linux-kernel - Re: [PATCH 2/2] tracing/filters: use strcmp() instead of strncmp()

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Date:	Mon, 01 Jun 2009 13:45:47 +0800
From:	Li Zefan <lizf@...fujitsu.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	Tom Zanussi <tzanussi@...il.com>, Ingo Molnar <mingo@...e.hu>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] tracing/filters: use strcmp() instead of strncmp()

>>>> I don't think there's any security issue. It's irrelevant how big the user-input
>>>> strings are. The point is those strings are guaranteed to be NULL-terminated.
>>>> Am I missing something?
>>>>
>>>> And I don't think it's necessary to make 2 patches that each patch converts
>>>> one strncmp to strcmp. But maybe it's better to improve this changelog?
>>> Hmm, you must be right, indeed they seem to be guaranted beeing NULL-terminated
>>> strings.
>>>
>> Sorry, I was wrong. :(
>>
>> Though the user-input strings are guaranted to be NULL-terminated, strings
>> generated by TRACE_EVENT might not.
>>
>> We define static strings this way:
>> 	TP_struct(
>> 		__array(char, foo, LEN)
>> 	)
>> But foo is not necessarily a string, though I doubt someone will use it
>> as non-string char array.
> 
> 
> Yeah, but the user defined comparison operand is NULL terminated.
> So the strcmp will stop at this boundary.
> 

The user input string is NULL terminated and is limited to MAX_FILTER_STR_VAL,
and it's strcmp() not strcpy(), but it's still unsafe. No?

	cmp = strcmp(addr, pred->str_val);

If addr is not NULL-terminated string but char array, and length of
str_val > length of addr, then we'll be exceeding the boundary of the
array.

> 
>  
>> Dynamic string is fine, because assign_str() makes it NULL-terminated.
>>
>> So we can use strcmp() for dynamic strings, but we'd better use strncmp() for
>> static string.
>>
>>
> 
> 
> 
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