lib: return error if an incomplete message was read

If recvmsg indicates that the message read was truncated libnl retries
to read the complete message after increasing the message buffer. This
only works if the message flags MSG_PEEK | MSG_TRUNC are set. If
NL_MSG_PEEK is not enabled on the nl_sock structure, flags are left
empty and the rest of the truncated message is discarded, hence a
subsequent recvmsg returns the next message (in case of a multipart
message, the NLMSG_DONE) is read and returned.
This patch aborts message processing if the message was truncated and
the NL_MSG_PEEK flags was not activated for the nl_sock structure.

http://lists.infradead.org/pipermail/libnl/2015-June/001888.html

[thaller@redhat.com: add NL_CAPABILITY_NL_RECV_FAIL_TRUNK_NO_PEEK]

Signed-off-by: Thomas Egerer <hakke_007@gmx.de>
Signed-off-by: Thomas Haller <thaller@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/lib/nl.c b/lib/nl.c
index 8fc9ec10..f06e9a0a 100644
--- a/lib/nl.c
+++ b/lib/nl.c
@@ -725,6 +725,13 @@ retry:
 
 	if (iov.iov_len < n || (msg.msg_flags & MSG_TRUNC)) {
 		void *tmp;
+
+		/* respond with error to an incomplete message */
+		if (!(sk->s_flags & NL_MSG_PEEK)) {
+			retval = -NLE_MSG_TRUNC;
+			goto abort;
+		}
+
 		/* Provided buffer is not long enough, enlarge it
 		 * to size of n (which should be total length of the message)
 		 * and try again. */