linux-ext4 - Re: [PATCH v2] ext4: avoid eh_entries overflow before insert extent

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Date:	Fri, 24 Jun 2011 14:49:34 +0800
From:	Yongqiang Yang <xiaoqiangnk@...il.com>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Robin Dong <hao.bigrat@...il.com>, linux-ext4@...r.kernel.org,
	Robin Dong <sanbai@...bao.com>
Subject: Re: [PATCH v2] ext4: avoid eh_entries overflow before insert extent_idx

On Thu, Jun 23, 2011 at 10:57 PM, Eric Sandeen <sandeen@...hat.com> wrote:
> On 6/23/11 3:47 AM, Robin Dong wrote:
>> If eh_entries is equal to (or greater than) eh_max, the operation of
>> inserting new extent_idx will make number of entries overflow.
>> So check eh_entries before inserting the new extent_idx.
>
> Do you have any testcase you can share which shows this bug?
I am not sure if Robin has any test case.

According to code, I think there is no bug case.  Because this
function is called by ext4_ext_split() and ext4_ext_split() is called
only if the index block has free space.

I think the right logic should be as this patch shows, that is, we
should lookup the capacity before insertion.

Yongqiang.
>
> Thanks,
> -Eric
>
>> Signed-off-by: Robin Dong <sanbai@...bao.com>
>> ---
>>  fs/ext4/extents.c |   18 ++++++++++--------
>>  1 files changed, 10 insertions(+), 8 deletions(-)
>>
>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>> index eb63c7b..792e77e 100644
>> --- a/fs/ext4/extents.c
>> +++ b/fs/ext4/extents.c
>> @@ -776,6 +776,16 @@ static int ext4_ext_insert_index(handle_t *handle, struct inode *inode,
>>                                logical, le32_to_cpu(curp->p_idx->ei_block));
>>               return -EIO;
>>       }
>> +
>> +     if (unlikely(le16_to_cpu(curp->p_hdr->eh_entries)
>> +                          >= le16_to_cpu(curp->p_hdr->eh_max))) {
>> +             EXT4_ERROR_INODE(inode,
>> +                              "eh_entries %d >= eh_max %d!",
>> +                              le16_to_cpu(curp->p_hdr->eh_entries),
>> +                              le16_to_cpu(curp->p_hdr->eh_max));
>> +             return -EIO;
>> +     }
>> +
>>       len = EXT_MAX_INDEX(curp->p_hdr) - curp->p_idx;
>>       if (logical > le32_to_cpu(curp->p_idx->ei_block)) {
>>               /* insert after */
>> @@ -805,14 +815,6 @@ static int ext4_ext_insert_index(handle_t *handle, struct inode *inode,
>>       ext4_idx_store_pblock(ix, ptr);
>>       le16_add_cpu(&curp->p_hdr->eh_entries, 1);
>>
>> -     if (unlikely(le16_to_cpu(curp->p_hdr->eh_entries)
>> -                          > le16_to_cpu(curp->p_hdr->eh_max))) {
>> -             EXT4_ERROR_INODE(inode,
>> -                              "eh_entries %d > eh_max %d!",
>> -                              le16_to_cpu(curp->p_hdr->eh_entries),
>> -                              le16_to_cpu(curp->p_hdr->eh_max));
>> -             return -EIO;
>> -     }
>>       if (unlikely(ix > EXT_LAST_INDEX(curp->p_hdr))) {
>>               EXT4_ERROR_INODE(inode, "ix > EXT_LAST_INDEX!");
>>               return -EIO;
>
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-- 
Best Wishes
Yongqiang Yang
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