[PATCH net-next iproute2 1/2 v2] libnetlink: Add test for error code returned from netlink reply

[Cyrill Gorcunov <gorcunov@gmail.com>]

In case if some diag module is not present in the system,
say the kernel is not modern enough, we simply skip the
error code reported. Instead we should check for data
length in NLMSG_DONE and process unsupported case.

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
---
 lib/libnetlink.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index 2279935..232daee 100644
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -312,6 +312,22 @@ int rtnl_dump_filter_l(struct rtnl_handle *rth,
 					dump_intr = 1;
 
 				if (h->nlmsg_type == NLMSG_DONE) {
+					if (rth->proto == NETLINK_SOCK_DIAG) {
+						if (h->nlmsg_len < NLMSG_LENGTH(sizeof(int))) {
+							fprintf(stderr, "DONE truncated\n");
+							return -1;
+						} else {
+							int len = *(int *)NLMSG_DATA(h);
+							if (len < 0) {
+								errno = -len;
+								if (errno == ENOENT ||
+								    errno == EOPNOTSUPP)
+									return -1;
+								perror("RTNETLINK answers");
+								return len;
+							}
+						}
+					}
 					found_done = 1;
 					break; /* process next filter */
 				}
-- 
2.7.4