_ptr_inline(inode, &d, inline_dentry);
>>   
>> -	if (ctx->pos == d.max)
>> -		return 0;
>> -
>>   	ipage = f2fs_get_node_page(F2FS_I_SB(inode), inode->i_ino);
>>   	if (IS_ERR(ipage))
>>   		return PTR_ERR(ipage);
>> @@ -747,8 +744,6 @@ int f2fs_read_inline_dir(struct file *file, struct dir_context *ctx,
>>   	make_dentry_ptr_inline(inode, &d, inline_dentry);
>>   
>>   	err = f2fs_fill_dentries(ctx, &d, 0, fstr);
>
>After this function, ctx->pos will point to start position of first free slot after
>last dir_entry, we can't guarantee that the free slot won't be used in above race
>condition, right?
>
>Moreover, w/o inline conversion, the race condition still can happen as below, right?
>
>dir_entry1: A
>dir_entry2: B
>dir_entry3: C
>free slot: _
>
>Before:
>AAAABBBB___
>         ^
>Thread B delete dir_entry2, and create dir_entry3.
>
>After:
>AAAACCCCC__
>         ^

Taking into account the above situations, I think this case where de->name_len is 0 in f2fs_fill_dentries()
should be normal and there is no way to avoid it. Maybe we shouldn't set fsck flag at this time?
Because the file system is not damaged.

MBR / Yangtao

Re: [f2fs-dev] [PATCH] f2fs: fix ctx->pos in f2fs_read_inline_dir()

[Chao Yu]

On 2021/7/17 21:25, 李扬韬 wrote:
> HI Chao,
> 
> From: Chao Yu <chao@kernel.org>
> Date: 2021-07-17 16:56:01
> To:  Yangtao Li <frank.li@vivo.com>,jaegeuk@kernel.org
> Cc:  linux-kernel@vger.kernel.org,linux-f2fs-devel@lists.sourceforge.net
> Subject: Re: [f2fs-dev] [PATCH] f2fs: fix ctx->pos in f2fs_read_inline_dir()>On 2021/7/17 11:49, Yangtao Li wrote:
>>> I recently found a case where de->name_len is 0 in f2fs_fill_dentries() easily reproduced,
>>> and finally set the fsck flag.
>>>
>>> Thread A					Thread B
>>>
>>> f2fs_readdir
>>> 	f2fs_read_inline_dir
>>> 		ctx->pos = d.max
>>> 						f2fs_add_dentry
>>> 							f2fs_add_inline_entry
>>> 								do_convert_inline_dir
>>> 							f2fs_add_regular_entry
>>> f2fs_readdir
>>> 	f2fs_fill_dentries
>>> 		set_sbi_flag(sbi, SBI_NEED_FSCK)
>>>
>>> Process A opens the folder, and has been reading without closing it. During this period,
>>> Process B created a file under the folder (occupying multiple f2fs_dir_entry, exceeding
>>> the d.max of the inline dir). After creation, process A uses the d.max of inline dir to
>>> read it again, and it will read that de->name_len is 0.
>>
>> Nice catch!
>>
>>>
>>> And returning early in f2fs_read_inline_dir will cause the process to be unable to see
>>> the changes before reopening the file.
>>>
>>> So don't return early and remove the modification of ctx->pos in f2fs_read_inline_dir().
>>>
>>> Signed-off-by: Yangtao Li <frank.li@vivo.com>
>>> ---
>>>    fs/f2fs/inline.c | 5 -----
>>>    1 file changed, 5 deletions(-)
>>>
>>> diff --git a/fs/f2fs/inline.c b/fs/f2fs/inline.c
>>> index 56a20d5c15da..fc6551139a3d 100644
>>> --- a/fs/f2fs/inline.c
>>> +++ b/fs/f2fs/inline.c
>>> @@ -729,9 +729,6 @@ int f2fs_read_inline_dir(struct file *file, struct dir_context *ctx,
>>>    
>>>    	make_dentry_ptr_inline(inode, &d, inline_dentry);
>>>    
>>> -	if (ctx->pos == d.max)
>>> -		return 0;
>>> -
>>>    	ipage = f2fs_get_node_page(F2FS_I_SB(inode), inode->i_ino);
>>>    	if (IS_ERR(ipage))
>>>    		return PTR_ERR(ipage);
>>> @@ -747,8 +744,6 @@ int f2fs_read_inline_dir(struct file *file, struct dir_context *ctx,
>>>    	make_dentry_ptr_inline(inode, &d, inline_dentry);
>>>    
>>>    	err = f2fs_fill_dentries(ctx, &d, 0, fstr);
>>
>> After this function, ctx->pos will point to start position of first free slot after
>> last dir_entry, we can't guarantee that the free slot won't be used in above race
>> condition, right?
>>
>> Moreover, w/o inline conversion, the race condition still can happen as below, right?
>>
>> dir_entry1: A
>> dir_entry2: B
>> dir_entry3: C
>> free slot: _
>>
>> Before:
>> AAAABBBB___
>>          ^
>> Thread B delete dir_entry2, and create dir_entry3.
>>
>> After:
>> AAAACCCCC__
>>          ^
> 
> Taking into account the above situations, I think this case where de->name_len is 0 in f2fs_fill_dentries()
> should be normal and there is no way to avoid it. Maybe we shouldn't set fsck flag at this time?
> Because the file system is not damaged.

Yangtao,

IMO, it should bypass tagging FSCK flag only if:
a) bit_pos (:= ctx->pos % d->max) is non-zero & b) before bit_pos moves to first
valid dir_entry.

Thanks,

> 
> MBR / Yangtao
> 
>