X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?a=blobdiff_plain;f=src%2Flibsystemd%2Fsd-rtnl%2Frtnl-message.c;h=096a32236cdb5d4f08a6c2c130f46d8e1b429874;hb=ee3a6a51e5b098aa0c9641ed71d275c459ad2f5a;hp=d55c3673a374ede36297908b030b8b4d2912568d;hpb=01b36069ccddbed35b82dd3b64af3e522ab305fe;p=elogind.git

diff --git a/src/libsystemd/sd-rtnl/rtnl-message.c b/src/libsystemd/sd-rtnl/rtnl-message.c
index d55c3673a..096a32236 100644
--- a/src/libsystemd/sd-rtnl/rtnl-message.c
+++ b/src/libsystemd/sd-rtnl/rtnl-message.c
@@ -24,28 +24,21 @@
 #include <netinet/ether.h>
 #include <stdbool.h>
 #include <unistd.h>
+#include <linux/veth.h>
 
 #include "util.h"
 #include "refcnt.h"
 
 #include "sd-rtnl.h"
+#include "rtnl-util.h"
 #include "rtnl-internal.h"
 
-struct sd_rtnl_message {
-        RefCount n_ref;
-
-        struct nlmsghdr *hdr;
-        size_t container_offset; /* offset from hdr to container start */
-        size_t next_rta_offset; /* offset from hdr to next rta */
-
-        bool sealed:1;
-};
-
-#define CURRENT_CONTAINER(m) ((m)->container_offset ? (struct rtattr*)((uint8_t*)(m)->hdr + (m)->container_offset) : NULL)
+#define GET_CONTAINER(m, i) ((i) < (m)->n_containers ? (struct rtattr*)((uint8_t*)(m)->hdr + (m)->container_offsets[i]) : NULL)
 #define NEXT_RTA(m) ((struct rtattr*)((uint8_t*)(m)->hdr + (m)->next_rta_offset))
 #define UPDATE_RTA(m, new) (m)->next_rta_offset = (uint8_t*)(new) - (uint8_t*)(m)->hdr;
+#define PUSH_CONTAINER(m, new) (m)->container_offsets[(m)->n_containers ++] = (uint8_t*)(new) - (uint8_t*)(m)->hdr;
 
-static int message_new(sd_rtnl_message **ret, size_t initial_size) {
+int message_new(sd_rtnl_message **ret, size_t initial_size) {
         sd_rtnl_message *m;
 
         assert_return(ret, -EINVAL);
@@ -71,77 +64,30 @@ static int message_new(sd_rtnl_message **ret, size_t initial_size) {
         return 0;
 }
 
-int message_new_synthetic_error(int error, uint32_t serial, sd_rtnl_message **ret) {
-        struct nlmsgerr *err;
-        int r;
-
-        assert(error <= 0);
-
-        r = message_new(ret, NLMSG_SPACE(sizeof(struct nlmsgerr)));
-        if (r < 0)
-                return r;
-
-        (*ret)->hdr->nlmsg_len = NLMSG_LENGTH(sizeof(struct nlmsgerr));
-        (*ret)->hdr->nlmsg_type = NLMSG_ERROR;
-        (*ret)->hdr->nlmsg_seq = serial;
-
-        err = NLMSG_DATA((*ret)->hdr);
-
-        err->error = error;
-
-        return 0;
-}
-
-bool message_type_is_route(uint16_t type) {
-        switch (type) {
-                case RTM_NEWROUTE:
-                case RTM_GETROUTE:
-                case RTM_DELROUTE:
-                        return true;
-                default:
-                        return false;
-        }
-}
-
-bool message_type_is_link(uint16_t type) {
-        switch (type) {
-                case RTM_NEWLINK:
-                case RTM_SETLINK:
-                case RTM_GETLINK:
-                case RTM_DELLINK:
-                        return true;
-                default:
-                        return false;
-        }
-}
-
-bool message_type_is_addr(uint16_t type) {
-        switch (type) {
-                case RTM_NEWADDR:
-                case RTM_GETADDR:
-                case RTM_DELADDR:
-                        return true;
-                default:
-                        return false;
-        }
-}
-
 int sd_rtnl_message_route_set_dst_prefixlen(sd_rtnl_message *m, unsigned char prefixlen) {
         struct rtmsg *rtm;
 
