linux-kernel - Re: [PATCH 4.14 58/62] mtd: rawnand: atmel: fix OF child-node lookup

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Date:   Mon, 26 Nov 2018 07:48:24 -0800
From:   Johan Hovold <johan@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Boris Brezillon <boris.brezillon@...tlin.com>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux- stable <stable@...r.kernel.org>,
        nicolas.ferre@...rochip.com, rainyfeeling@...look.com,
        johan@...nel.org
Subject: Re: [PATCH 4.14 58/62] mtd: rawnand: atmel: fix OF child-node lookup

On Mon, Nov 26, 2018 at 04:14:18PM +0100, Greg Kroah-Hartman wrote:
> On Mon, Nov 26, 2018 at 04:08:40PM +0100, Boris Brezillon wrote:
> > On Mon, 26 Nov 2018 19:46:15 +0530
> > Naresh Kamboju <naresh.kamboju@...aro.org> wrote:
> > 
> > > Do you see build failure arm x15 beagleboard on 4.14 due to this patch ?
> > > 
> > > On Mon, 26 Nov 2018 at 16:31, Greg Kroah-Hartman
> > > <gregkh@...uxfoundation.org> wrote:
> > > >
> > > > 4.14-stable review patch.  If anyone has any objections, please let me know.
> > > >
> > > > ------------------
> > > >
> > > > From: Johan Hovold <johan@...nel.org>
> > > >
> > > > commit 5d1e9c2212ea6b4dd735e4fc3dd6279a365d5d10 upstream.
> > > >
> > > > Use the new of_get_compatible_child() helper to lookup the nfc child
> > > > node instead of using of_find_compatible_node(), which searches the
> > > > entire tree from a given start node and thus can return an unrelated
> > > > (i.e. non-child) node.
> > > >
> > > > This also addresses a potential use-after-free (e.g. after probe
> > > > deferral) as the tree-wide helper drops a reference to its first
> > > > argument (i.e. the node of the device being probed).
> > > >
> > > > While at it, also fix a related nfc-node reference leak.
> > > >
> > > > Fixes: f88fc122cc34 ("mtd: nand: Cleanup/rework the atmel_nand driver")
> > > > Cc: stable <stable@...r.kernel.org>     # 4.11
> > > > Cc: Nicolas Ferre <nicolas.ferre@...rochip.com>
> > > > Cc: Josh Wu <rainyfeeling@...look.com>
> > > > Cc: Boris Brezillon <boris.brezillon@...tlin.com>
> > > > Signed-off-by: Johan Hovold <johan@...nel.org>
> > > > Signed-off-by: Boris Brezillon <boris.brezillon@...tlin.com>
> > > > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > >
> > > > ---
> > > >  drivers/mtd/nand/atmel/nand-controller.c |   11 +++++++----
> > > >  1 file changed, 7 insertions(+), 4 deletions(-)
> > > >
> > > > --- a/drivers/mtd/nand/atmel/nand-controller.c
> > > > +++ b/drivers/mtd/nand/atmel/nand-controller.c
> > > > @@ -2077,8 +2077,7 @@ atmel_hsmc_nand_controller_legacy_init(s
> > > >         int ret;
> > > >
> > > >         nand_np = dev->of_node;
> > > > -       nfc_np = of_find_compatible_node(dev->of_node, NULL,
> > > > -                                        "atmel,sama5d3-nfc");
> > > > +       nfc_np = of_get_compatible_child(dev->of_node, "atmel,sama5d3-nfc");
> > > >         if (!nfc_np) {
> > > >                 dev_err(dev, "Could not find device node for sama5d3-nfc\n");
> > > >                 return -ENODEV;
> > > > @@ -2492,15 +2491,19 @@ static int atmel_nand_controller_probe(s
> > > >         }
> > > >
> > > >         if (caps->legacy_of_bindings) {
> > > > +               struct device_node *nfc_node;
> > > >                 u32 ale_offs = 21;
> > > >
> > > >                 /*
> > > >                  * If we are parsing legacy DT props and the DT contains a
> > > >                  * valid NFC node, forward the request to the sama5 logic.
> > > >                  */
> > > > -               if (of_find_compatible_node(pdev->dev.of_node, NULL,
> > > > -                                           "atmel,sama5d3-nfc"))
> > > > +               nfc_node = of_get_compatible_child(pdev->dev.of_node,
> > > > +                                                  "atmel,sama5d3-nfc");
> > > > +               if (nfc_node) {
> > > >                         caps = &atmel_sama5_nand_caps;
> > > > +                       of_node_put(nfc_node);
> > > > +               }
> > > >
> > > >                 /*
> > > >                  * Even if the compatible says we are dealing with an
> > > >
> > > >  
> > > 
> > > /drivers/mtd/nand/atmel/nand-controller.c: In function
> > > 'atmel_hsmc_nand_controller_legacy_init':
> > > /drivers/mtd/nand/atmel/nand-controller.c:2080:11: error: implicit
> > > declaration of function 'of_get_compatible_child'; did you mean
> > > 'of_get_next_available_child'? [-Werror=implicit-function-declaration]
> > >    nfc_np = of_get_compatible_child(dev->of_node, "atmel,sama5d3-nfc");
> > 
> > Looks like of_get_compatible_child() has been introduced in 4.18, hence
> > this error.
> > 
> > Greg, can you drop this patch from 4.14.y?
> 
> Yes, my fault, I fixed a number of these in the past, missed this one :(
> 
> Now dropped.

The intention here was that the helper should be backported along with
the fixes. I mentioned this in the cover letter to the series
introducing the helper and the fixes. As they were submitted together I
could not use the usual

	Cc: stable <stable@...r.kernel.org>	# 4.xx: 36156f9241cb

notation for this. I realise I should still have mentioned this in each
individual commit messages as well, sorry about that.

The dependency for all of these fixes is:

	36156f9241cb ("of: add helper to lookup compatible child node")

and the original thread can be found here:

	https://lkml.kernel.org/r/20180827082153.22537-1-johan@kernel.org
	
Johan