[PATCH for-4.19 2/3] tools/libxs: Fix CLOEXEC handling in get_socket()

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

get_socket() opens a socket, then uses fcntl() to set CLOEXEC.  This is racy
with exec().

Open the socket with SOCK_CLOEXEC.  Use the same compatibility strategy as
O_CLOEXEC on ancient versions of Linux.

Reported-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Anthony PERARD <anthony@xxxxxxxxxxxxxx>
CC: Juergen Gross <jgross@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
CC: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
 tools/libs/store/xs.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/tools/libs/store/xs.c b/tools/libs/store/xs.c
index 037e79d98b58..11a766c50887 100644
--- a/tools/libs/store/xs.c
+++ b/tools/libs/store/xs.c
@@ -44,6 +44,10 @@
 #define O_CLOEXEC 0
 #endif
 
+#ifndef SOCK_CLOEXEC
+#define SOCK_CLOEXEC 0
+#endif
+
 struct xs_stored_msg {
        XEN_TAILQ_ENTRY(struct xs_stored_msg) list;
        struct xsd_sockmsg hdr;
@@ -207,16 +211,14 @@ int xs_fileno(struct xs_handle *h)
 static int get_socket(const char *connect_to)
 {
        struct sockaddr_un addr;
-       int sock, saved_errno, flags;
+       int sock, saved_errno;
 
-       sock = socket(PF_UNIX, SOCK_STREAM, 0);
+       sock = socket(PF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0);
        if (sock < 0)
                return -1;
 
-       if ((flags = fcntl(sock, F_GETFD)) < 0)
-               goto error;
-       flags |= FD_CLOEXEC;
-       if (fcntl(sock, F_SETFD, flags) < 0)
+       /* Compat for non-SOCK_CLOEXEC environments.  Racy. */
+       if (!SOCK_CLOEXEC && !set_cloexec(sock))
                goto error;
 
        addr.sun_family = AF_UNIX;
-- 
2.39.2