<linux/mptcp.h> conflict with <netinet/in.h> in C library

[ossama-othman]

Including <linux/mptcp.h> before the C library <netinet/in.h> header causes symbol redefinition errors at compile-time due to duplicate declarations and definitions in the <linux/in.h> header included by <linux/mptcp.h>.

The following simple code may be used to reproduce the compile-time errors:

// foo.c
#include <linux/mptcp.h>
#include <netinet/in.h>

$ gcc -fsyntax-only foo.c 
In file included from foo.c:2:
/usr/include/netinet/in.h:31:8: error: redefinition of ‘struct in_addr’
   31 | struct in_addr
      |        ^~~~~~~
In file included from /usr/include/linux/mptcp.h:7,
                 from foo.c:1:
/usr/include/linux/in.h:89:8: note: originally defined here
   89 | struct in_addr {
      |        ^~~~~~~
...

[ossama-othman]

The following patch addresses the problem by forcing <netinet/in.h> to be included before <linux/in.h> so that the C library compatibility in <linux/libc-compat.h> is enabled when including <linux/mptcp.h> in user space code:

diff --git a/include/uapi/linux/mptcp.h b/include/uapi/linux/mptcp.h
index 921963589904..dfe19bf13f4c 100644
--- a/include/uapi/linux/mptcp.h
+++ b/include/uapi/linux/mptcp.h
@@ -2,16 +2,17 @@
 #ifndef _UAPI_MPTCP_H
 #define _UAPI_MPTCP_H
 
+#ifndef __KERNEL__
+#include <netinet/in.h>                /* for sockaddr_in and sockaddr_in6     */
+#include <sys/socket.h>                /* for struct sockaddr                  */
+#endif
+
 #include <linux/const.h>
 #include <linux/types.h>
 #include <linux/in.h>          /* for sockaddr_in                      */
 #include <linux/in6.h>         /* for sockaddr_in6                     */
 #include <linux/socket.h>      /* for sockaddr_storage and sa_family   */
 
-#ifndef __KERNEL__
-#include <sys/socket.h>                /* for struct sockaddr                  */
-#endif
-
 #define MPTCP_SUBFLOW_FLAG_MCAP_REM            _BITUL(0)
 #define MPTCP_SUBFLOW_FLAG_MCAP_LOC            _BITUL(1)
 #define MPTCP_SUBFLOW_FLAG_JOIN_REM            _BITUL(2)

[matttbe]

The patch has been applied in our tree (and sent to net-next)

• 334cee2: mptcp: fix conflict with <netinet/in.h>
• Results: c1baa3a..bbf8496 (export)