From b27f791691b149ea660618dd93e7b9792d4e7680 Mon Sep 17 00:00:00 2001
From: Mike Yuan <me@yhndnzj.com>
Date: Sun, 26 Jan 2025 01:32:42 +0100
Subject: [PATCH] terminal-util: stop doing 0/upper bound check in tty_is_vc()

tty_is_vc() is more often than not used for simple "categorization"
than validity check. E.g. in logind, we first recognize the tty
"looks like vc", and then use vtnr_from_tty() where range check
is performed and vtnr is extracted. In such cases, we want to reject
invalid vtnr from clients rather than silently carry on, hence
let's remove bound check in tty_is_vc().

Fixes #36166
Replaces #36167 and #36175
---
 src/basic/terminal-util.c | 39 +++++++++++++++++++++++++--------------
 1 file changed, 25 insertions(+), 14 deletions(-)

diff --git a/src/basic/terminal-util.c b/src/basic/terminal-util.c
index eeeb6576239..2baf2830b17 100644
--- a/src/basic/terminal-util.c
+++ b/src/basic/terminal-util.c
@@ -764,31 +764,25 @@ int make_console_stdio(void) {
         return 0;
 }
 
-bool tty_is_vc(const char *tty) {
+static int vtnr_from_tty_raw(const char *tty, unsigned *ret) {
         assert(tty);
 
-        return vtnr_from_tty(tty) >= 0;
-}
+        tty = skip_dev_prefix(tty);
 
-bool tty_is_console(const char *tty) {
-        assert(tty);
+        const char *e = startswith(tty, "tty");
+        if (!e)
+                return -EINVAL;
 
-        return streq(skip_dev_prefix(tty), "console");
+        return safe_atou(e, ret);
 }
 
 int vtnr_from_tty(const char *tty) {
+        unsigned u;
         int r;
 
         assert(tty);
 
-        tty = skip_dev_prefix(tty);
-
-        const char *e = startswith(tty, "tty");
-        if (!e)
-                return -EINVAL;
-
-        unsigned u;
-        r = safe_atou(e, &u);
+        r = vtnr_from_tty_raw(tty, &u);
         if (r < 0)
                 return r;
         if (!vtnr_is_valid(u))
@@ -797,6 +791,23 @@ int vtnr_from_tty(const char *tty) {
         return (int) u;
 }
 
+bool tty_is_vc(const char *tty) {
+        assert(tty);
+
+        /* NB: for >= 0 values no range check is conducted here, on the assumption that the caller will
+         * either extract vtnr through vtnr_from_tty() later where ERANGE would be reported, or doesn't care
+         * about whether it's strictly valid, but only asking "does this fall into the vt catogory?", for which
+         * "yes" seems to be a better answer. */
+
+        return vtnr_from_tty_raw(tty, /* ret = */ NULL) >= 0;
+}
+
+bool tty_is_console(const char *tty) {
+        assert(tty);
+
+        return streq(skip_dev_prefix(tty), "console");
+}
+
 int resolve_dev_console(char **ret) {
         int r;
 
-- 
2.47.3