kernel-netlink: Use dynamic buffer if Netlink message doesn't fit static buffer

diff --git a/src/libcharon/plugins/kernel_netlink/kernel_netlink_shared.c b/src/libcharon/plugins/kernel_netlink/kernel_netlink_shared.c
index f3b5b1d4abf0e36e370d9c4d52f755100e732f9f..82835f59d3c022b2f6b6d88e6dd2e2b379e37f92 100644 (file)
--- a/src/libcharon/plugins/kernel_netlink/kernel_netlink_shared.c
+++ b/src/libcharon/plugins/kernel_netlink/kernel_netlink_shared.c
@@ -1,8 +1,8 @@
 /*
  * Copyright (C) 2014 Martin Willi
  * Copyright (C) 2014 revosec AG
- * Copyright (C) 2008 Tobias Brunner
- * Hochschule fuer Technik Rapperswil
+ * Copyright (C) 2008-2017 Tobias Brunner
+ * HSR Hochschule fuer Technik Rapperswil
  *
  * This program is free software; you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the
@@ -44,6 +44,7 @@
 #include <linux/xfrm.h>
 #include <errno.h>
 #include <unistd.h>
+#include <sys/ioctl.h>
 
 #include "kernel_netlink_shared.h"
 
@@ -189,7 +190,7 @@ static bool write_msg(private_netlink_socket_t *this, struct nlmsghdr *msg)
  * Read a single Netlink message from socket, return 0 on error, -1 on timeout
  */
 static ssize_t read_msg(private_netlink_socket_t *this,
-                                               char *buf, size_t buflen, bool block)
+                                               char **buf, size_t buflen, bool block)
 {
        ssize_t len;
 
@@ -208,12 +209,21 @@ static ssize_t read_msg(private_netlink_socket_t *this,
                        return -1;
                }
        }
-       len = recv(this->socket, buf, buflen, MSG_TRUNC|(block ? 0 : MSG_DONTWAIT));
-       if (len > buflen)
+       len = recv(this->socket, NULL, 0, MSG_TRUNC|MSG_PEEK|(block?0:MSG_DONTWAIT));
+       if (len < 0)
        {
-               DBG1(DBG_KNL, "netlink response exceeds buffer size");
+               DBG1(DBG_KNL, "failed to determine netlink response size: %s",
+                        strerror(errno));
                return 0;
        }
+       else if (len > buflen)
+       {
+               DBG2(DBG_KNL, "netlink response (%d bytes) exceeds buffer size "
+                        "(%zu bytes), allocating dynamic buffer", len, buflen);
+               buflen = len;
+               *buf = malloc(buflen);
+       }
+       len = recv(this->socket, *buf, buflen, block ? 0 : MSG_DONTWAIT);
        if (len < 0)
        {
                if (errno != EAGAIN && errno != EWOULDBLOCK && errno != EINTR)
@@ -264,11 +274,11 @@ static bool queue(private_netlink_socket_t *this, struct nlmsghdr *buf)
 static bool read_and_queue(private_netlink_socket_t *this, bool block)
 {
        struct nlmsghdr *hdr;
-       char buf[this->buflen];
+       char static_buf[this->buflen], *buf = static_buf;
        ssize_t len, read_len;
        bool wipe = FALSE;
 
-       len = read_len = read_msg(this, buf, sizeof(buf), block);
+       len = read_len = read_msg(this, &buf, this->buflen, block);
        if (len == -1)
        {
                return TRUE;
@@ -294,6 +304,10 @@ static bool read_and_queue(private_netlink_socket_t *this, bool block)
        {
                memwipe(buf, read_len);
        }
+       if (buf != static_buf)
+       {
+               free(buf);
+       }
        return FALSE;
 }