From de14a376ffbd08b00732ef491cb7cc15b6ab3416 Mon Sep 17 00:00:00 2001
From: Thomas Haller <thaller@redhat.com>
Date: Tue, 9 Feb 2021 18:10:12 +0100
Subject: [PATCH] dhcp/nettools: refactor parsing of DHCP lease (mtu)

---
 src/core/dhcp/nm-dhcp-nettools.c | 54 +++++++++-----------------------
 src/core/dhcp/nm-dhcp-utils.c    | 32 +++++++++++++++++++
 src/core/dhcp/nm-dhcp-utils.h    |  5 +++
 3 files changed, 51 insertions(+), 40 deletions(-)

diff --git a/src/core/dhcp/nm-dhcp-nettools.c b/src/core/dhcp/nm-dhcp-nettools.c
index ae1aeadfa4..14b788e38d 100644
--- a/src/core/dhcp/nm-dhcp-nettools.c
+++ b/src/core/dhcp/nm-dhcp-nettools.c
@@ -326,27 +326,6 @@ lease_get_in_addr(NDhcp4ClientLease *lease, guint8 option, struct in_addr *addrp
     return TRUE;
 }
 
-static gboolean
-lease_get_u16(NDhcp4ClientLease *lease, uint8_t option, uint16_t *u16p)
-{
-    uint8_t *data;
-    size_t   n_data;
-    uint16_t be16;
-    int      r;
-
-    r = n_dhcp4_client_lease_query(lease, option, &data, &n_data);
-    if (r)
-        return FALSE;
-
-    if (n_data != sizeof(be16))
-        return FALSE;
-
-    memcpy(&be16, data, sizeof(be16));
-
-    *u16p = ntohs(be16);
-    return TRUE;
-}
-
 static gboolean
 lease_parse_address(NDhcp4ClientLease *lease,
                     NMIP4Config *      ip4_config,
@@ -710,24 +689,6 @@ lease_parse_routes(NDhcp4ClientLease *lease,
     }
 }
 
-static void
-lease_parse_mtu(NDhcp4ClientLease *lease, NMIP4Config *ip4_config, GHashTable *options)
-{
-    uint16_t mtu;
-
-    if (!lease_get_u16(lease, NM_DHCP_OPTION_DHCP4_INTERFACE_MTU, &mtu))
-        return;
-
-    if (mtu < 68)
-        return;
-
-    nm_dhcp_option_add_option_u64(options,
-                                  _nm_dhcp_option_dhcp4_options,
-                                  NM_DHCP_OPTION_DHCP4_INTERFACE_MTU,
-                                  mtu);
-    nm_ip4_config_set_mtu(ip4_config, mtu, NM_IP_CONFIG_SOURCE_DHCP);
-}
-
 static void
 lease_parse_metered(NDhcp4ClientLease *lease, NMIP4Config *ip4_config, GHashTable *options)
 {
@@ -997,6 +958,10 @@ lease_to_ip4_config(NMDedupMultiIndex *multi_idx,
 {
     gs_unref_object NMIP4Config *ip4_config = NULL;
     gs_unref_hashtable GHashTable *options  = NULL;
+    guint8 *                       l_data;
+    gsize                          l_data_len;
+    guint16                        v_u16;
+    int                            r;
 
     g_return_val_if_fail(lease != NULL, NULL);
 
@@ -1012,7 +977,16 @@ lease_to_ip4_config(NMDedupMultiIndex *multi_idx,
     lease_parse_address_list(lease, ip4_config, NM_DHCP_OPTION_DHCP4_DOMAIN_NAME_SERVER, options);
     lease_parse_domainname(lease, ip4_config, options);
     lease_parse_search_domains(lease, ip4_config, options);
-    lease_parse_mtu(lease, ip4_config, options);
+
+    r = n_dhcp4_client_lease_query(lease, NM_DHCP_OPTION_DHCP4_INTERFACE_MTU, &l_data, &l_data_len);
+    if (r == 0 && nm_dhcp_lease_data_parse_mtu(l_data, l_data_len, &v_u16)) {
+        nm_dhcp_option_add_option_u64(options,
+                                      _nm_dhcp_option_dhcp4_options,
+                                      NM_DHCP_OPTION_DHCP4_INTERFACE_MTU,
+                                      v_u16);
+        nm_ip4_config_set_mtu(ip4_config, v_u16, NM_IP_CONFIG_SOURCE_DHCP);
+    }
+
     lease_parse_metered(lease, ip4_config, options);
 
     lease_parse_hostname(lease, options);
diff --git a/src/core/dhcp/nm-dhcp-utils.c b/src/core/dhcp/nm-dhcp-utils.c
index a6555bce24..bf8d5887e4 100644
--- a/src/core/dhcp/nm-dhcp-utils.c
+++ b/src/core/dhcp/nm-dhcp-utils.c
@@ -9,6 +9,7 @@
 #include <arpa/inet.h>
 
 #include "nm-glib-aux/nm-dedup-multi.h"
+#include "nm-std-aux/unaligned.h"
 
 #include "nm-dhcp-utils.h"
 #include "nm-utils.h"
@@ -834,3 +835,34 @@ nm_dhcp_utils_get_dhcp6_event_id(GHashTable *lease)
 
     return g_strdup_printf("%s|%s", iaid, start);
 }
+
+/*****************************************************************************/
+
+gboolean
+nm_dhcp_lease_data_parse_u16(const guint8 *data, gsize n_data, uint16_t *out_val)
+{
+    if (n_data != 2)
+        return FALSE;
+
+    *out_val = unaligned_read_be16(data);
+    return TRUE;
+}
+
+gboolean
+nm_dhcp_lease_data_parse_mtu(const guint8 *data, gsize n_data, uint16_t *out_val)
+{
+    uint16_t mtu;
+
+    if (!nm_dhcp_lease_data_parse_u16(data, n_data, &mtu))
+        return FALSE;
+
+    if (mtu < 68) {
+        /* https://tools.ietf.org/html/rfc2132#section-5.1:
+         *
+         * The minimum legal value for the MTU is 68. */
+        return FALSE;
+    }
+
+    *out_val = mtu;
+    return TRUE;
+}
diff --git a/src/core/dhcp/nm-dhcp-utils.h b/src/core/dhcp/nm-dhcp-utils.h
index f5bc53a215..52e1ea4fb1 100644
--- a/src/core/dhcp/nm-dhcp-utils.h
+++ b/src/core/dhcp/nm-dhcp-utils.h
@@ -40,4 +40,9 @@ char **nm_dhcp_parse_search_list(guint8 *data, size_t n_data);
 
 char *nm_dhcp_utils_get_dhcp6_event_id(GHashTable *lease);
 
+/*****************************************************************************/
+
+gboolean nm_dhcp_lease_data_parse_u16(const guint8 *data, gsize n_data, guint16 *out_val);
+gboolean nm_dhcp_lease_data_parse_mtu(const guint8 *data, gsize n_data, guint16 *out_val);
+
 #endif /* __NETWORKMANAGER_DHCP_UTILS_H__ */