linux-kernel - Re: [PATCH] ubifs: Free memory for tmpfile name

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Date:   Thu, 30 Mar 2023 16:21:22 +0800
From:   Zhihao Cheng <chengzhihao1@...wei.com>
To:     Mårten Lindahl <martenli@...s.com>,
        Mårten Lindahl <marten.lindahl@...s.com>,
        Richard Weinberger <richard@....at>
CC:     <linux-mtd@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <kernel@...s.com>
Subject: Re: [PATCH] ubifs: Free memory for tmpfile name

Hi Mårten,
> Hi Zhihao!
> 
> On 3/30/23 04:25, Zhihao Cheng wrote:
>> Hi Mårten,
>>> When opening a ubifs tmpfile on an encrypted directory, function
>>> fscrypt_setup_filename allocates memory for the name that is to be
>>> stored in the directory entry, but after the name has been copied to the
>>> directory entry inode, the memory is not freed.
>>>
>>> When running kmemleak on it we see that it is registered as a leak. The
>>> report below is triggered by a simple program 'tmpfile' just opening a
>>> tmpfile:
>>>
>>>    unreferenced object 0xffff88810178f380 (size 32):
>>>      comm "tmpfile", pid 509, jiffies 4294934744 (age 1524.742s)
>>>      backtrace:
>>>        __kmem_cache_alloc_node
>>>        __kmalloc
>>>        fscrypt_setup_filename
>>>        ubifs_tmpfile
>>>        vfs_tmpfile
>>>        path_openat
>>>
>>> Free this memory after it has been copied to the inode.
>>>
>>> Signed-off-by: Mårten Lindahl <marten.lindahl@...s.com>
>>> ---
>>>   fs/ubifs/dir.c | 1 +
>>>   1 file changed, 1 insertion(+)
>>>
>>> diff --git a/fs/ubifs/dir.c b/fs/ubifs/dir.c
>>> index 0f29cf201136..089ca6910124 100644
>>> --- a/fs/ubifs/dir.c
>>> +++ b/fs/ubifs/dir.c
>>> @@ -491,6 +491,7 @@ static int ubifs_tmpfile(struct user_namespace 
>>> *mnt_userns, struct inode *dir,
>>>           goto out_cancel;
>>>       unlock_2_inodes(dir, inode);
>>>   +    fscrypt_free_filename(&nm);
>>>       ubifs_release_budget(c, &req);
>>>         return finish_open_simple(file, 0);
>>
>> Looks good, just one small nit. I'd prefer to add 
>> fscrypt_free_filename() after ubifs_release_budget() just like 
>> ubifs_create/link does, so that ubifs can get unused budget earlier.
> OK, I will move it after ubifs_release_budget.
>>
>> After looking through the code, I found another place create_whiteout 
>> has the same problem(Imported in 278d9a243635f26c05("ubifs: Rename 
>> whiteout atomically") by me). Would you mind fixing this point just by 
>> removing unused 'nm' in create_whiteout()?
> 
> I see what you mean. As I understand it calling fscrypt_setup_filename 
> is not needed in create_whiteout. I would prefer removing those lines in 
> a separate patch since that leak is related to do_rename(). If it's OK 
> with you I can make a patch for that. Would that be OK?
> 

Yes. You may send another patch to fix it. Thanks.