Allow for zero byte iovec with MSG_PEEK | MSG_TRUNC in recvmsg.

This allows for peeking at the length of the next message on a netlink socket
without pulling it off the socket's buffer/queue, allowing tools like 'ip' to
work.

This CL also fixes an issue where dump_done_errno was not included in the
NLMSG_DONE messages payload.

Issue #769

PiperOrigin-RevId: 274068637

1 files changed, 7 insertions, 0 deletions

diff --git a/test/syscalls/linux/socket_netlink_util.cc b/test/syscalls/linux/socket_netlink_util.cc
index 36b6560c2..fcb8f8a88 100644
--- a/test/syscalls/linux/socket_netlink_util.cc
+++ b/test/syscalls/linux/socket_netlink_util.cc
@@ -91,6 +91,13 @@ PosixError NetlinkRequestResponse(
          NLMSG_OK(hdr, len); hdr = NLMSG_NEXT(hdr, len)) {
       fn(hdr);
       type = hdr->nlmsg_type;
+      // Done should include an integer payload for dump_done_errno.
+      // See net/netlink/af_netlink.c:netlink_dump
+      // Some tools like the 'ip' tool check the minimum length of the
+      // NLMSG_DONE message.
+      if (type == NLMSG_DONE) {
+        EXPECT_GE(hdr->nlmsg_len, NLMSG_LENGTH(sizeof(int)));
+      }
     }
   } while (type != NLMSG_DONE && type != NLMSG_ERROR);