linux-kernel - AW: [PATCH] soc: aspeed: fix a ternary sign expansion bug

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ebe4a1a6dd0748e28e6ca19aec20223e@bfs.de>
Date:   Fri, 23 Apr 2021 11:03:30 +0000
From:   Walter Harms <wharms@....de>
To:     David Laight <David.Laight@...LAB.COM>,
        'Sergey Organov' <sorganov@...il.com>
CC:     'Dan Carpenter' <dan.carpenter@...cle.com>,
        Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>,
        "Chia-Wei, Wang" <chiawei_wang@...eedtech.com>,
        Jae Hyun Yoo <jae.hyun.yoo@...el.com>,
        "John Wang" <wangzhiqiang.bj@...edance.com>,
        Brad Bishop <bradleyb@...ziesquirrel.com>,
        Patrick Venture <venture@...gle.com>,
        "Benjamin Fair" <benjaminfair@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Robert Lippert <rlippert@...gle.com>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>
Subject: AW: [PATCH] soc: aspeed: fix a ternary sign expansion bug

as indepentent observer,
i would go for Dans solution:

ret = kfifo_to_user();
/* if an error occurs just return */
if (ret)
   return ret;

/* otherwise return the copied number of bytes */

return copied;

there is no need for any deeper language knowledge,

jm2c
re,
 wh
________________________________________
Von: David Laight <David.Laight@...LAB.COM>
Gesendet: Freitag, 23. April 2021 12:54:59
An: 'Sergey Organov'
Cc: 'Dan Carpenter'; Joel Stanley; Andrew Jeffery; Chia-Wei, Wang; Jae Hyun Yoo; John Wang; Brad Bishop; Patrick Venture; Benjamin Fair; Greg Kroah-Hartman; Robert Lippert; linux-aspeed@...ts.ozlabs.org; linux-kernel@...r.kernel.org; kernel-janitors@...r.kernel.org
Betreff: RE: [PATCH] soc: aspeed: fix a ternary sign expansion bug

WARNUNG: Diese E-Mail kam von außerhalb der Organisation. Klicken Sie nicht auf Links oder öffnen Sie keine Anhänge, es sei denn, Sie kennen den/die Absender*in und wissen, dass der Inhalt sicher ist.


From: Sergey Organov
> Sent: 23 April 2021 11:46
>
> David Laight <David.Laight@...LAB.COM> writes:
>
> > From: Dan Carpenter
> >> Sent: 22 April 2021 10:12
> >>
> >> The intent here was to return negative error codes but it actually
> >> returns positive values.  The problem is that type promotion with
> >> ternary operations is quite complicated.
> >>
> >> "ret" is an int.  "copied" is a u32.  And the snoop_file_read() function
> >> returns long.  What happens is that "ret" is cast to u32 and becomes
> >> positive then it's cast to long and it's still positive.
> >>
> >> Fix this by removing the ternary so that "ret" is type promoted directly
> >> to long.
> >>
> >> Fixes: 3772e5da4454 ("drivers/misc: Aspeed LPC snoop output using misc chardev")
> >> Signed-off-by: Dan Carpenter <dan.carpenter@...cle.com>
> >> ---
> >>  drivers/soc/aspeed/aspeed-lpc-snoop.c | 4 +++-
> >>  1 file changed, 3 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/soc/aspeed/aspeed-lpc-snoop.c b/drivers/soc/aspeed/aspeed-lpc-snoop.c
> >> index 210455efb321..eceeaf8dfbeb 100644
> >> --- a/drivers/soc/aspeed/aspeed-lpc-snoop.c
> >> +++ b/drivers/soc/aspeed/aspeed-lpc-snoop.c
> >> @@ -94,8 +94,10 @@ static ssize_t snoop_file_read(struct file *file, char __user *buffer,
> >>                    return -EINTR;
> >>    }
> >>    ret = kfifo_to_user(&chan->fifo, buffer, count, &copied);
> >> +  if (ret)
> >> +          return ret;
> >>
> >> -  return ret ? ret : copied;
> >> +  return copied;
> >
> > I wonder if changing it to:
> >     return ret ? ret + 0L : copied;
> >
> > Might make people think in the future and not convert it back
> > as an 'optimisation'.
>
> It rather made me think: "what the heck is going on here?!"
>
> Shouldn't it better be:
>
>       return ret ? ret : (long)copied;
>
> or even:
>
>         return ret ?: (long)copied;

Or change the return type to int ?

The problem is that ?: doesn't behave the way most people expect.
The two possible values have to be converted to the same type.

Together with the broken decision of the original ANSI C committee
to change from K&R's 'sign preserving' to 'value preserving'
integer promotions causes grief here and elsewhere.
(Not no mention breaking existing code!)

        David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)