[Dnsmasq-discuss] [PATCH] fix bug of FORMERR

[Simon Kelley]

Patch applied, also cleared AA bit.


Many thanks for this.


Cheers,

Simon.

On 27/05/15 20:41, swigger wrote:
> Signed-off-by: swigger <swigger at gmail.com>
> 
> First, sorry for my poor English, hope you can read it.
> 
> My openwrt router at 192.168.1.1 runs dnsmasq.
> There are two DNS ips set automaticly by my ISP.
> 
> When resolving domain names, some times I get a FormErr.
> This is unusual, so I dig this and find a bug.
> 
> When a request is sent to dnsmasq, it forwards to upper DNSs,
> and then , if dns-a replys a ServFail, dnsmasq just forwards
> to dns-b with value of byte 4(base index 1) is 0x82 (HB4_RA|ServFail).
> However, for a normal request, this byte should be 0x00 .
> My ISP's dns-b checks this field and replys a FormErr.
> 
> Here is a proof by tcpdump:
> 11:46:54.377146 IP 121.34.145.201.21657 > 202.96.134.133.53: 18075+ [b2&3=0x182] A? jp.swigger.net. (32)
>         0x0000:  4500 003c f027 4000 4011 eeb7 7922 91c9  E..<.'@. at ...y"..
>         0x0010:  ca60 8685 5499 0035 0028 fbbe 469b 0182  .`..T..5.(..F...
>         0x0020:  0001 0000 0000 0000 026a 7007 7377 6967  .........jp.swig
>         0x0030:  6765 7203 6e65 7400 0001 0001            ger.net.....
> 11:46:54.383814 IP 202.96.134.133.53 > 121.34.145.201.21657: 18075 FormErr 0/0/0 (32)
>         0x0000:  4500 003c 0000 4000 3b11 e3df ca60 8685  E..<.. at .;....`..
>         0x0010:  7922 91c9 0035 5499 0028 7bbf 469b 8181  y"...5T..({.F...
>         0x0020:  0001 0000 0000 0000 026a 7007 7377 6967  .........jp.swig
>         0x0030:  6765 7203 6e65 7400 0001 0001            ger.net.....
> 
> 
> The solution is easy, just reset this field.
> 
> See the following patch.
> 
> ---
>  src/forward.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/src/forward.c b/src/forward.c
> index 74e5ab6..5e14404 100644
> --- a/src/forward.c
> +++ b/src/forward.c
> @@ -770,6 +770,7 @@ void reply_query(int fd, int family, time_t now)
>  	  if ((nn = resize_packet(header, (size_t)n, pheader, plen)))
>  	    {
>  	      header->hb3 &= ~(HB3_QR | HB3_TC);
> +	      header->hb4 &= ~(HB4_RA | HB4_RCODE);
>  	      forward_query(-1, NULL, NULL, 0, header, nn, now, forward, 0, 0);
>  	      return;
>  	    }
>