Re: Genfscon 'dash' issue

[Joshua Brindle <method@manicmethod.com>]

Stephen Smalley wrote:
> On Tue, 2008-10-14 at 02:00 +0000, korkishko Tymur wrote:
>   
>> I have checked policy_parse.y. It has following rule for genfscon:
>>  
>> genfs_context_def	: GENFSCON identifier path '-' identifier security_context_def
>> 	{if (define_genfs_context(1)) return -1;}
>> 	| GENFSCON identifier path '-' '-' {insert_id("-", 0);} security_context_def
>> 	{if (define_genfs_context(1)) return -1;}
>> 	 | GENFSCON identifier path security_context_def
>> 	{if (define_genfs_context(0)) return -1;} 
>>
>> The rule for path definition (in policy_scan.l) has already included '-' (dash):
>>
>> "/"({alnum}|[_.-/])*	        { return(PATH); } 
>>
>> In my understanding (maybe wrong), path is parsed first (and path might include '-') and only then separate '-' is parsed. 
>> But it still produces an error if path definition is correct and includes '-'.
>>
>> Any ideas/patches how to fix grammar rules are welcomed.
>>     
>
> This looks like a bug in policy_scan.l - we are not escaping (via
> backslash) special characters in the pattern and thus the "-" (dash) is
> being interpreted rather than taken literally.  The same would seemingly
> apply for "." (dot), and would seem relevant not only to PATH but also
> for IDENTIFIER.  The patch below seems to fix this issue for me:
>
> diff --git a/checkpolicy/policy_scan.l b/checkpolicy/policy_scan.l
> index 9bc6e10..b55c659 100644
> --- a/checkpolicy/policy_scan.l
> +++ b/checkpolicy/policy_scan.l
> @@ -207,8 +207,8 @@ policycap |
>  POLICYCAP			{ return(POLICYCAP); }
>  permissive |
>  PERMISSIVE			{ return(PERMISSIVE); }
> -"/"({alnum}|[_.-/])*	        { return(PATH); }
> -{letter}({alnum}|[_-])*([.]?({alnum}|[_-]))*	{ return(IDENTIFIER); }
> +"/"({alnum}|[_\.\-/])*	        { return(PATH); }
> +{letter}({alnum}|[_\-])*([\.]?({alnum}|[_\-]))*	{ return(IDENTIFIER); }
>  {digit}+                        { return(NUMBER); }
>  {digit}{1,3}(\.{digit}{1,3}){3}    { return(IPV4_ADDR); }
>  {hexval}{0,4}":"{hexval}{0,4}":"({hexval}|[:.])*  { return(IPV6_ADDR); }
>
>   
It looks like I merged this a little hastily. According to the regex manual:

Character ranges can also be included in a character set, by writing two 
characters with a - between them. Thus, [a-z] matches any lower-case 
letter. Ranges may be intermixed freely with individual characters, as 
in [a-z$%.], which matches any lower case letter or $, % or period.

Note that the usual special characters are not special any more inside a 
character set. A completely different set of special characters exists 
inside character sets: ], - and ^


Therefore \. in a character set means both '\' and '.' are allowed. The 
standard way to add a dash to the character set is to put it last. I'll 
update the patch when I have a chance.


--
This message was distributed to subscribers of the selinux mailing list.
If you no longer wish to subscribe, send mail to majordomo@tycho.nsa.gov with
the words "unsubscribe selinux" without quotes as the message.