Re: [PATCH] of: overlay: fix memory leak in add_changeset_node()

[Zeng Heng]

On 2022/11/21 10:00, Frank Rowand wrote:
> On 11/18/22 04:53, Zeng Heng wrote:
> > In of_changeset_action(), we have called of_node_get() to increase
> > refcount of a node.
> >
> > Therefore, when tchild (duplicated by __of_node_dup()) is done,
> > of_node_put() needs to call and release the device_node.
> >
> > Otherwise, there are some memory leak reported about the node:
> >
> > unreferenced object 0xffff88810cd1e800 (size 256):
> >    backtrace:
> >      kmalloc_trace
> >      __of_node_dup
> >      add_changeset_node (inlined)
> >      build_changeset_next_level
> >
> > unreferenced object 0xffff888113721240 (size 16):
> >    backtrace:
> >      __kmalloc_node_track_caller
> >      kstrdup
> >      __of_node_dup
> >      add_changeset_node (inlined)
> >      build_changeset_next_level
> >
> > unreferenced object 0xffff88810a38d400 (size 128):
> >    backtrace:
> >      kmalloc_trace
> >      __of_prop_dup
> >      add_changeset_property
> >      build_changeset_next_level
> >
> > Fixes: 7518b5890d8a ("of/overlay: Introduce DT overlay support")
> > Signed-off-by: Zeng Heng<zengheng4@xxxxxxxxxx>
> > ---
> >   drivers/of/overlay.c | 4 +++-
> >   1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> > index bd8ff4df723d..a5189a0ec0a3 100644
> > --- a/drivers/of/overlay.c
> > +++ b/drivers/of/overlay.c
> > @@ -436,8 +436,10 @@ static int add_changeset_node(struct overlay_changeset *ovcs,
> >   		of_node_set_flag(tchild, OF_OVERLAY);
> >   
> >   		ret = of_changeset_attach_node(&ovcs->cset, tchild);
> > -		if (ret)
> > +		if (ret) {
> > +			of_node_put(tchild);
> >   			return ret;
> > +		}
> By visual inspection of the code (Linux 6.1-rc1), this does not appear to be
> correct.  For the only case where of_changeset_action(),
> called by of_changeset_attach_node(), returns an error, of_node_get() has not
> yet occurred on tchild.

The correct explanation should be like:

When of_changeset_attach_node() returns fail and tchild is over of life 
cycle which is duplicated by

__of_node_dup(), it needs to call of_node_put() to release tchild in 
error handle route.


The patch is fine, but feel sorry to apologize for the incorrect comment 
of the patch.

I would update the comment in the patch v2.


With Best Regards,

Zeng Heng

> >   
> >   		target_child.np = tchild;
> >   		target_child.in_livetree = false;
> For which version of Linux were the memory leaks detected?  Were any additional
> patches applied?
>
> -Frank