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Message-ID: <Z1ITwpJcwPNc37X_@google.com>
Date: Thu, 5 Dec 2024 12:57:38 -0800
From: Dmitry Torokhov <dmitry.torokhov@...il.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
Sakari Ailus <sakari.ailus@...ux.intel.com>,
Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
Daniel Scally <djrscally@...il.com>, linux-acpi@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] device property: do not leak child nodes when using
NULL/error pointers
On Wed, Dec 04, 2024 at 03:16:34AM +0200, Andy Shevchenko wrote:
> On Tue, Dec 03, 2024 at 02:45:49PM -0800, Dmitry Torokhov wrote:
> > On Tue, Dec 03, 2024 at 03:27:31PM +0200, Andy Shevchenko wrote:
> > > On Mon, Dec 02, 2024 at 09:49:06PM -0800, Dmitry Torokhov wrote:
> > > > On Sat, Nov 30, 2024 at 11:44:04PM +0200, Andy Shevchenko wrote:
> > > > > On Fri, Nov 29, 2024 at 11:16:54PM -0800, Dmitry Torokhov wrote:
> > > > > > On Fri, Nov 29, 2024 at 04:50:15PM +0200, Andy Shevchenko wrote:
> > > > > > > On Thu, Nov 28, 2024 at 03:04:50PM -0800, Dmitry Torokhov wrote:
> > > > > > > > On Thu, Nov 28, 2024 at 03:13:16PM +0200, Andy Shevchenko wrote:
> > > > > > > > > On Wed, Nov 27, 2024 at 09:39:34PM -0800, Dmitry Torokhov wrote:
>
> ...
>
> > > > > > > > > > @@ struct fwnode_handle *device_get_next_child_node(const struct device *dev,
> > > > > > > > > > const struct fwnode_handle *fwnode = dev_fwnode(dev);
> > > > > > > > > > struct fwnode_handle *next;
> > > > > > > > >
> > > > > > > > > > - if (IS_ERR_OR_NULL(fwnode))
> > > > > > > > > > + if (IS_ERR_OR_NULL(fwnode)) {
> > > > > > > > > > + fwnode_handle_put(child);
> > > > > > > > > > return NULL;
> > > > > > > > > > + }
> > > > > > > > >
> > > > > > > > > > /* Try to find a child in primary fwnode */
> > > > > > > > > > next = fwnode_get_next_child_node(fwnode, child);
> > > > > > > > >
> > > > > > > > > So, why not just moving the original check (w/o dropping the reference) here?
> > > > > > > > > Wouldn't it have the same effect w/o explicit call to the fwnode_handle_put()?
> > > > > > > >
> > > > > > > > Because if you rely on check in fwnode_get_next_child_node() you would
> > > > > > > > not know if it returned NULL because there are no more children or
> > > > > > > > because the node is invalid. In the latter case you can't dereference
> > > > > > > > fwnode->secondary.
> > > > > > >
> > > > > > > Yes, so, how does it contradict my proposal?
> > > > > >
> > > > > > I guess I misunderstood your proposal then. Could you please explain it
> > > > > > in more detail?
> > > > >
> > > > >
> > > > > Current code (in steps):
> > > > > if (IS_ERR_OR_NULL()) check
> > > > > trying primary
> > > > > trying secondary if previous is NULL
> > > > >
> > > > >
> > > > > My proposal
> > > > >
> > > > > trying primary
> > > > > return if not NULL
> > > > > if (IS_ERR_OR_NULL()) check in its current form (no put op)
> > > > > trying secondary
> > > > >
> > > > > After your first patch IIUC this is possible as trying primary will put child uncoditionally.
> > > >
> > > > Ah, I see. No, I do not think this is a good idea: it will make the code
> > > > harder to understand for a casual reader: "Why do we check node validity
> > > > only after we used it for the first time?"
> > >
> > > Theare a re already a few API calls there that are hard to understand, I spent
> > > some time on them to get it through and still got it wrong as this series
> > > shows. So, I don't think we anyhow change this.
> >
> > The fact that some code is confusing does not mean that we should add
> > more confusing code. We will not fix everything at once, but we can make
> > things better bit by bit.
> >
> > Look, the check where it is now makes total sense, you added it there
> > yourself! It checks that we are dealing with a valid node and returns
> > early. The intent is very easy to understand and the only thing that is
> > missing is that "put" operation to satisfy the documented behavior.
> > Anything more just makes things more complex for no good reason.
>
> Right, that's why I think we need to go away from open coding the iteration
> over the list of nodes (primary, secondary, etc).
>
> > > > For the code not in a hot path there is a lot of value in simplicity.