+        assert_return(m, -EINVAL);
+        assert_return(m->hdr, -EINVAL);
+        assert_return(rtnl_message_type_is_route(m->hdr->nlmsg_type), -EINVAL);
+
         rtm = NLMSG_DATA(m->hdr);
 
+        if ((rtm->rtm_family == AF_INET && prefixlen > 32) ||
+            (rtm->rtm_family == AF_INET6 && prefixlen > 128))
+                return -ERANGE;
+
         rtm->rtm_dst_len = prefixlen;
 
         return 0;
 }
 
-int sd_rtnl_message_route_new(uint16_t nlmsg_type, unsigned char rtm_family,
+int sd_rtnl_message_new_route(uint16_t nlmsg_type, unsigned char rtm_family,
                               sd_rtnl_message **ret) {
         struct rtmsg *rtm;
         int r;
 
-        assert_return(message_type_is_route(nlmsg_type), -EINVAL);
+        assert_return(rtnl_message_type_is_route(nlmsg_type), -EINVAL);
         assert_return(rtm_family == AF_INET || rtm_family == AF_INET6, -EINVAL);
         assert_return(ret, -EINVAL);
 
@@ -170,13 +116,15 @@ int sd_rtnl_message_route_new(uint16_t nlmsg_type, unsigned char rtm_family,
 int sd_rtnl_message_link_set_flags(sd_rtnl_message *m, unsigned flags, unsigned change) {
         struct ifinfomsg *ifi;
 
+        assert_return(m, -EINVAL);
+        assert_return(m->hdr, -EINVAL);
+        assert_return(rtnl_message_type_is_link(m->hdr->nlmsg_type), -EINVAL);
+        assert_return(change, -EINVAL);
+
         ifi = NLMSG_DATA(m->hdr);
 
         ifi->ifi_flags = flags;
-        if (change)
-                ifi->ifi_change = change;
-        else
-                ifi->ifi_change = 0xffffffff;
+        ifi->ifi_change = change;
 
         return 0;
 }
@@ -184,6 +132,10 @@ int sd_rtnl_message_link_set_flags(sd_rtnl_message *m, unsigned flags, unsigned
 int sd_rtnl_message_link_set_type(sd_rtnl_message *m, unsigned type) {
         struct ifinfomsg *ifi;
 
+        assert_return(m, -EINVAL);
+        assert_return(m->hdr, -EINVAL);
+        assert_return(rtnl_message_type_is_link(m->hdr->nlmsg_type), -EINVAL);
+
         ifi = NLMSG_DATA(m->hdr);
 
         ifi->ifi_type = type;
@@ -191,11 +143,11 @@ int sd_rtnl_message_link_set_type(sd_rtnl_message *m, unsigned type) {
         return 0;
 }
 
-int sd_rtnl_message_link_new(uint16_t nlmsg_type, int index, sd_rtnl_message **ret) {
+int sd_rtnl_message_new_link(uint16_t nlmsg_type, int index, sd_rtnl_message **ret) {
         struct ifinfomsg *ifi;
         int r;
 
-        assert_return(message_type_is_link(nlmsg_type), -EINVAL);
+        assert_return(rtnl_message_type_is_link(nlmsg_type), -EINVAL);
         assert_return(nlmsg_type == RTM_NEWLINK || index > 0, -EINVAL);
         assert_return(ret, -EINVAL);
 
@@ -218,12 +170,60 @@ int sd_rtnl_message_link_new(uint16_t nlmsg_type, int index, sd_rtnl_message **r
         return 0;
 }
 
