netlink: fix reception of large netlink messages

If received netlink message is bigger than the buffer provided by the
application, netlink message flag will contain the MSG_TRUNC flag. In
this case it is up to the application to allocate a buffer large enough
to receive the full message and to call recv() again.

diff --git a/src/daemon/netlink.c b/src/daemon/netlink.c
index c0d1dcf1fcd5001de1d00684c46f2da2c168bfd3..c8da30eb7e20acc7a7412a287edd19eff5d8ae8d 100644 (file)
--- a/src/daemon/netlink.c
+++ b/src/daemon/netlink.c
@@ -360,8 +360,9 @@ netlink_recv(int s,
     struct interfaces_device_list *ifs,
     struct interfaces_address_list *ifas)
 {
-       char reply[NETLINK_BUFFER] __attribute__ ((aligned));
-       int end = 0;
+       int end = 0, ret = 0;
+       int flags = MSG_PEEK | MSG_TRUNC;
+       struct iovec iov;
        int link_update = 0;
 
        struct interfaces_device *ifdold;
@@ -370,13 +371,16 @@ netlink_recv(int s,
        struct interfaces_address *ifanew;
        char addr[INET6_ADDRSTRLEN + 1];
 
+       iov.iov_len = NETLINK_BUFFER;
+       iov.iov_base = malloc(iov.iov_len);
+       if (!iov.iov_base) {
+               log_warn("netlink", "not enough memory");
+               return -1;
+       }
+
        while (!end) {
                ssize_t len;
                struct nlmsghdr *msg;
-               struct iovec iov = {
-                       .iov_base = reply,
-                       .iov_len = NETLINK_BUFFER
-               };
                struct sockaddr_nl peer = { .nl_family = AF_NETLINK };
                struct msghdr rtnl_reply = {
                        .msg_iov = &iov,
@@ -385,17 +389,49 @@ netlink_recv(int s,
                        .msg_namelen = sizeof(struct sockaddr_nl)
                };
 
-               len = recvmsg(s, &rtnl_reply, 0);
+retry:
+               len = recvmsg(s, &rtnl_reply, flags);
                if (len == -1) {
                        if (errno == EAGAIN || errno == EWOULDBLOCK) {
                                log_debug("netlink", "should have received something, but didn't");
-                               return 0;
+                               ret = 0;
+                               goto out;
                        }
                        log_warnx("netlink", "unable to receive netlink answer");
-                       return -1;
+                       ret = -1;
+                       goto out;
                }
-               if (!len) return 0;
-               for (msg = (struct nlmsghdr*)(void*)reply;
+               if (!len) {
+                       ret = 0;
+                       goto out;
+               }
+
+               if (iov.iov_len < len || (rtnl_reply.msg_flags & MSG_TRUNC)) {
+                       void *tmp;
+
+                       /* Provided buffer is not large enough, enlarge it
+                        * to size of len (which should be total length of the message)
+                        * and try again. */
+                       iov.iov_len = len;
+                       tmp = realloc(iov.iov_base, iov.iov_len);
+                       if (!tmp) {
+                               log_warn("netlink", "not enough memory");
+                               ret = -1;
+                               goto out;
+                       }
+                       log_debug("netlink", "enlarge message size to %zu bytes", len);
+                       iov.iov_base = tmp;
+                       flags = 0;
+                       goto retry;
+               }
+
+               if (flags != 0) {
+                       /* Buffer is big enough, do the actual reading */
+                       flags = 0;
+                       goto retry;
+               }
+
+               for (msg = (struct nlmsghdr*)(void*)(iov.iov_base);
                     NLMSG_OK(msg, len);
                     msg = NLMSG_NEXT(msg, len)) {
                        if (!(msg->nlmsg_flags & NLM_F_MULTI))
@@ -507,6 +543,7 @@ netlink_recv(int s,
                                    msg->nlmsg_type, msg->nlmsg_len);
                        }
                }
+               flags = MSG_PEEK | MSG_TRUNC;
        }
 end:
        if (link_update) {
@@ -549,7 +586,10 @@ end:
                        }
                }
        }
-       return 0;
+
+out:
+       free(iov.iov_base);
+       return ret;
 }
 
 static int