Re: [PATCH 1/2] fs: ubifs: zero initialize allocated inode

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

Hi,

On 5/19/26 3:14 PM, Sascha Hauer wrote:
> On 2026-05-19 15:03, Ahmad Fatoum wrote:
>> Hi,
>>
>> On 5/19/26 2:44 PM, Sascha Hauer wrote:
>>> UBIFS uses kmem_cache_alloc() to allocate an ubifs_inode. The memory
>>> returned from kmem_cache_alloc() is not zeroed. ubifs_alloc_inode()
>>> zeroes all fields in the ubifs_inode except the embedded struct inode.
>>> In Linux this is done in the kmem_cache constructor function which calls
>>> inode_init_once(). In barebox we have the constructor function as well,
>>> but we don't have an equivalent of inode_init_once(), so the constructor
>>> is empty.  zero the inode in the constructor instead so that barebox
>>> gets a zeroed inode.
>>>
>>> Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
>>> ---
>>>  fs/ubifs/super.c | 1 +
>>>  1 file changed, 1 insertion(+)
>>>
>>> diff --git a/fs/ubifs/super.c b/fs/ubifs/super.c
>>> index 45037b42ea..4022270d4c 100644
>>> --- a/fs/ubifs/super.c
>>> +++ b/fs/ubifs/super.c
>>> @@ -1128,6 +1128,7 @@ static void kill_ubifs_super(struct super_block *s)
>>>   */
>>>  static void inode_slab_ctor(void *obj)
>>>  {
>>> +	memset(obj, 0, sizeof(struct inode));
>>
>> This works because inode is the first member of struct ubifs_inode, but
>> I would prefer to avoid depending on that as it might change with a
>> future update.
>>
>> Can't we just zero all of struct ubifs_inode here to be on the safe side?
> 
> That was my first approach as well, but I was afraid this could be lost
> on an UBIFS update.
> 
> I could treat obj as a struct ubifs_inode and zero the inode member
> instead.

Yes, that would work too.

> 
> That would have prevented the bug I introduced with the JFFS2 patch as
> well.
> 
> Sascha
> 
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