-int sd_rtnl_message_addr_new(uint16_t nlmsg_type, int index, unsigned char family, unsigned char prefixlen, unsigned char flags, unsigned char scope, sd_rtnl_message **ret) {
+int sd_rtnl_message_addr_set_prefixlen(sd_rtnl_message *m, unsigned char prefixlen) {
+        struct ifaddrmsg *ifa;
+
+        assert_return(m, -EINVAL);
+        assert_return(m->hdr, -EINVAL);
+        assert_return(rtnl_message_type_is_addr(m->hdr->nlmsg_type), -EINVAL);
+
+        ifa = NLMSG_DATA(m->hdr);
+
+        if ((ifa->ifa_family == AF_INET && prefixlen > 32) ||
+            (ifa->ifa_family == AF_INET6 && prefixlen > 128))
+                return -ERANGE;
+
+        ifa->ifa_prefixlen = prefixlen;
+
+        return 0;
+}
+
+int sd_rtnl_message_addr_set_flags(sd_rtnl_message *m, unsigned char flags) {
+        struct ifaddrmsg *ifa;
+
+        assert_return(m, -EINVAL);
+        assert_return(m->hdr, -EINVAL);
+        assert_return(rtnl_message_type_is_addr(m->hdr->nlmsg_type), -EINVAL);
+
+        ifa = NLMSG_DATA(m->hdr);
+
+        ifa->ifa_flags = flags;
+
+        return 0;
+}
+
+int sd_rtnl_message_addr_set_scope(sd_rtnl_message *m, unsigned char scope) {
+        struct ifaddrmsg *ifa;
+
+        assert_return(m, -EINVAL);
+        assert_return(m->hdr, -EINVAL);
+        assert_return(rtnl_message_type_is_addr(m->hdr->nlmsg_type), -EINVAL);
+
+        ifa = NLMSG_DATA(m->hdr);
+
+        ifa->ifa_scope = scope;
+
+        return 0;
+}
+
+int sd_rtnl_message_new_addr(uint16_t nlmsg_type, int index, unsigned char family,
+                             sd_rtnl_message **ret) {
         struct ifaddrmsg *ifa;
         int r;
 
-        assert_return(message_type_is_addr(nlmsg_type), -EINVAL);
+        assert_return(rtnl_message_type_is_addr(nlmsg_type), -EINVAL);
         assert_return(index > 0, -EINVAL);
+        assert_return(family == AF_INET || family == AF_INET6, -EINVAL);
         assert_return(ret, -EINVAL);
 
         r = message_new(ret, NLMSG_SPACE(sizeof(struct ifaddrmsg)));
@@ -235,11 +235,12 @@ int sd_rtnl_message_addr_new(uint16_t nlmsg_type, int index, unsigned char famil
 
         ifa = NLMSG_DATA((*ret)->hdr);
 
-        ifa->ifa_family = family;
-        ifa->ifa_prefixlen = prefixlen;
-        ifa->ifa_flags = flags;
-        ifa->ifa_scope = scope;
         ifa->ifa_index = index;
+        ifa->ifa_family = family;
+        if (family == AF_INET)
+                ifa->ifa_prefixlen = 32;
+        else if (family == AF_INET6)
+                ifa->ifa_prefixlen = 128;
 
         UPDATE_RTA(*ret, IFA_RTA(ifa));
 
@@ -276,7 +277,7 @@ int sd_rtnl_message_link_get_ifindex(sd_rtnl_message *m, int *ifindex) {
 
         assert_return(m, -EINVAL);
         assert_return(m->hdr, -EINVAL);
-        assert_return(message_type_is_link(m->hdr->nlmsg_type), -EINVAL);
+        assert_return(rtnl_message_type_is_link(m->hdr->nlmsg_type), -EINVAL);
         assert_return(ifindex, -EINVAL);
 
         ifi = NLMSG_DATA(m->hdr);
@@ -291,7 +292,7 @@ int sd_rtnl_message_link_get_flags(sd_rtnl_message *m, unsigned *flags) {
 
         assert_return(m, -EINVAL);
         assert_return(m->hdr, -EINVAL);
-        assert_return(message_type_is_link(m->hdr->nlmsg_type), -EINVAL);
+        assert_return(rtnl_message_type_is_link(m->hdr->nlmsg_type), -EINVAL);
         assert_return(flags, -EINVAL);
 
         ifi = NLMSG_DATA(m->hdr);
@@ -308,11 +309,14 @@ static int add_rtattr(sd_rtnl_message *m, unsigned short type, const void *data,
         struct nlmsghdr *new_hdr;
         struct rtattr *rta;
         char *padding;
+        unsigned i;
 
         assert(m);
         assert(m->hdr);
+        assert(!m->sealed);
         assert(NLMSG_ALIGN(m->hdr->nlmsg_len) == m->hdr->nlmsg_len);
         assert(!data || data_length > 0);
+        assert(data || m->n_containers < RTNL_CONTAINER_DEPTH);
 
         /* get the size of the new rta attribute (with padding at the end) */
         rta_length = RTA_LENGTH(data_length);
@@ -329,16 +333,16 @@ static int add_rtattr(sd_rtnl_message *m, unsigned short type, const void *data,
         /* get pointer to the attribute we are about to add */
         rta = (struct rtattr *) ((uint8_t *) m->hdr + m->hdr->nlmsg_len);
 
