linux-kernel - Re: [PATCH 1/2] thunderbolt: Fix a leak in tb_retimer

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Date:   Mon, 29 Mar 2021 10:02:20 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
Cc:     Andreas Noever <andreas.noever@...il.com>,
        Kranthi Kuntala <kranthi.kuntala@...el.com>,
        Michael Jamet <michael.jamet@...el.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Yehezkel Bernat <YehezkelShB@...il.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 1/2] thunderbolt: Fix a leak in tb_retimer_add()

On Mon, Mar 29, 2021 at 09:07:18AM +0300, Dan Carpenter wrote:
> After the device_register() succeeds, then the correct way to clean up
> is to call device_unregister().  The unregister calls both device_del()
> and device_put().  Since this code was only device_del() it results in
> a memory leak.
> 
> Fixes: dacb12877d92 ("thunderbolt: Add support for on-board retimers")
> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> ---
> This is from a new static checker warning.  Not tested.  With new
> warnings it's also possible that I have misunderstood something
> fundamental so review carefully etc.

It looks OK to me

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

This also highlights the code has an ordering issue too, it calls
device_register() then goes to do tb_retimer_nvm_add() however
device_register() makes sysfs attributes visible before the rt->nvm is
initialized and this:

static ssize_t nvm_authenticate_store(struct device *dev,
	struct device_attribute *attr, const char *buf, size_t count)
{
	if (!rt->nvm) {

Isn't strong enough to close the potential racing. The nvm should be
setup before device_register and all the above tests in the sysfs
deleted so we can rely on the CPU barriers built into
device_register() for correctness.

[which is a general tip, be very suspicious if device_register() is
being error unwound]

Jason