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

["Sascha Hauer" <s.hauer@pengutronix.de>]

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.

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

Sascha

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