Syslinux - Sep 2015 - pxelinux tries to load ldlinux.c32 from DHCP server, instead of next-server

On Sat, Sep 12, 2015 at 6:37 PM, Gene Cumm <gene.cumm at gmail.com>
wrote:
> On Sat, Sep 12, 2015 at 10:23 AM, Geert Stappers <stappers at
stappers.nl> wrote:
>> Euh, could this be reviewed:
>>
>> diff --git a/core/fs/pxe/dhcp_option.c b/core/fs/pxe/dhcp_option.c
>> index 8d93a6a..b82e944 100644
>> --- a/core/fs/pxe/dhcp_option.c
>> +++ b/core/fs/pxe/dhcp_option.c
>> @@ -143,8 +143,8 @@ static const struct dhcp_options dhcp_opts[] = {
>>      {15,  local_domain},
>>      {43,  vendor_encaps},
>>      {52,  option_overload},
>> -    {54,  server},
>>      {61,  client_identifier},
>> +    {66,  tftpserver_name},
>>      {67,  bootfile_name},
>>      {97,  uuid_client_identifier},
>>      {209, pxelinux_configfile},
>> @@ -215,7 +215,7 @@ void parse_dhcp_options(const void *option, int
size, uint8_t opt_filter)
>>   * information is present:
>>   *
>>   * MyIP                - client IP address
>> - * server_ip   - boot server IP address
>> + * server_ip   - boot server IP address,  REVIEW ME   FIXME
>>   * net_mask    - network mask
>>   * gate_way    - default gateway router IP
>>   * boot_file   - boot file name
>> @@ -252,4 +252,6 @@ void parse_dhcp(const void *pkt, size_t pkt_len,
int pkt_type)
>>
>>      if (over_load & 2)
>>          parse_dhcp_options(dhcp->sname, 64, 0);
>> +
>> +    /* What about option 66, tftserver_name ?   FIXME */
>>  }
>
> Something like this would be preferable except it's not quite so
> simple.  We'd need to not store BOOTP siaddr before parsing.  Store a
> pointer to the string during parsing if serverip is unset.  After all
> parsing, if the pointer is set, attempt to resolve then set serverip.
> Last, if serverip is not set, copy siaddr to serverip.
Perhaps a more important question is if ANY PXE implementation uses
DHCP option 66 over BOOTP field siaddr.

-- 
-Gene

On Sat, Sep 12, 2015 at 06:56:04PM -0400, Gene Cumm via Syslinux
wrote:
> On Sat, Sep 12, 2015 at 6:37 PM, Gene Cumm wrote:
> > On Sat, Sep 12, 2015 at 10:23 AM, Geert Stappers wrote:
> >> diff --git a/core/fs/pxe/dhcp_option.c b/core/fs/pxe/dhcp_option.c
> >> index 8d93a6a..b82e944 100644
> >> --- a/core/fs/pxe/dhcp_option.c
> >> +++ b/core/fs/pxe/dhcp_option.c
> >> @@ -252,4 +252,6 @@ void parse_dhcp(const void *pkt, size_t
pkt_len, int pkt_type)
> >>
> >>      if (over_load & 2)
> >>          parse_dhcp_options(dhcp->sname, 64, 0);
> >> +
> >> +    /* What about option 66, tftserver_name ?   FIXME */
> >>  }
> >
> > Something like this would be preferable except it's not quite so
> > simple.  We'd need to not store BOOTP siaddr before parsing. 
Store a
> > pointer to the string during parsing if serverip is unset.  After all
> > parsing, if the pointer is set, attempt to resolve then set serverip.
> > Last, if serverip is not set, copy siaddr to serverip.
> 
> Perhaps a more important question is if ANY PXE implementation uses
> DHCP option 66 over BOOTP field siaddr.
Quoting the spec ( I used
http://www.pix.net/software/pxeboot/archive/pxespec.pdf )

  sname, 64 bytes, Can be overloaded if using Opt 66

Hope this helps


Groeten
Geert Stappers
-- 
Leven en laten leven

On Sun, Sep 13, 2015 at 3:46 PM, Geert Stappers via Syslinux
<syslinux at zytor.com> wrote:
> On Sat, Sep 12, 2015 at 06:56:04PM -0400, Gene Cumm via Syslinux wrote:
>> On Sat, Sep 12, 2015 at 6:37 PM, Gene Cumm wrote:
>> > On Sat, Sep 12, 2015 at 10:23 AM, Geert Stappers wrote:
>> >> diff --git a/core/fs/pxe/dhcp_option.c
b/core/fs/pxe/dhcp_option.c
>> >> index 8d93a6a..b82e944 100644
>> >> --- a/core/fs/pxe/dhcp_option.c
>> >> +++ b/core/fs/pxe/dhcp_option.c
>> >> @@ -252,4 +252,6 @@ void parse_dhcp(const void *pkt, size_t
pkt_len, int pkt_type)
>> >>
>> >>      if (over_load & 2)
>> >>          parse_dhcp_options(dhcp->sname, 64, 0);
>> >> +
>> >> +    /* What about option 66, tftserver_name ?   FIXME */
>> >>  }
>> >
>> > Something like this would be preferable except it's not quite
so
>> > simple.  We'd need to not store BOOTP siaddr before parsing. 
Store a
>> > pointer to the string during parsing if serverip is unset.  After
all
>> > parsing, if the pointer is set, attempt to resolve then set
serverip.
>> > Last, if serverip is not set, copy siaddr to serverip.
>>
>> Perhaps a more important question is if ANY PXE implementation uses
>> DHCP option 66 over BOOTP field siaddr.
>
> Quoting the spec ( I used
http://www.pix.net/software/pxeboot/archive/pxespec.pdf )
>
>   sname, 64 bytes, Can be overloaded if using Opt 66
>
> Hope this helps
I didn't question the specification, where BOOT field sname or DHCP
option 66 could be loaded with some string.  I questioned if any
_implementation_ (ie a PC with PXE OROM) bothers to pay attention to
sname/66 before BOOTP field siaddr or if a DHCP daemon would set
siaddr to 0 while setting sname/66.

If the BOOTP/DHCP specifications require that siaddr be set to the
first possible value of sname/66 (which I can't seem to verify with
the RFCs), then using siaddr/sname would only serve for fall back if
DNS is easier to redirect than DHCP to reconfigure.

-- 
-Gene