mingw: short-circuit the conversion of `/dev/null` to UTF-16

In the next commit, we want to disallow accessing any path that contains
any segment that is equivalent to `NUL`. In particular, we want to
disallow accessing `NUL` (e.g. to prevent any repository from being
checked out that contains a file called `NUL`, as that is not a valid
file name on Windows).

However, there are legitimate use cases within Git itself to write to
the Null device. As Git is really a Linux project, it does not abstract
that idea, though, but instead uses `/dev/null` to describe this
intention.

So let's side-step the validation _specifically_ in the case that we
want to write to (or read from) `/dev/null`, via a dedicated short-cut
in the code that skips the call to `validate_win32_path()`.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/compat/mingw.c b/compat/mingw.c
index bd24d913f93f3cc077eb0d7545dfebf2491a4aac..03c4538ec886aebb8e5c25c370f25aa64e0c637b 100644 (file)
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -484,16 +484,16 @@ int mingw_open (const char *filename, int oflags, ...)
                return -1;
        }
 
-       if (filename && !strcmp(filename, "/dev/null"))
-               filename = "nul";
-
        if ((oflags & O_APPEND) && !is_local_named_pipe_path(filename))
                open_fn = mingw_open_append;
        else
                open_fn = _wopen;
 
-       if (xutftowcs_path(wfilename, filename) < 0)
+       if (filename && !strcmp(filename, "/dev/null"))
+               wcscpy(wfilename, L"nul");
+       else if (xutftowcs_path(wfilename, filename) < 0)
                return -1;
+
        fd = open_fn(wfilename, oflags, mode);
 
        if (fd < 0 && (oflags & O_ACCMODE) != O_RDONLY && errno == EACCES) {
@@ -556,10 +556,13 @@ FILE *mingw_fopen (const char *filename, const char *otype)
                return NULL;
        }
        if (filename && !strcmp(filename, "/dev/null"))
-               filename = "nul";
-       if (xutftowcs_path(wfilename, filename) < 0 ||
-               xutftowcs(wotype, otype, ARRAY_SIZE(wotype)) < 0)
+               wcscpy(wfilename, L"nul");
+       else if (xutftowcs_path(wfilename, filename) < 0)
                return NULL;
+
+       if (xutftowcs(wotype, otype, ARRAY_SIZE(wotype)) < 0)
+               return NULL;
+
        if (hide && !access(filename, F_OK) && set_hidden_flag(wfilename, 0)) {
                error("could not unhide %s", filename);
                return NULL;
@@ -583,10 +586,13 @@ FILE *mingw_freopen (const char *filename, const char *otype, FILE *stream)
                return NULL;
        }
        if (filename && !strcmp(filename, "/dev/null"))
-               filename = "nul";
-       if (xutftowcs_path(wfilename, filename) < 0 ||
-               xutftowcs(wotype, otype, ARRAY_SIZE(wotype)) < 0)
+               wcscpy(wfilename, L"nul");
+       else if (xutftowcs_path(wfilename, filename) < 0)
                return NULL;
+
+       if (xutftowcs(wotype, otype, ARRAY_SIZE(wotype)) < 0)
+               return NULL;
+
        if (hide && !access(filename, F_OK) && set_hidden_flag(wfilename, 0)) {
                error("could not unhide %s", filename);
                return NULL;