bug #1461855: make os.fdopen() add the O_APPEND flag if using "a" mode.

glibc, for example, does this already on its own, but it seems that
the solaris libc doesn't. This leads to Python code being able to over-
write file contents even though having specified "a" mode.

diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index abf69a98dead40dab021797cc691a428df8ea774..631833f77a771758aea3a969800fce5212068960 100644 (file)
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -5768,9 +5768,20 @@ posix_fdopen(PyObject *self, PyObject *args)
                             "invalid file mode '%s'", mode);
                return NULL;
        }
-
        Py_BEGIN_ALLOW_THREADS
-       fp = fdopen(fd, mode);
+       if (mode[0] == 'a') {
+               /* try to make sure the O_APPEND flag is set */
+               int flags;
+               flags = fcntl(fd, F_GETFL);
+               if (flags != -1)
+                       fcntl(fd, F_SETFL, flags | O_APPEND);
+               fp = fdopen(fd, mode);
+               if (fp == NULL)
+                       /* restore old mode if fdopen failed */
+                       fcntl(fd, F_SETFL, flags);
+       } else {
+               fp = fdopen(fd, mode);
+       }
        Py_END_ALLOW_THREADS
        if (fp == NULL)
                return posix_error();