[PATCH] staging: speakup: kobjects.c: fix char argument to %02x

[PATCH] staging: speakup: kobjects.c: fix char argument to %02x

[Rasmus Villemoes]

If char is signed and ch happens to be negative, printing ch with
"%02x" will not do as intended (when ch is -19, one will get
"ffffffed"). Fix that by masking with 0xff.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
 drivers/staging/speakup/kobjects.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/staging/speakup/kobjects.c b/drivers/staging/speakup/kobjects.c
index fdfeb42b2b8f..8b88f03e266b 100644
--- a/drivers/staging/speakup/kobjects.c
+++ b/drivers/staging/speakup/kobjects.c
@@ -567,7 +567,7 @@ ssize_t spk_var_show(struct kobject *kobj, struct kobj_attribute *attr,
 				if (ch >= ' ' && ch < '~')
 					*cp1++ = ch;
 				else
-					cp1 += sprintf(cp1, "\\x%02x", ch);
+					cp1 += sprintf(cp1, "\\x%02x", ch & 0xff);
 			}
 			*cp1++ = '"';
 			*cp1++ = '\n';
-- 
2.6.1

Re: [PATCH] staging: speakup: kobjects.c: fix char argument to %02x

[Joe Perches]

On Sun, 2015-12-06 at 01:05 +0100, Rasmus Villemoes wrote:
> If char is signed and ch happens to be negative, printing ch with
> "%02x" will not do as intended (when ch is -19, one will get
> "ffffffed"). Fix that by masking with 0xff.

I presume there are a lot of these in the kernel.
Did you use a tool to find this or just inspection?

Re: [PATCH] staging: speakup: kobjects.c: fix char argument to %02x

[Rasmus Villemoes]

On Sun, Dec 06 2015, Joe Perches <joe@perches.com> wrote:

> On Sun, 2015-12-06 at 01:05 +0100, Rasmus Villemoes wrote:
>> If char is signed and ch happens to be negative, printing ch with
>> "%02x" will not do as intended (when ch is -19, one will get
>> "ffffffed"). Fix that by masking with 0xff.
>
> I presume there are a lot of these in the kernel.
> Did you use a tool to find this or just inspection?

Initially I just used coccinelle, for the most obvious candidates (with
--include-headers-for-types):

@r depends on !patch@
char c;
@@
* \( sprintf \| snprintf \| scnprintf \) (..., c, ...)

That gives lots of false positives (arguments to %c), but it's not too
bad piping to less, searching for "%[0.]2[xX]", and then checking
manually.

I'm now doing a much wider range of printf functions, but it's really
past my bedtime, so feel free to pick up the ball :-)

Rasmus

Re: [PATCH] staging: speakup: kobjects.c: fix char argument to %02x

[Joe Perches]

On Sun, 2015-12-06 at 01:21 +0100, Rasmus Villemoes wrote:
> On Sun, Dec 06 2015, Joe Perches <joe@perches.com> wrote:
> 
> > On Sun, 2015-12-06 at 01:05 +0100, Rasmus Villemoes wrote:
> > > If char is signed and ch happens to be negative, printing ch with
> > > "%02x" will not do as intended (when ch is -19, one will get
> > > "ffffffed"). Fix that by masking with 0xff.
> > 
> > I presume there are a lot of these in the kernel.
> > Did you use a tool to find this or just inspection?
> 
> Initially I just used coccinelle, for the most obvious candidates
> (with
> --include-headers-for-types):
> 
> @r depends on !patch@
> char c;
> @@
> * \( sprintf \| snprintf \| scnprintf \) (..., c, ...)
> 
> That gives lots of false positives (arguments to %c), but it's not
> too
> bad piping to less, searching for "%[0.]2[xX]", and then checking
> manually.
> 
> I'm now doing a much wider range of printf functions, but it's really
> past my bedtime, so feel free to pick up the ball :-)
> 

Thanks, but no thanks.  It's your ball.  Enjoy...

You might consider looking for s8 and s16 emitted as %u too.

Re: [PATCH] staging: speakup: kobjects.c: fix char argument to %02x

[Andy Shevchenko]

On Sun, Dec 6, 2015 at 2:05 AM, Rasmus Villemoes
<linux@rasmusvillemoes.dk> wrote:
> If char is signed and ch happens to be negative, printing ch with
> "%02x" will not do as intended (when ch is -19, one will get
> "ffffffed"). Fix that by masking with 0xff.
>
> Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
> ---
>  drivers/staging/speakup/kobjects.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/staging/speakup/kobjects.c b/drivers/staging/speakup/kobjects.c
> index fdfeb42b2b8f..8b88f03e266b 100644
> --- a/drivers/staging/speakup/kobjects.c
> +++ b/drivers/staging/speakup/kobjects.c
> @@ -567,7 +567,7 @@ ssize_t spk_var_show(struct kobject *kobj, struct kobj_attribute *attr,
>                                 if (ch >= ' ' && ch < '~')
>                                         *cp1++ = ch;
>                                 else
> -                                       cp1 += sprintf(cp1, "\\x%02x", ch);
> +                                       cp1 += sprintf(cp1, "\\x%02x", ch & 0xff);

Have you considered to use string_escape_str()?


This one clearly looks like ESCAPE_HEX.

>                         }
>                         *cp1++ = '"';
>                         *cp1++ = '\n';
> --
> 2.6.1
>
> --
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-- 
With Best Regards,
Andy Shevchenko