From 896da834e7126759ef69c33347055c593abedde3 Mon Sep 17 00:00:00 2001 From: Jeremy Kerr Date: Fri, 25 Oct 2013 14:34:30 +0800 Subject: [PATCH 1/1] discover/network: Allow for arbitrary-sized netlink messages Currently, we drop any netlink data beyond our 4096-byte buffer. This means that we can only parse a limited number of network interfaces. This change uses recvmsg with MSG_PEEK to determine the size of an incoming netlink message before doing the actual recvmsg. This way, we can realloc our buffer to suit. Signed-off-by: Jeremy Kerr --- discover/network.c | 46 +++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 41 insertions(+), 5 deletions(-) diff --git a/discover/network.c b/discover/network.c index edb7358..d39f7a7 100644 --- a/discover/network.c +++ b/discover/network.c @@ -25,6 +25,7 @@ #define HWADDR_SIZE 6 #define PIDFILE_BASE (LOCAL_STATE_DIR "/petitboot/") +#define INITIAL_BUFSIZE 4096 #define for_each_nlmsg(buf, nlmsg, len) \ for (nlmsg = (struct nlmsghdr *)buf; \ @@ -58,6 +59,8 @@ struct network { struct device_handler *handler; struct waiter *waiter; int netlink_sd; + void *netlink_buf; + unsigned int netlink_buf_size; bool manual_config; bool dry_run; }; @@ -116,6 +119,10 @@ static int network_init_netlink(struct network *network) return -1; } + network->netlink_buf_size = INITIAL_BUFSIZE; + network->netlink_buf = talloc_array(network, char, + network->netlink_buf_size); + return 0; } @@ -426,19 +433,48 @@ static int network_netlink_process(void *arg) { struct network *network = arg; struct nlmsghdr *nlmsg; + struct msghdr msg; + struct iovec iov; unsigned int len; - char buf[4096]; - int rc; + int rc, flags; + + memset(&msg, 0, sizeof(msg)); + msg.msg_iov = &iov; + msg.msg_iovlen = 1; + + flags = MSG_PEEK; + +retry: + iov.iov_len = network->netlink_buf_size; + iov.iov_base = network->netlink_buf; + + rc = recvmsg(network->netlink_sd, &msg, flags); - rc = recv(network->netlink_sd, buf, sizeof(buf), 0); if (rc < 0) { - perror("netlink recv"); + perror("netlink recv header"); return -1; } len = rc; - for_each_nlmsg(buf, nlmsg, len) + /* if the netlink message was larger than our buffer, realloc + * before reading again */ + if (len > network->netlink_buf_size || msg.msg_flags & MSG_TRUNC) { + network->netlink_buf_size *= 2; + network->netlink_buf = talloc_realloc(network, + network->netlink_buf, + char *, + network->netlink_buf_size); + goto retry; + } + + /* otherwise, we're good to read the entire message without PEEK */ + if (flags == MSG_PEEK) { + flags = 0; + goto retry; + } + + for_each_nlmsg(network->netlink_buf, nlmsg, len) network_handle_nlmsg(network, nlmsg); return 0; -- 2.39.2