linux-kernel - Re: [PATCH 1/1] module: fix sprintf format specifier in param_get

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Date:	Wed, 07 Aug 2013 13:31:30 +0200
From:	Michal Nazarewicz <mina86@...a86.com>
To:	Rusty Russell <rusty@...tcorp.com.au>,
	Christoph Jaeger <christophjaeger@...ux.com>
Cc:	linux-kernel@...r.kernel.org,
	Dmitry Tarnyagin <dmitry.tarnyagin@...kless.no>,
	Jon Mason <jon.mason@...el.com>, tech.support@...lex.com,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH 1/1] module: fix sprintf format specifier in param_get_byte()

On Wed, Aug 07 2013, Rusty Russell wrote:
> Christoph Jaeger <christophjaeger@...ux.com> writes:
>> In param_get_byte(), to which the macro STANDARD_PARAM_DEF(byte, ...) expands,
>> "%c" is used to print an unsigned char. So it gets printed as a character what
>> is not intended here. Use "%hhu" instead.
>>
>> Signed-off-by: Christoph Jaeger <christophjaeger@...ux.com>

Acked-by: Michal Nazarewicz <mina86@...a86.com>

for g_ffs.c:

> drivers/usb/gadget/g_ffs.c:95:module_param_named(bDeviceClass,    gfs_dev_desc.bDeviceClass,    byte,   0644);
> drivers/usb/gadget/g_ffs.c:97:module_param_named(bDeviceSubClass, gfs_dev_desc.bDeviceSubClass, byte,   0644);
> drivers/usb/gadget/g_ffs.c:99:module_param_named(bDeviceProtocol, gfs_dev_desc.bDeviceProtocol, byte,   0644);

I don't think it breaks anything for g_ffs since those properties are
most likely write-only and I don't expect many people reading them.

>> ---
>>  kernel/params.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/params.c b/kernel/params.c
>> index 440e65d..59f7ac7 100644
>> --- a/kernel/params.c
>> +++ b/kernel/params.c
>> @@ -252,7 +252,7 @@ int parse_args(const char *doing,
>>  	EXPORT_SYMBOL(param_ops_##name)
>>  
>>  
>> -STANDARD_PARAM_DEF(byte, unsigned char, "%c", unsigned long, strict_strtoul);
>> +STANDARD_PARAM_DEF(byte, unsigned char, "%hhu", unsigned long, strict_strtoul);
>>  STANDARD_PARAM_DEF(short, short, "%hi", long, strict_strtol);
>>  STANDARD_PARAM_DEF(ushort, unsigned short, "%hu", unsigned long, strict_strtoul);

Actually, are those “h” specifiers even necessary?  I'm fairly certain
that “%u” for byte, “%i” for short, and “%u” for ushort would work just
fine since the argument gets promoted to (unsigned) int anyway and
indeed vsnprintf reads an int for all those types.

>>  STANDARD_PARAM_DEF(int, int, "%i", long, strict_strtol);

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +----<email/xmpp: mpn@...gle.com>--------------ooO--(_)--Ooo--

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