2016-03-17 1:06 GMT+08:00 Jeff King [off-list ref]:

On Wed, Mar 16, 2016 at 06:07:43PM +0800, Hui Yiqun wrote:

quoted

+     if (runtime_dir && *runtime_dir)
+             git_runtime_dir = mkpathdup("%s/git/", runtime_dir);
+     else
+             git_runtime_dir = mkpathdup("/tmp/git-%d", uid);

Here we allocate the string, but later we may return NULL on error,
leaking the allocated memory.

Yes, do you think goto is a good solution for clearup?

quoted

+     if (!lstat(git_runtime_dir, &st)) {
+             /*
+              * As described in XDG base dir spec[1], the subdirectory
+              * under $XDG_RUNTIME_DIR or its fallback MUST be owned by
+              * the user, and its unix access mode MUST be 0700.
+              *
+              * Calling chmod or chown silently may cause security
+              * problem if somebody chdir to it, sleep, and then, try
+              * to open our protected runtime cache or socket.
+              * So we just put warning and left it to user to solve.
+              *
+              * [1]https://specifications.freedesktop.org/basedir-spec/
+              * basedir-spec-latest.html
+              */

OK. I think these checks should be sufficient to deal with the /tmp race
I mentioned elsewhere in the thread (assuming that an attacker cannot
flip the uid back and forth in the same way, but that should be true on
Unix systems).

quoted

+             if ((st.st_mode & 0777) != S_IRWXU) {
+                     fprintf(stderr,
+                                     "permission of runtime directory '%s' "
+                                     "MUST be 0700 instead of 0%o\n",
+                                     git_runtime_dir, (st.st_mode & 0777));
+                     return NULL;
+             } else if (st.st_uid != uid) {
+                     fprintf(stderr,
+                                     "owner of runtime directory '%s' "
+                                     "MUST be %d instead of %d\n",
+                                     git_runtime_dir, uid, st.st_uid);
+                     return NULL;
+             }

Should these be using warning(), rather than a raw fprintf?

Well, I will replace it.

During the greping. I found that I should also wrap my warning strings
with _() for i18n.

quoted

+     } else {
+             if (safe_create_leading_directories_const(git_runtime_dir) < 0) {
+                     fprintf(stderr,
+                                     "unable to create directories for '%s'\n",
+                                     git_runtime_dir);
+                     return NULL;
+             }
+             if (mkdir(git_runtime_dir, 0700) < 0) {
+                     fprintf(stderr,
+                                     "unable to mkdir '%s'\n", git_runtime_dir);
+                     return NULL;
+             }
+     }

And this retains the un-racy mkdir(). Good.

quoted

+     free(git_runtime_dir);
+     return mkpathdup("%s/%s", git_runtime_dir, filename);

This mkpathdup accesses the string we just freed?

It might be easier to just use a strbuf here, and then you can append to
it at the end.

I think so. Thanks.

-Peff