linux-kernel - Re: [PATCH] eeepc-laptop: remove possible use of uninitialized value

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Date:	Thu, 4 Sep 2014 07:10:41 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Frans Klaver <fransklaver@...il.com>
Cc:	Darren Hart <dvhart@...radead.org>,
	Corentin Chary <corentin.chary@...il.com>,
	Matthew Garrett <matthew.garrett@...ula.com>,
	acpi4asus-user <acpi4asus-user@...ts.sourceforge.net>,
	platform-driver-x86 <platform-driver-x86@...r.kernel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] eeepc-laptop: remove possible use of uninitialized value

On Thu, Sep 04, 2014 at 08:46:40AM +0200, Frans Klaver wrote:
> On Thu, Sep 4, 2014 at 3:14 AM, Greg Kroah-Hartman
> <gregkh@...uxfoundation.org> wrote:
> > On Wed, Sep 03, 2014 at 05:49:47PM -0700, Darren Hart wrote:
> >> On Thu, Sep 04, 2014 at 12:53:25AM +0200, Frans Klaver wrote:
> >> > In store_sys_acpi, if count equals zero, or parse_arg()s sscanf call
> >> > fails, 'value' remains possibly uninitialized. In that case 'value'
> >> > shouldn't be used to produce the store_sys_acpi()s return value.
> 
> Here I should probably remove either 'the' or the 's' after store_sys_acpi().
> 
> 
> >> > Only test the return value of set_acpi() if we can actually call it.
> >> > Return rv otherwise.
> >> >
> >> > Signed-off-by: Frans Klaver <fransklaver@...il.com>
> >> > ---
> >> >  drivers/platform/x86/eeepc-laptop.c | 8 ++++----
> >> >  1 file changed, 4 insertions(+), 4 deletions(-)
> >> >
> >> > diff --git a/drivers/platform/x86/eeepc-laptop.c b/drivers/platform/x86/eeepc-laptop.c
> >> > index bd533c2..41f12ba 100644
> >> > --- a/drivers/platform/x86/eeepc-laptop.c
> >> > +++ b/drivers/platform/x86/eeepc-laptop.c
> >> > @@ -279,10 +279,10 @@ static ssize_t store_sys_acpi(struct device *dev, int cm,
> >> >     int rv, value;
> >> >
> >> >     rv = parse_arg(buf, count, &value);
> >> > -   if (rv > 0)
> >> > -           value = set_acpi(eeepc, cm, value);
> >>
> >> That was rather horrible wasn't it? :-)
> >>
> >> > -   if (value < 0)
> >> > -           return -EIO;
> >> > +   if (rv > 0) {
> >> > +           if (set_acpi(eeepc, cm, value) < 0)
> >> > +                   return -EIO;
> >>
> >> Is there a compelling reason not to propogate the return code of set_acpi?
> >> (ENODEV specifically). I see -EIO in Documentation/filesystems/sysfs.txt, but
> >> it's used by default if the show() pointer is NULL (for example), but otherwise
> >> propogates the error.
> >>
> >> Specifically it states:
> >>
> >> - show() or store() can always return errors. If a bad value comes
> >>   through, be sure to return an error.
> >>
> >> Greg, does this need to be -EIO? or is returning someting like ENODEV preferable
> >> if it more accurately reflects the error?
> >
> > Just return the value of set_acpi() and you should be fine.
> 
> According to 6dff29b63a5bf2eaf3313cb8a84f0b7520c43401 "eeepc-laptop:
> disp attribute should be write-only" it should be -EIO. -ENODEV would
> be misleading.

If something is "write only" then there should not be a store function
for it at all, the file should not be marked as writable, to prevent
anything from ever being written to it at the higher-level filesystem
layer, and never get down to the driver layer...

thanks,

greg k-h
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