linux-kernel - Re: [PATCH 1/3] fs: ocfs2: Fix possible null-pointer dereferences in ocfs2_xa_prepare

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Message-ID: <620ac436-ffbc-8429-b952-278cd2a8aaba@gmail.com>
Date:   Fri, 26 Jul 2019 17:50:06 +0800
From:   Jia-Ju Bai <baijiaju1990@...il.com>
To:     Joseph Qi <joseph.qi@...ux.alibaba.com>, mark@...heh.com,
        jlbec@...lplan.org
Cc:     ocfs2-devel@....oracle.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] fs: ocfs2: Fix possible null-pointer dereferences in
 ocfs2_xa_prepare_entry()



On 2019/7/26 17:37, Joseph Qi wrote:
>
> On 19/7/26 11:36, Jia-Ju Bai wrote:
>> In ocfs2_xa_prepare_entry(), there is an if statement on line 2136 to
>> check whether loc->xl_entry is NULL:
>>      if (loc->xl_entry)
>>
>> When loc->xl_entry is NULL, it is used on line 2158:
>>      ocfs2_xa_add_entry(loc, name_hash);
>>          loc->xl_entry->xe_name_hash = cpu_to_le32(name_hash);
>>          loc->xl_entry->xe_name_offset = cpu_to_le16(loc->xl_size);
>> and line 2164:
>> 	ocfs2_xa_add_namevalue(loc, xi);
>>          loc->xl_entry->xe_value_size = cpu_to_le64(xi->xi_value_len);
>>          loc->xl_entry->xe_name_len = xi->xi_name_len;
>>
>> Thus, possible null-pointer dereferences may occur.
>>
>> To fix these bugs, if loc-xl_entry is NULL, ocfs2_xa_prepare_entry()
>> abnormally returns with -EINVAL.
>>
>> These bugs are found by a static analysis tool STCheck written by us.
>>
>> Signed-off-by: Jia-Ju Bai <baijiaju1990@...il.com>
>> ---
>>   fs/ocfs2/xattr.c | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
>> index 385f3aaa2448..f690502daf3c 100644
>> --- a/fs/ocfs2/xattr.c
>> +++ b/fs/ocfs2/xattr.c
>> @@ -2154,8 +2154,10 @@ static int ocfs2_xa_prepare_entry(struct ocfs2_xa_loc *loc,
>>   			}
>>   		}
>>   		ocfs2_xa_wipe_namevalue(loc);
>> -	} else
>> -		ocfs2_xa_add_entry(loc, name_hash);
>> +	} else {
>> +		rc = -EINVAL;
>> +		goto out;
>> +	}
> Since entry not found, so there is nothing to do in
> ocfs2_xa_prepare_entry(). We may change it like:
>
> if (!loc->xl_entry) {
> 	rc = -EINVAL;
> 	goto out;
> }	
>
> if (ocfs2_xa_can_reuse_entry(loc, xi)) {
> 	......
> }
> .....
>

Okay, I will send a v2 patch.


Best wishes,
Jia-Ju Bai