Fix copyfile() not preserving source mode with restrictive umask

copyfile() passes the source mode to open(2), which applies the umask,
so a 0644 file copied with umask 0027 ends up 0640.

Apply the source mode with fchmod() after creating the destination.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

ChangeLog.md

@@ -8,6 +8,8 @@ All notable changes to the project are documented in this file.
 --------------
 
 ### Fixes
+- Fix `copyfile()` not preserving the source file mode when the process
+  umask is more restrictive
 - Fix `mkpath()`, and `fmkpath()`, not applying the given mode when the
   process umask is more restrictive, e.g., requesting 0755 with umask
   0027 silently created a 0750 directory

src/copyfile.c

@@ -208,12 +208,20 @@ ssize_t copyfile(const char *src, const char *dst, int len, int opt)
 		goto exit;
 	}
 
+	/* open(2) applies umask, we want the source file mode */
+	if (fchmod(out, st.st_mode & 07777)) {
+		saved_errno = errno;
+		size = -1;
+		goto close_exit;
+	}
+
 	size = do_copy(in, out, num, buffer, BUFSIZ);
 	if (size < 0)
 		saved_errno = errno;
 	else if (keep_mtim)
 		set_mtime(in, out);
 
+close_exit:
 	close(out);
 	close(in);
 

test/copyfile.c

@@ -123,9 +123,32 @@ static int _copyfile()
 	return rc;
 }
 
+/* copyfile() must preserve source mode, even with a restrictive umask */
+static int _mode(void)
+{
+	const char *src = "/tmp/libite-mode-src", *dst = "/tmp/libite-mode-dst";
+	struct stat st;
+	mode_t old;
+	int rc = 1;
+
+	if (touch(src) || chmod(src, 0644))
+		return test(1, "copyfile() mode, prepare %s", src);
+
+	old = umask(0077);
+	if (copyfile(src, dst, 0, 0) >= 0 && !stat(dst, &st))
+		rc = (st.st_mode & 07777) != 0644;
+	umask(old);
+
+	erase(src);
+	erase(dst);
+
+	return test(rc, "copyfile() preserves mode 0644 with umask 0077");
+}
+
 int main(void)
 {
 	return	_fcopyfile() ||
 		_copyfile()  ||
-		_sz();
+		_sz()        ||
+		_mode();
 }