-        /* if we are inside a container, extend it */
-        if (CURRENT_CONTAINER(m))
-                CURRENT_CONTAINER(m)->rta_len += message_length - m->hdr->nlmsg_len;
+        /* if we are inside containers, extend them */
+        for (i = 0; i < m->n_containers; i++)
+                GET_CONTAINER(m, i)->rta_len += message_length - m->hdr->nlmsg_len;
 
         /* fill in the attribute */
         rta->rta_type = type;
         rta->rta_len = rta_length;
         if (!data) {
                 /* this is the start of a new container */
-                m->container_offset = m->hdr->nlmsg_len;
+                m->container_offsets[m->n_containers ++] = m->hdr->nlmsg_len;
         } else {
                 /* we don't deal with the case where the user lies about the type
                  * and gives us too little data (so don't do that)
@@ -360,6 +364,7 @@ int sd_rtnl_message_append_string(sd_rtnl_message *m, unsigned short type, const
         int r;
 
         assert_return(m, -EINVAL);
+        assert_return(!m->sealed, -EPERM);
         assert_return(data, -EINVAL);
 
         r = sd_rtnl_message_get_type(m, &rtm_type);
@@ -372,8 +377,8 @@ int sd_rtnl_message_append_string(sd_rtnl_message *m, unsigned short type, const
                 case RTM_SETLINK:
                 case RTM_GETLINK:
                 case RTM_DELLINK:
-                        if (CURRENT_CONTAINER(m)) {
-                                if (CURRENT_CONTAINER(m)->rta_type != IFLA_LINKINFO ||
+                        if (m->n_containers == 1) {
+                                if (GET_CONTAINER(m, 0)->rta_type != IFLA_LINKINFO ||
                                     type != IFLA_INFO_KIND)
                                         return -ENOTSUP;
                         } else {
@@ -404,28 +409,68 @@ int sd_rtnl_message_append_string(sd_rtnl_message *m, unsigned short type, const
         return 0;
 }
 
-int sd_rtnl_message_append_u16(sd_rtnl_message *m, unsigned short type, uint16_t data) {
+int sd_rtnl_message_append_u8(sd_rtnl_message *m, unsigned short type, uint8_t data) {
         uint16_t rtm_type;
         int r;
 
         assert_return(m, -EINVAL);
+        assert_return(!m->sealed, -EPERM);
 
         r = sd_rtnl_message_get_type(m, &rtm_type);
         if (r < 0)
                 return r;
 
-        /* check that the type is correct */
         switch (rtm_type) {
                 case RTM_NEWLINK:
                 case RTM_SETLINK:
                 case RTM_GETLINK:
                 case RTM_DELLINK:
                         switch (type) {
-                                case IFLA_VLAN_ID:
-                                        break;
-                                default:
-                                        return -ENOTSUP;
+                                case IFLA_CARRIER:
+                                case IFLA_OPERSTATE:
+                                case IFLA_LINKMODE:
+                                break;
+                        default:
+                                return -ENOTSUP;
                         }
+
+                        break;
+                default:
+                        return -ENOTSUP;
+        }
+
+        r = add_rtattr(m, type, &data, sizeof(uint8_t));
+        if (r < 0)
+                return r;
+
+        return 0;
+}
+
+
+int sd_rtnl_message_append_u16(sd_rtnl_message *m, unsigned short type, uint16_t data) {
+        uint16_t rtm_type;
+        int r;
+
+        assert_return(m, -EINVAL);
+        assert_return(!m->sealed, -EPERM);
+
+        r = sd_rtnl_message_get_type(m, &rtm_type);
+        if (r < 0)
+                return r;
+
+        /* check that the type is correct */
+        switch (rtm_type) {
+                case RTM_NEWLINK:
+                case RTM_SETLINK:
+                case RTM_GETLINK:
+                case RTM_DELLINK:
+                        if (m->n_containers == 2 &&
+                            GET_CONTAINER(m, 0)->rta_type == IFLA_LINKINFO &&
+                            GET_CONTAINER(m, 1)->rta_type == IFLA_INFO_DATA &&
+                            type == IFLA_VLAN_ID)
+                                break;
+                        else
+                                return -ENOTSUP;
                         break;
                 default:
                         return -ENOTSUP;
@@ -443,6 +488,7 @@ int sd_rtnl_message_append_u32(sd_rtnl_message *m, unsigned short type, uint32_t
         int r;
 
         assert_return(m, -EINVAL);
+        assert_return(!m->sealed, -EPERM);
 
