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

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Date:   Thu, 30 Mar 2023 09:54:46 +0200
From:   Mårten Lindahl <martenli@...s.com>
To:     Zhihao Cheng <chengzhihao1@...wei.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 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?

Kind regards

Mårten

>>
>> ---
>> base-commit: c9c3395d5e3dcc6daee66c6908354d47bf98cb0c
>> change-id: 20230329-memleak-fix-87a01daf469e
>>
>> Best regards,
>>
>