From 47eae6ce0c28b1984f8f5ec4c2f7bc428cf3b6ad Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Fri, 17 Apr 2020 22:26:14 +0200
Subject: [PATCH] socket-util: add recvmsg_safe() wrapper that handles
 MSG_CTRUNC

---
 src/basic/socket-util.c | 21 +++++++++++++++++++++
 src/basic/socket-util.h |  2 ++
 2 files changed, 23 insertions(+)

diff --git a/src/basic/socket-util.c b/src/basic/socket-util.c
index ad467ab8511..2d0564e66f0 100644
--- a/src/basic/socket-util.c
+++ b/src/basic/socket-util.c
@@ -1171,3 +1171,24 @@ int socket_bind_to_ifindex(int fd, int ifindex) {
 
         return socket_bind_to_ifname(fd, ifname);
 }
+
+ssize_t recvmsg_safe(int sockfd, struct msghdr *msg, int flags) {
+        ssize_t n;
+
+        /* A wrapper around recvmsg() that checks for MSG_CTRUNC, and turns it into an error, in a reasonably
+         * safe way, closing any SCM_RIGHTS fds in the error path.
+         *
+         * Note that unlike our usual coding style this might modify *msg on failure. */
+
+        n = recvmsg(sockfd, msg, flags);
+        if (n < 0)
+                return -errno;
+
+        if (FLAGS_SET(msg->msg_flags, MSG_CTRUNC)) {
+                cmsg_close_all(msg);
+                return -EXFULL; /* a recognizable error code */
+        }
+
+        return n;
+
+}
diff --git a/src/basic/socket-util.h b/src/basic/socket-util.h
index 24e12139516..95643135df7 100644
--- a/src/basic/socket-util.h
+++ b/src/basic/socket-util.h
@@ -199,3 +199,5 @@ static inline int setsockopt_int(int fd, int level, int optname, int value) {
 
 int socket_bind_to_ifname(int fd, const char *ifname);
 int socket_bind_to_ifindex(int fd, int ifindex);
+
+ssize_t recvmsg_safe(int sockfd, struct msghdr *msg, int flags);
-- 
2.39.2