libnet: Add support for DHCPv4 options 209 and 210

There are two dedicated DHCP options for loading PXELINUX config files,
option 209 (config file name) and 210 (path prefix). We should support
them, too, in case some users want to configure their boot flow this way.
See RFC 5071 and the following URL for more details:
https://www.syslinux.org/wiki/index.php?title=PXELINUX#DHCP_options

Unlike most other strings in libnet, I've chosen to not use fixed-size
arrays for these two strings, but to allocate the memory via malloc here.
We always have to make sure not to overflow the stack in Paflof, so
adding 2 * 256 byte arrays to struct filename_ip sounded just too
dangerous to me.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

1 files changed, 33 insertions, 0 deletions

diff --git a/lib/libnet/dhcp.c b/lib/libnet/dhcp.c
index d3e5170..85cd7c0 100644
--- a/lib/libnet/dhcp.c
+++ b/lib/libnet/dhcp.c
@@ -79,6 +79,8 @@
 #define DHCP_TFTP_SERVER      66
 #define DHCP_BOOTFILE         67
 #define DHCP_CLIENT_ARCH      93
+#define DHCP_PXELINUX_CFGFILE 209   /* See RFC 5071 */
+#define DHCP_PXELINUX_PREFIX  210
 #define DHCP_ENDOPT         0xFF
 #define DHCP_PADOPT         0x00
 
@@ -167,6 +169,8 @@ static uint32_t dhcp_siaddr_ip     = 0;
 static char   dhcp_filename[256];
 static char   dhcp_tftp_name[256];
 static uint32_t dhcp_xid;
+static char *pxelinux_cfgfile;
+static char *pxelinux_prefix;
 
 static char   * response_buffer;
 
@@ -185,6 +189,8 @@ int32_t dhcpv4(char *ret_buffer, filename_ip_t *fn_ip)
 	strcpy(dhcp_filename, "");
 	strcpy(dhcp_tftp_name, "");
 
+	pxelinux_cfgfile = pxelinux_prefix = NULL;
+
 	response_buffer = ret_buffer;
 
 	if (dhcp_attempt(fd) == 0)
@@ -232,6 +238,10 @@ int32_t dhcpv4(char *ret_buffer, filename_ip_t *fn_ip)
 	fn_ip -> server_ip = dhcp_tftp_ip;
 	strcpy(fn_ip->filename, dhcp_filename);
 
+	fn_ip->pl_cfgfile = pxelinux_cfgfile;
+	fn_ip->pl_prefix = pxelinux_prefix;
+	pxelinux_cfgfile = pxelinux_prefix = NULL;
+
 	return 0;
 }
 
@@ -456,6 +466,26 @@ static int32_t dhcp_decode_options(uint8_t opt_field[], uint32_t opt_len,
 			offset += 4;
 			break;
 
+		case DHCP_PXELINUX_CFGFILE:
+			pxelinux_cfgfile = malloc(opt_field[offset + 1] + 1);
+			if (pxelinux_cfgfile) {
+				memcpy(pxelinux_cfgfile, opt_field + offset + 2,
+				       opt_field[offset + 1]);
+				pxelinux_cfgfile[opt_field[offset + 1]] = 0;
+			}
+			offset += 2 + opt_field[offset + 1];
+			break;
+
+		case DHCP_PXELINUX_PREFIX:
+			pxelinux_prefix = malloc(opt_field[offset + 1] + 1);
+			if (pxelinux_prefix) {
+				memcpy(pxelinux_prefix, opt_field + offset + 2,
+				       opt_field[offset + 1]);
+				pxelinux_prefix[opt_field[offset + 1]] = 0;
+			}
+			offset += 2 + opt_field[offset + 1];
+			break;
+
 		case DHCP_PADOPT :
 			offset++;
 			break;
@@ -681,6 +711,9 @@ static void dhcp_send_request(int fd)
 	opt.request_list[DHCP_ROUTER] = 1;
 	opt.request_list[DHCP_TFTP_SERVER] = 1;
 	opt.request_list[DHCP_BOOTFILE] = 1;
+	opt.request_list[DHCP_PXELINUX_CFGFILE] = 1;
+	opt.request_list[DHCP_PXELINUX_PREFIX] = 1;
+
 	opt.request_list[DHCP_CLIENT_ARCH] = USE_DHCPARCH;
 	opt.flag[DHCP_CLIENT_ARCH] = USE_DHCPARCH;