um: Use race-free temporary file creation

Open the memory mapped file with the O_TMPFILE flag when available.

Signed-off-by: Mickaël Salaün <mic@digikod.net>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Richard Weinberger <richard@nod.at>
Acked-by: Tristan Schmelcher <tschmelcher@google.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

diff --git a/arch/um/os-Linux/mem.c b/arch/um/os-Linux/mem.c
index 840d573..8b17676 100644 (file)
--- a/arch/um/os-Linux/mem.c
+++ b/arch/um/os-Linux/mem.c
@@ -106,6 +106,17 @@ static int __init make_tempfile(const char *template)
                }
        }
 
+#ifdef O_TMPFILE
+       fd = open(tempdir, O_CLOEXEC | O_RDWR | O_EXCL | O_TMPFILE, 0700);
+       /*
+        * If the running system does not support O_TMPFILE flag then retry
+        * without it.
+        */
+       if (fd != -1 || (errno != EINVAL && errno != EISDIR &&
+                       errno != EOPNOTSUPP))
+               return fd;
+#endif
+
        tempname = malloc(strlen(tempdir) + strlen(template) + 1);
        if (tempname == NULL)
                return -1;