Work out the size of the buffer we need to read netlink messages as recent

64-bit Linux kernels have increased their header size and overflowed
the fixed buffer we used.

Could also fix #192.

diff --git a/if-linux.c b/if-linux.c
index ab1bbe6e9f8cd8a7d6be59ff59211be8a2940ff2..4a06259d1a7bb842bdad359daa53365d1083fb52 100644 (file)
--- a/if-linux.c
+++ b/if-linux.c
@@ -54,8 +54,6 @@
 #include "dhcp.h"
 #include "net.h"
 
-#define BUFFERLEN 256
-
 static int sock_fd;
 static struct sockaddr_nl sock_nl;
 
@@ -144,14 +142,38 @@ static int
 get_netlink(int fd, int flags,
     int (*callback)(struct nlmsghdr *))
 {
-       char *buffer = NULL;
-       ssize_t bytes;
+       char *buf = NULL, *nbuf;
+       ssize_t buflen = 0, bytes;
        struct nlmsghdr *nlm;
        int r = -1;
 
-       buffer = xzalloc(sizeof(char) * BUFFERLEN);
        for (;;) {
-               bytes = recv(fd, buffer, BUFFERLEN, flags);
+               bytes = recv(fd, NULL, 0,
+                   flags | MSG_PEEK | MSG_DONTWAIT | MSG_TRUNC);
+               if (bytes == -1) {
+                       if (errno == EAGAIN) {
+                               r = 0;
+                               goto eexit;
+                       }
+                       if (errno == EINTR)
+                               continue;
+                       goto eexit;
+               } else if (bytes == buflen) {
+                       /* Support kernels older than 2.6.22 */
+                       if (bytes == 0)
+                               bytes = 512;
+                       else
+                               bytes *= 2;
+               }
+               if (buflen < bytes) {
+                       /* Alloc 1 more so we work with older kernels */
+                       buflen = bytes + 1;
+                       nbuf = realloc(buf, buflen);
+                       if (nbuf == NULL)
+                               goto eexit;
+                       buf = nbuf;
+               }
+               bytes = recv(fd, buf, buflen, flags);
                if (bytes == -1) {
                        if (errno == EAGAIN) {
                                r = 0;
@@ -161,7 +183,7 @@ get_netlink(int fd, int flags,
                                continue;
                        goto eexit;
                }
-               for (nlm = (struct nlmsghdr *)buffer;
+               for (nlm = (struct nlmsghdr *)buf;
                     NLMSG_OK(nlm, (size_t)bytes);
                     nlm = NLMSG_NEXT(nlm, bytes))
                {
@@ -172,7 +194,7 @@ get_netlink(int fd, int flags,
        }
 
 eexit:
-       free(buffer);
+       free(buf);
        return r;
 }