sway

commit 31a83bd48d9aad2a039565fc39f1a52bd0cdf17d
parent 0b709702c134fcba2b8210ac6f85b8b2665484d0
Author: Teddy Reed <teddy@casualhacking.io>
Date:   Mon, 10 Feb 2020 21:29:26 -0500

Fix ordering of setgid and setuid

It looks like the code to drop privileges may have been broken via
commit 37f0e1f. That commit reverted the correct order from #911, which
first drops the gid then the uid. If setuid is called first then the
target user may not have the ability to setgid.

Diffstat:
M
sway/main.c
 | 
11
++++++++---

1 file changed, 8 insertions(+), 3 deletions(-)
diff --git a/sway/main.c b/sway/main.c
@@ -186,12 +186,17 @@ static void log_kernel(void) {
 
 static bool drop_permissions(void) {
 	if (getuid() != geteuid() || getgid() != getegid()) {
-		if (setuid(getuid()) != 0 || setgid(getgid()) != 0) {
-			sway_log(SWAY_ERROR, "Unable to drop root, refusing to start");
+		// Set the gid and uid in the correct order.
+		if (setgid(getgid()) != 0) {
+			sway_log(SWAY_ERROR, "Unable to drop root group, refusing to start");
+			return false;
+		}
+		if (setuid(getuid()) != 0) {
+			sway_log(SWAY_ERROR, "Unable to drop root user, refusing to start");
 			return false;
 		}
 	}
-	if (setuid(0) != -1) {
+	if (setgid(0) != -1 || setuid(0) != -1) {
 		sway_log(SWAY_ERROR, "Unable to drop root (we shouldn't be able to "
 			"restore it after setuid), refusing to start");
 		return false;