linux-kernel - Re: [PATCH] soc: aspeed: Add NULL pointer check in aspeed_lpc_enable

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Message-ID: <CALGdzurifZaqatjGRZGxA4FyNBHOYJdVXpKHSM4hQdA3qZtYvQ@mail.gmail.com>
Date: Wed, 12 Feb 2025 19:50:49 -0600
From: Chenyuan Yang <chenyuan0y@...il.com>
To: Andrew Jeffery <andrew@...econstruct.com.au>
Cc: joel@....id.au, richardcochran@...il.com, 
	linux-arm-kernel@...ts.infradead.org, linux-aspeed@...ts.ozlabs.org, 
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] soc: aspeed: Add NULL pointer check in aspeed_lpc_enable_snoop()

Hi Andrew,

I've drafted the following patch to address the resource cleanup issue:

```
 drivers/soc/aspeed/aspeed-lpc-snoop.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/soc/aspeed/aspeed-lpc-snoop.c
b/drivers/soc/aspeed/aspeed-lpc-snoop.c
index 9ab5ba9cf1d6..4988144aba88 100644
--- a/drivers/soc/aspeed/aspeed-lpc-snoop.c
+++ b/drivers/soc/aspeed/aspeed-lpc-snoop.c
@@ -200,11 +200,15 @@ static int aspeed_lpc_enable_snoop(struct
aspeed_lpc_snoop *lpc_snoop,
  lpc_snoop->chan[channel].miscdev.minor = MISC_DYNAMIC_MINOR;
  lpc_snoop->chan[channel].miscdev.name =
  devm_kasprintf(dev, GFP_KERNEL, "%s%d", DEVICE_NAME, channel);
+ if (!lpc_snoop->chan[channel].miscdev.name) {
+ rc = -ENOMEM;
+ goto free_fifo;
+ }
  lpc_snoop->chan[channel].miscdev.fops = &snoop_fops;
  lpc_snoop->chan[channel].miscdev.parent = dev;
  rc = misc_register(&lpc_snoop->chan[channel].miscdev);
  if (rc)
- return rc;
+ goto free_name;

  /* Enable LPC snoop channel at requested port */
  switch (channel) {
@@ -221,7 +225,8 @@ static int aspeed_lpc_enable_snoop(struct
aspeed_lpc_snoop *lpc_snoop,
  hicrb_en = HICRB_ENSNP1D;
  break;
  default:
- return -EINVAL;
+ rc = -EINVAL;
+ goto free_misc;
  }

  regmap_update_bits(lpc_snoop->regmap, HICR5, hicr5_en, hicr5_en);
@@ -232,6 +237,14 @@ static int aspeed_lpc_enable_snoop(struct
aspeed_lpc_snoop *lpc_snoop,
  hicrb_en, hicrb_en);

  return rc;
+
+free_misc:
+ misc_deregister(&lpc_snoop->chan[channel].miscdev);
+free_name:
+ kfree(lpc_snoop->chan[channel].miscdev.name);
+free_fifo:
+ kfifo_free(&lpc_snoop->chan[channel].fifo);
+ return rc;
 }
```

I have a couple of questions regarding the cleanup order:

1. Do we need to call misc_deregister() in this case, considering that
the registration happens before return -EINVAL?
2. If misc_deregister() is required, is there a specific order we
should follow when calling misc_deregister() and
kfree(lpc_snoop->chan[channel].miscdev.name);?

-Chenyuan

On Wed, Feb 12, 2025 at 7:39 PM Andrew Jeffery
<andrew@...econstruct.com.au> wrote:
>
> On Wed, 2025-02-12 at 19:37 -0600, Chenyuan Yang wrote:
> > Hi Andrew,
> >
> > Thanks for your prompt reply!
> >
> > On Wed, Feb 12, 2025 at 6:21 PM Andrew Jeffery
> > <andrew@...econstruct.com.au> wrote:
> > >
> > > Hi Chenyuan,
> > >
> > > On Wed, 2025-02-12 at 15:25 -0600, Chenyuan Yang wrote:
> > > > lpc_snoop->chan[channel].miscdev.name could be NULL, thus,
> > > > a pointer check is added to prevent potential NULL pointer
> > > > dereference.
> > > > This is similar to the fix in commit 3027e7b15b02
> > > > ("ice: FiI am cx some null pointer dereference issues in ice_ptp.c").
> > > >
> > > > This issue is found by our static analysis tool.
> > > >
> > > > Signed-off-by: Chenyuan Yang <chenyuan0y@...il.com>
> > > > ---
> > > >  drivers/soc/aspeed/aspeed-lpc-snoop.c | 2 ++
> > > >  1 file changed, 2 insertions(+)
> > > >
> > > > diff --git a/drivers/soc/aspeed/aspeed-lpc-snoop.c
> > > > b/drivers/soc/aspeed/aspeed-lpc-snoop.c
> > > > index 9ab5ba9cf1d6..376b3a910797 100644
> > > > --- a/drivers/soc/aspeed/aspeed-lpc-snoop.c
> > > > +++ b/drivers/soc/aspeed/aspeed-lpc-snoop.c
> > > > @@ -200,6 +200,8 @@ static int aspeed_lpc_enable_snoop(struct
> > > > aspeed_lpc_snoop *lpc_snoop,
> > > >         lpc_snoop->chan[channel].miscdev.minor = MISC_DYNAMIC_MINOR;
> > > >         lpc_snoop->chan[channel].miscdev.name =
> > > >                 devm_kasprintf(dev, GFP_KERNEL, "%s%d", DEVICE_NAME,
> > > > channel);
> > > > +       if (!lpc_snoop->chan[channel].miscdev.name)
> > > > +               return -ENOMEM;
> > >
> > > This introduces yet another place where the driver leaks resources in
> > > an error path (in this case, the channel kfifo). The misc device also
> > > gets leaked later on. It would be nice to address those first so that
> > > handling this error can take the appropriate cleanup path.
> > >
> > > Andrew
> >
> > It seems that the `aspeed_lpc_enable_snoop()` function originally does
> > not have a cleanup path. For example, if `misc_register` fails, the
> > function directly returns rc without performing any cleanup.
> > Similarly, when the `channel` has its default value, the function
> > simply returns -EINVAL.
> >
> > Given this, I am wondering whether it would be a good idea to
> > introduce a cleanup path. If so, should we ensure cleanup for all
> > possible exit points?
>
> Yes please!
>
> Thanks,
>
> Andrew
>