         r = sd_rtnl_message_get_type(m, &rtm_type);
         if (r < 0)
@@ -458,6 +504,14 @@ int sd_rtnl_message_append_u32(sd_rtnl_message *m, unsigned short type, uint32_t
                                 case IFLA_MASTER:
                                 case IFLA_MTU:
                                 case IFLA_LINK:
+                                case IFLA_GROUP:
+                                case IFLA_TXQLEN:
+                                case IFLA_WEIGHT:
+                                case IFLA_NET_NS_FD:
+                                case IFLA_NET_NS_PID:
+                                case IFLA_PROMISCUITY:
+                                case IFLA_NUM_TX_QUEUES:
+                                case IFLA_NUM_RX_QUEUES:
                                         break;
                                 default:
                                         return -ENOTSUP;
@@ -471,6 +525,7 @@ int sd_rtnl_message_append_u32(sd_rtnl_message *m, unsigned short type, uint32_t
                                 case RTA_PRIORITY:
                                 case RTA_IIF:
                                 case RTA_OIF:
+                                case RTA_MARK:
                                         break;
                                 default:
                                         return -ENOTSUP;
@@ -494,6 +549,7 @@ int sd_rtnl_message_append_in_addr(sd_rtnl_message *m, unsigned short type, cons
         int r;
 
         assert_return(m, -EINVAL);
+        assert_return(!m->sealed, -EPERM);
         assert_return(data, -EINVAL);
 
         r = sd_rtnl_message_get_type(m, &rtm_type);
@@ -555,6 +611,7 @@ int sd_rtnl_message_append_in6_addr(sd_rtnl_message *m, unsigned short type, con
         int r;
 
         assert_return(m, -EINVAL);
+        assert_return(!m->sealed, -EPERM);
         assert_return(data, -EINVAL);
 
         r = sd_rtnl_message_get_type(m, &rtm_type);
@@ -613,6 +670,7 @@ int sd_rtnl_message_append_ether_addr(sd_rtnl_message *m, unsigned short type, c
         int r;
 
         assert_return(m, -EINVAL);
+        assert_return(!m->sealed, -EPERM);
         assert_return(data, -EINVAL);
 
         sd_rtnl_message_get_type(m, &rtm_type);
@@ -645,26 +703,31 @@ int sd_rtnl_message_open_container(sd_rtnl_message *m, unsigned short type) {
         uint16_t rtm_type;
 
         assert_return(m, -EINVAL);
-        assert_return(!CURRENT_CONTAINER(m), -EINVAL);
+        assert_return(!m->sealed, -EPERM);
 
         sd_rtnl_message_get_type(m, &rtm_type);
 
-        if (message_type_is_link(rtm_type)) {
-                if (type == IFLA_LINKINFO)
+        if (rtnl_message_type_is_link(rtm_type)) {
+
+                if ((type == IFLA_LINKINFO && m->n_containers == 0) ||
+                    (type == IFLA_INFO_DATA && m->n_containers == 1 &&
+                     GET_CONTAINER(m, 0)->rta_type == IFLA_LINKINFO))
                         return add_rtattr(m, type, NULL, 0);
-                else
-                        return -ENOTSUP;
-        } else
-                return -ENOTSUP;
+                else if (type == VETH_INFO_PEER && m->n_containers == 2 &&
+                         GET_CONTAINER(m, 1)->rta_type == IFLA_INFO_DATA &&
+                         GET_CONTAINER(m, 0)->rta_type == IFLA_LINKINFO)
+                        return add_rtattr(m, type, NULL, sizeof(struct ifinfomsg));
+        }
 
-        return 0;
+        return -ENOTSUP;
 }
 
 int sd_rtnl_message_close_container(sd_rtnl_message *m) {
         assert_return(m, -EINVAL);
-        assert_return(CURRENT_CONTAINER(m), -EINVAL);
+        assert_return(!m->sealed, -EPERM);
+        assert_return(m->n_containers > 0, -EINVAL);
 
-        m->container_offset = 0;
+        m->n_containers --;
 
         return 0;
 }
@@ -674,35 +737,58 @@ int sd_rtnl_message_read(sd_rtnl_message *m, unsigned short *type, void **data)
         uint16_t rtm_type;
         int r;
 