> > >
> > > If you really want to go to this rabbit hole, think how we can get rid of
> > > repetitive checks of the secondary or more if any in the future nodes in the
> > > list.
> > >
> > > So the basic idea is to have this all hidden (to some extent) behind the macro
> > > or alike. In the code it would be something as
> > >
> > > for node in primary, secondary, ...
> > > call the API
> > > if (okay)
> > > return result
> > >
> > > return error
> > >
> > > This will indeed help.
> >
> > I think this will indeed help if we ever going to have more than primary
> > and secondary nodes. It is also tricky if you want to transition
> > seamlessly between different types of nodes (i.e. you have ACPI primary
> > with OF overlay secondary with swnode as tertiary etc). And you probably
> > want to add support for references between different typesof nodes
> > (i.e. swnode being able to reference OF device node for example).
> >
> > This kind of rework is however out of scope of what I have time to do at
> > the moment.
>
> I am not asking you to invest into big rework, the idea is to try to fold the
> iterations to a kind of loop. Is it feasible?
We could potentially do something like below.
BTW, do you know why fwnode_property_get_reference_args() returns
-ENOENT for NULL or error fwnode instead of -EINVAL as the rest of them?
And would you object to unifying this?
Thanks.
--
Dmitry
index 0ca3c0908b0c..3b4c394138e2 100644
--- a/drivers/base/property.c
+++ b/drivers/base/property.c
@@ -18,6 +18,28 @@
#include <linux/string.h>
#include <linux/types.h>
+#define FWNODE_ITERATE(n, result, cont_val, op, ...) \
+({ \
+ int __ret = -EINVAL; \
+ typeof(result) __r; \
+ \
+ for (const struct fwnode_handle *__node = n; \
+ !IS_ERR_OR_NULL(__node); \
+ __node = __node->secondary) { \
+ if (!__node->ops || !__node->ops->op) { \
+ __ret = -ENXIO; \
+ continue; \
+ } \
+ __r = __node->ops->op(__node, ## __VA_ARGS__); \
+ if (__r != cont_val) { \
+ result = __r; \
+ __ret = 0; \
+ break; \
+ } \
+ } \
+ __ret; \
+})
+
struct fwnode_handle *__dev_fwnode(struct device *dev)
{
return IS_ENABLED(CONFIG_OF) && dev->of_node ?
@@ -57,16 +79,14 @@ EXPORT_SYMBOL_GPL(device_property_present);
bool fwnode_property_present(const struct fwnode_handle *fwnode,
const char *propname)
{
+ int error;
bool ret;
- if (IS_ERR_OR_NULL(fwnode))
+ error = FWNODE_ITERATE(fwnode, ret, false, property_present, propname);
+ if (error)
return false;
- ret = fwnode_call_bool_op(fwnode, property_present, propname);
- if (ret)
- return ret;
-
- return fwnode_call_bool_op(fwnode->secondary, property_present, propname);
+ return ret;
}
EXPORT_SYMBOL_GPL(fwnode_property_present);
@@ -259,18 +279,15 @@ static int fwnode_property_read_int_array(const struct fwnode_handle *fwnode,
unsigned int elem_size, void *val,
size_t nval)
{
+ int error;
int ret;
- if (IS_ERR_OR_NULL(fwnode))
- return -EINVAL;
-
- ret = fwnode_call_int_op(fwnode, property_read_int_array, propname,
- elem_size, val, nval);
- if (ret != -EINVAL)
- return ret;
+ error = FWNODE_ITERATE(fwnode, ret, -EINVAL, property_read_int_array,
+ propname, elem_size, val, nval);
+ if (error)
+ return error;
- return fwnode_call_int_op(fwnode->secondary, property_read_int_array, propname,
- elem_size, val, nval);
+ return ret;
}
/**
@@ -414,18 +431,15 @@ int fwnode_property_read_string_array(const struct fwnode_handle *fwnode,
const char *propname, const char **val,
size_t nval)
{
+ int error;
int ret;
- if (IS_ERR_OR_NULL(fwnode))
- return -EINVAL;
-
- ret = fwnode_call_int_op(fwnode, property_read_string_array, propname,
- val, nval);
- if (ret != -EINVAL)
- return ret;
+ error = FWNODE_ITERATE(fwnode, ret, -EINVAL, property_read_string_array,
+ propname, val, nval);
+ if (error)
+ return error;
- return fwnode_call_int_op(fwnode->secondary, property_read_string_array, propname,
- val, nval);
+ return ret;
}
EXPORT_SYMBOL_GPL(fwnode_property_read_string_array);
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