[PATCH v2 1/3] net: Get pxe config file from dhcp option 209

[Sean Edmond]

On 2023-10-23 10:54 p.m., Heinrich Schuchardt wrote:
> On 10/24/23 02:21, seanedmond at linux.microsoft.com wrote:
>> From: Sean Edmond <seanedmond at microsoft.com>
>>
>> Allow dhcp server pass pxe config file full path by using option 209
>>
>> Signed-off-by: Sean Edmond <seanedmond at microsoft.com>
>> ---
>>   cmd/Kconfig |  4 ++++
>>   cmd/pxe.c   | 10 ++++++++++
>>   net/bootp.c | 21 +++++++++++++++++++++
>>   3 files changed, 35 insertions(+)
>>
>> diff --git a/cmd/Kconfig b/cmd/Kconfig
>> index 5bc0a92d57..adbb1a6187 100644
>> --- a/cmd/Kconfig
>> +++ b/cmd/Kconfig
>> @@ -1826,6 +1826,10 @@ config BOOTP_PXE_CLIENTARCH
>>       default 0x15 if ARM
>>       default 0x0 if X86
>>
>> +config BOOTP_PXE_DHCP_OPTION
>> +    bool "Request & store 'pxe_configfile' from BOOTP/DHCP server"
>> +    depends on BOOTP_PXE
>
> Why should this be disabled by default?
>
> Do we really want a separate config variable?
>
I expect most won't use this option to get the file path (they'll use 
the default paths as per the PXE specification).  It makes more sense 
for me to keep it optional, like many of the other options?
>> +
>>   config BOOTP_VCI_STRING
>>       string
>>       depends on CMD_BOOTP
>> diff --git a/cmd/pxe.c b/cmd/pxe.c
>> index 704589702f..9404f44518 100644
>> --- a/cmd/pxe.c
>> +++ b/cmd/pxe.c
>> @@ -65,6 +65,8 @@ static int pxe_dhcp_option_path(struct pxe_context 
>> *ctx, unsigned long pxefile_a
>>       int ret = get_pxe_file(ctx, pxelinux_configfile, pxefile_addr_r);
>>
>>       free(pxelinux_configfile);
>> +    /* set to NULL to avoid double-free if DHCP is tried again */
>> +    pxelinux_configfile = NULL;
>>
>>       return ret;
>>   }
>> @@ -141,6 +143,14 @@ int pxe_get(ulong pxefile_addr_r, char 
>> **bootdirp, ulong *sizep, bool use_ipv6)
>>                 env_get("bootfile"), use_ipv6))
>>           return -ENOMEM;
>>
>> +    if (IS_ENABLED(CONFIG_BOOTP_PXE_DHCP_OPTION) &&
>> +        pxelinux_configfile && !use_ipv6) {
>> +        if (pxe_dhcp_option_path(&ctx, pxefile_addr_r) > 0)
>> +            goto done;
>> +
>> +        goto error_exit;
>> +    }
>> +
>>       if (IS_ENABLED(CONFIG_DHCP6_PXE_DHCP_OPTION) &&
>>           pxelinux_configfile && use_ipv6) {
>>           if (pxe_dhcp_option_path(&ctx, pxefile_addr_r) > 0)
>> diff --git a/net/bootp.c b/net/bootp.c
>> index 7b0f45e18a..6800290963 100644
>> --- a/net/bootp.c
>> +++ b/net/bootp.c
>> @@ -26,6 +26,7 @@
>>   #ifdef CONFIG_BOOTP_RANDOM_DELAY
>>   #include "net_rand.h"
>>   #endif
>> +#include <malloc.h>
>>
>>   #define BOOTP_VENDOR_MAGIC    0x63825363    /* RFC1048 Magic Cookie */
>>
>> @@ -601,6 +602,10 @@ static int dhcp_extended(u8 *e, int 
>> message_type, struct in_addr server_ip,
>>       *e++  = 42;
>>       *cnt += 1;
>>   #endif
>> +    if (IS_ENABLED(CONFIG_BOOTP_PXE_DHCP_OPTION)) {
>> +        *e++ = 209;    /* PXELINUX Config File */
>> +        *cnt += 1;
>> +    }
>>       /* no options, so back up to avoid sending an empty request 
>> list */
>>       if (*cnt == 0)
>>           e -= 2;
>> @@ -909,6 +914,22 @@ static void dhcp_process_options(uchar *popt, 
>> uchar *end)
>>                   net_boot_file_name[size] = 0;
>>               }
>>               break;
>> +        case 209:    /* PXELINUX Config File */
>
> This 209 appears in multiple places. Please, define a constant, e.g.
> DHCP_OPTION_CONFIG_FILE, in bootp.h and use the symbolic name. Please,
> document the constant referring to RFC 5071.
fixed in v3.
>
>> +            if (IS_ENABLED(CONFIG_BOOTP_PXE_DHCP_OPTION)) {
>> +                /* In case it has already been allocated when get 
>> DHCP Offer packet,
>> +                 * free first to avoid memory leak.
>> +                 */
>> +                if (pxelinux_configfile)
>> +                    free(pxelinux_configfile);
>> +
>> +                pxelinux_configfile = (char *)malloc((oplen + 1) * 
>> sizeof(char));
>> +
>> +                if (pxelinux_configfile)
>> +                    strlcpy(pxelinux_configfile, popt + 2, oplen + 1);
>> +                else
>> +                    printf("Error: Failed to allocate 
>> pxelinux_configfile\n");
>
> We do the same in dhcp6_parse_options(). Please, factor out a common
> function to avoid code duplication.
I would prefer to keep these seperate for several reasons:
- our DHCP server team has asked for the DHCP6 "pxe config file" parsing 
to change.  I attempted to add to upstream here: 
https://lore.kernel.org/u-boot/20230725231329.5653-1-seanedmond@linux.microsoft.com/. 
I will attempt to submitted that patch again
- PXE config file isn't standardized yet for DHCPv6 (the current 
implementation was a proposal from our DHCP server team)
- LWIP will eventually superceed bootp.c in u-boot, but we'll probably 
be keeping dhcpv6.c for a bit (keeping the duplicate code will make the 
migration easier)
>
> Best regards
>
> Heinrich
>
>> +            }
>> +            break;
>>           default:
>>   #if defined(CONFIG_BOOTP_VENDOREX)
>>               if (dhcp_vendorex_proc(popt))