-        assert(m);
-        assert(m->next_rta_offset);
-        assert(type);
-        assert(data);
+        assert_return(m, -EINVAL);
+        assert_return(m->sealed, -EPERM);
+        assert_return(m->next_rta_offset, -EINVAL);
+        assert_return(type, -EINVAL);
+        assert_return(data, -EINVAL);
 
-        remaining_size = m->hdr->nlmsg_len - m->next_rta_offset;
+        /* only read until the end of the current container */
+        if (m->n_containers)
+                remaining_size = GET_CONTAINER(m, m->n_containers - 1)->rta_len -
+                                 (m->next_rta_offset -
+                                  m->container_offsets[m->n_containers - 1]);
+        else
+                remaining_size = m->hdr->nlmsg_len - m->next_rta_offset;
 
         if (!RTA_OK(NEXT_RTA(m), remaining_size))
                 return 0;
 
-        /* make sure we don't try to read a container
-         * TODO: add support for entering containers for reading */
+        /* if we read a container, enter it and return its type */
         r = sd_rtnl_message_get_type(m, &rtm_type);
         if (r < 0)
                 return r;
 
-        if (message_type_is_link(rtm_type) &&
-            NEXT_RTA(m)->rta_type == IFLA_LINKINFO)
-               return -EINVAL;
-
-        *data = RTA_DATA(NEXT_RTA(m));
         *type = NEXT_RTA(m)->rta_type;
 
-        UPDATE_RTA(m, RTA_NEXT(NEXT_RTA(m), remaining_size));
+        if (rtnl_message_type_is_link(rtm_type) &&
+            ((m->n_containers == 0 &&
+              NEXT_RTA(m)->rta_type == IFLA_LINKINFO) ||
+             (m->n_containers == 1 &&
+              GET_CONTAINER(m, 0)->rta_type == IFLA_LINKINFO &&
+              NEXT_RTA(m)->rta_type == IFLA_INFO_DATA))) {
+                *data = NULL;
+                PUSH_CONTAINER(m, NEXT_RTA(m));
+                UPDATE_RTA(m, RTA_DATA(NEXT_RTA(m)));
+        } else {
+                *data = RTA_DATA(NEXT_RTA(m));
+                UPDATE_RTA(m, RTA_NEXT(NEXT_RTA(m), remaining_size));
+        }
 
         return 1;
 }
 
-uint32_t message_get_serial(sd_rtnl_message *m) {
+int sd_rtnl_message_exit_container(sd_rtnl_message *m) {
+        assert_return(m, -EINVAL);
+        assert_return(m->sealed, -EINVAL);
+        assert_return(m->n_containers > 0, -EINVAL);
+
+        m->n_containers --;
+
+        return 0;
+}
+
+uint32_t rtnl_message_get_serial(sd_rtnl_message *m) {
         assert(m);
         assert(m->hdr);
 
@@ -723,17 +809,24 @@ int sd_rtnl_message_get_errno(sd_rtnl_message *m) {
         return err->error;
 }
 
-int message_seal(sd_rtnl *nl, sd_rtnl_message *m) {
-        assert(nl);
+int rtnl_message_seal(sd_rtnl *nl, sd_rtnl_message *m) {
+        int r;
+
         assert(m);
         assert(m->hdr);
 
         if (m->sealed)
                 return -EPERM;
 
-        m->hdr->nlmsg_seq = nl->serial++;
+        if (nl)
+                m->hdr->nlmsg_seq = nl->serial++;
+
         m->sealed = true;
 
+        r = sd_rtnl_message_rewind(m);
+        if (r < 0)
+                return r;
+
         return 0;
 }
 
@@ -806,6 +899,9 @@ int socket_read_message(sd_rtnl *nl, sd_rtnl_message **ret) {
         if (r < 0)
                 return r;
 
+        /* don't allow sealing/appending to received messages */
+        m->sealed = true;
+
         addr_len = sizeof(addr);
 
         k = recvfrom(nl->fd, m->hdr, need,
@@ -891,6 +987,7 @@ int sd_rtnl_message_rewind(sd_rtnl_message *m) {
         struct rtmsg *rtm;
 
         assert_return(m, -EINVAL);
+        assert_return(m->sealed, -EPERM);
         assert_return(m->hdr, -EINVAL);
 
         switch(m->hdr->nlmsg_type) {
@@ -920,5 +1017,7 @@ int sd_rtnl_message_rewind(sd_rtnl_message *m) {
                         return -ENOTSUP;
         }
 
+        m->n_containers = 0;
+
         return 0;
 }