From 8f61a7d34a33c2ec912c3f4404d69586e721c75a Mon Sep 17 00:00:00 2001
From: rpkak <rpkak@noreply.codeberg.org>
Date: Thu, 17 Sep 2026 08:59:38 +0200
Subject: [PATCH] libzigc: strnlen, wcsnlen: don't read past first zero

Previously is was assumed, that all of str[0..max] is readable.
---
 lib/c/string.zig  | 5 ++++-
 lib/c/wchar.zig   | 7 +++++--
 lib/std/c.zig     | 2 ++
 test/c/string.zig | 9 +++++++++
 test/c/wchar.zig  | 9 +++++++++
 5 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/lib/c/string.zig b/lib/c/string.zig
index 2cd0c0467b46e06370f2e1d7de58a34db7d38584..94b94c65e9a022a4fd626be8ee48882ee7794e7b 100644
--- a/lib/c/string.zig
+++ b/lib/c/string.zig
@@ -224,7 +224,10 @@ fn stpncpy(noalias dst: [*]c_char, noalias src: [*:0]const c_char, max: usize) c
 }
 
 fn strnlen(str: [*:0]const c_char, max: usize) callconv(.c) usize {
-    return std.mem.findScalar(u8, @ptrCast(str[0..max]), 0) orelse max;
+    for (0..max) |i| {
+        if (str[i] == 0) return i;
+    }
+    return max;
 }
 
 fn memmem(haystack: *const anyopaque, haystack_len: usize, needle: *const anyopaque, needle_len: usize) callconv(.c) ?*anyopaque {
diff --git a/lib/c/wchar.zig b/lib/c/wchar.zig
index 24aca6b0c869d4900cd4724160c760a8bcfc98cb..eb9611514141e53665b333308c85aa26054257a7 100644
--- a/lib/c/wchar.zig
+++ b/lib/c/wchar.zig
@@ -79,11 +79,14 @@ fn wmemset(dest: [*]wchar_t, elem: wchar_t, len: usize) callconv(.c) [*]wchar_t
 }
 
 fn wcslen(str: [*:0]const wchar_t) callconv(.c) usize {
-    return wcsnlen(str, std.math.maxInt(usize));
+    return std.mem.len(str);
 }
 
 fn wcsnlen(str: [*:0]const wchar_t, max: usize) callconv(.c) usize {
-    return std.mem.findScalar(wchar_t, str[0..max], 0) orelse max;
+    for (0..max) |i| {
+        if (str[i] == 0) return i;
+    }
+    return max;
 }
 
 fn wcscmp(a: [*:0]const wchar_t, b: [*:0]const wchar_t) callconv(.c) c_int {
diff --git a/lib/std/c.zig b/lib/std/c.zig
index d4f840d4e7b7d426b6bb2736a8634fd7eed57ce9..abadb78976db809b025e6b08e30b5963b9cd95bc 100644
--- a/lib/std/c.zig
+++ b/lib/std/c.zig
@@ -11471,7 +11471,9 @@ pub const strdup = switch (builtin.abi) {
     .msvc => private._strdup,
     else => private.strdup,
 };
+pub extern "c" fn strnlen(s: [*:0]const c_char, n: usize) callconv(.c) usize;
 pub extern "c" fn strndup(s: [*:0]const c_char, n: usize) ?[*:0]c_char;
+pub extern "c" fn wcsnlen(s: [*:0]const wchar_t, n: usize) callconv(.c) usize;
 pub const wcsdup = switch (builtin.abi) {
     .msvc => private._wcsdup,
     else => private.wcsdup,
diff --git a/test/c/string.zig b/test/c/string.zig
index d9f048bbb6a7070c3583912bba96f5198bd5c81a..436333def598445365aa06e59890376d84f91ab7 100644
--- a/test/c/string.zig
+++ b/test/c/string.zig
@@ -50,3 +50,12 @@ test "strndup" {
     const copy3_u8: [*:0]u8 = @ptrCast(copy3);
     try testing.expectEqualStrings("Hello", std.mem.span(@as([*:0]const u8, copy3_u8)));
 }
+
+test "strnlen" {
+    const str: [*:0]const u8 = "Hello";
+    try testing.expectEqual(3, c.strnlen(@ptrCast(str), 3));
+    try testing.expectEqual(4, c.strnlen(@ptrCast(str), 4));
+    try testing.expectEqual(5, c.strnlen(@ptrCast(str), 5));
+    try testing.expectEqual(5, c.strnlen(@ptrCast(str), 6));
+    try testing.expectEqual(5, c.strnlen(@ptrCast(str), 7));
+}
diff --git a/test/c/wchar.zig b/test/c/wchar.zig
index 1c84bd07bece2208d9ab0b1555401496ef28186d..a9e6030ec76b2837121f00d4c8848284c64b6a9b 100644
--- a/test/c/wchar.zig
+++ b/test/c/wchar.zig
@@ -32,3 +32,12 @@ test "wcsdup empty string" {
     defer c.free(cpy);
     try testing.expectEqual(@as(c.wchar_t, 0), cpy[0]);
 }
+
+test "wcsnlen" {
+    const wcs: [*:0]const c.wchar_t = &.{ 'H', 'e', 'l', 'l', 'o' };
+    try testing.expectEqual(3, c.wcsnlen(wcs, 3));
+    try testing.expectEqual(4, c.wcsnlen(wcs, 4));
+    try testing.expectEqual(5, c.wcsnlen(wcs, 5));
+    try testing.expectEqual(5, c.wcsnlen(wcs, 6));
+    try testing.expectEqual(5, c.wcsnlen(wcs, 7));
+}
-- 
2.54.0