[PATCH 1/2] netfilter: correct parsing of continuation lines in SIP headers

[PATCH 1/2] netfilter: correct parsing of continuation lines in SIP headers

[Marco Angaroni]

Current parsing methods for SIP headers do not properly manage
continuation lines: in case of Call-ID header the first character of
Call-ID header value is truncated. As a result IPVS SIP persistence
engine hashes over a call-id that is not exactly the one present in
the originale message.

Example: "Call-ID: \r\n abcdeABCDE1234"
results in extracted call-id equal to "bcdeABCDE1234".

In above example Call-ID is represented as a string in C language.
Obviously in real message the first bytes after colon (":") are
"20 0d 0a 20".

Proposed fix is in nf_conntrack_sip module.
Since sip_follow_continuation() function walks past the leading
spaces or tabs of the continuation line, sip_skip_whitespace()
should simply return the ouput of sip_follow_continuation().
Otherwise another iteration of the for loop is done and dptr
is incremented by one pointing to the second character of the
first word in the header.

Below is an extract of relevant SIP ABNF syntax.

Call-ID  =  ( "Call-ID" / "i" ) HCOLON callid
callid   =  word [ "@" word ]

HCOLON  =  *( SP / HTAB ) ":" SWS
SWS     =  [LWS] ; sep whitespace
LWS     =  [*WSP CRLF] 1*WSP ; linear whitespace
WSP     =  SP / HTAB
word    =  1*(alphanum / "-" / "." / "!" / "%" / "*" /
           "_" / "+" / "`" / "'" / "~" /
           "(" / ")" / "<" / ">" /
           ":" / "\" / DQUOTE /
           "/" / "[" / "]" / "?" /
           "{" / "}" )

Signed-off-by: Marco Angaroni <marcoangaroni@gmail.com>
---
 net/netfilter/nf_conntrack_sip.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/netfilter/nf_conntrack_sip.c b/net/netfilter/nf_conntrack_sip.c
index 8971109..c23249e 100644
--- a/net/netfilter/nf_conntrack_sip.c
+++ b/net/netfilter/nf_conntrack_sip.c
@@ -335,8 +335,7 @@ static const char *sip_skip_whitespace(const char *dptr, const char *limit)
 		if (*dptr != '\r' && *dptr != '\n')
 			break;
 		dptr = sip_follow_continuation(dptr, limit);
-		if (dptr == NULL)
-			return NULL;
+		return dptr;
 	}
 	return dptr;
 }
-- 
1.8.3.1

Re: [PATCH 1/2] netfilter: correct parsing of continuation lines in SIP headers

[Pablo Neira Ayuso]

On Tue, Aug 30, 2016 at 06:48:19PM +0200, Marco Angaroni wrote:
> Current parsing methods for SIP headers do not properly manage
> continuation lines: in case of Call-ID header the first character of
> Call-ID header value is truncated. As a result IPVS SIP persistence
> engine hashes over a call-id that is not exactly the one present in
> the originale message.
> 
> Example: "Call-ID: \r\n abcdeABCDE1234"
> results in extracted call-id equal to "bcdeABCDE1234".
> 
> In above example Call-ID is represented as a string in C language.
> Obviously in real message the first bytes after colon (":") are
> "20 0d 0a 20".
> 
> Proposed fix is in nf_conntrack_sip module.
> Since sip_follow_continuation() function walks past the leading
> spaces or tabs of the continuation line, sip_skip_whitespace()
> should simply return the ouput of sip_follow_continuation().
> Otherwise another iteration of the for loop is done and dptr
> is incremented by one pointing to the second character of the
> first word in the header.
> 
> Below is an extract of relevant SIP ABNF syntax.
> 
> Call-ID  =  ( "Call-ID" / "i" ) HCOLON callid
> callid   =  word [ "@" word ]
> 
> HCOLON  =  *( SP / HTAB ) ":" SWS
> SWS     =  [LWS] ; sep whitespace
> LWS     =  [*WSP CRLF] 1*WSP ; linear whitespace
> WSP     =  SP / HTAB
> word    =  1*(alphanum / "-" / "." / "!" / "%" / "*" /
>            "_" / "+" / "`" / "'" / "~" /
>            "(" / ")" / "<" / ">" /
>            ":" / "\" / DQUOTE /
>            "/" / "[" / "]" / "?" /
>            "{" / "}" )
> 
> Signed-off-by: Marco Angaroni <marcoangaroni@gmail.com>
> ---
>  net/netfilter/nf_conntrack_sip.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/net/netfilter/nf_conntrack_sip.c b/net/netfilter/nf_conntrack_sip.c
> index 8971109..c23249e 100644
> --- a/net/netfilter/nf_conntrack_sip.c
> +++ b/net/netfilter/nf_conntrack_sip.c
> @@ -335,8 +335,7 @@ static const char *sip_skip_whitespace(const char *dptr, const char *limit)
>  		if (*dptr != '\r' && *dptr != '\n')
>  			break;
>  		dptr = sip_follow_continuation(dptr, limit);
> -		if (dptr == NULL)
> -			return NULL;
> +		return dptr;

I'd suggest you use the break statement here instead, ie.

-		if (dptr == NULL)
-			return NULL;
+		break;

>  	}
>  	return dptr;
>  }
> -- 
> 1.8.3.1
> 
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Re: [PATCH 1/2] netfilter: correct parsing of continuation lines in SIP headers

[Pablo Neira Ayuso]

On Tue, Aug 30, 2016 at 06:48:19PM +0200, Marco Angaroni wrote:
> Current parsing methods for SIP headers do not properly manage
> continuation lines: in case of Call-ID header the first character of
> Call-ID header value is truncated. As a result IPVS SIP persistence
> engine hashes over a call-id that is not exactly the one present in
> the originale message.
> 
> Example: "Call-ID: \r\n abcdeABCDE1234"
> results in extracted call-id equal to "bcdeABCDE1234".
> 
> In above example Call-ID is represented as a string in C language.
> Obviously in real message the first bytes after colon (":") are
> "20 0d 0a 20".
> 
> Proposed fix is in nf_conntrack_sip module.
> Since sip_follow_continuation() function walks past the leading
> spaces or tabs of the continuation line, sip_skip_whitespace()
> should simply return the ouput of sip_follow_continuation().
> Otherwise another iteration of the for loop is done and dptr
> is incremented by one pointing to the second character of the
> first word in the header.
> 
> Below is an extract of relevant SIP ABNF syntax.
> 
> Call-ID  =  ( "Call-ID" / "i" ) HCOLON callid
> callid   =  word [ "@" word ]
> 
> HCOLON  =  *( SP / HTAB ) ":" SWS
> SWS     =  [LWS] ; sep whitespace
> LWS     =  [*WSP CRLF] 1*WSP ; linear whitespace
> WSP     =  SP / HTAB
> word    =  1*(alphanum / "-" / "." / "!" / "%" / "*" /
>            "_" / "+" / "`" / "'" / "~" /
>            "(" / ")" / "<" / ">" /
>            ":" / "\" / DQUOTE /
>            "/" / "[" / "]" / "?" /
>            "{" / "}" )

Applied the mangled version, using break; instead.

Thanks!