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.
 (backport from rev. 43501)

diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index a65fb4b162ea15c5e4a3898bdf9bfe5a2a76fec2..b4cab361ff786eae4ae3b4c1cdd79442ae957717 100644 (file)
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -5458,9 +5458,20 @@ 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();