From c1e7eb738934399737b3a8452ad9b68bb26805d3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Igor=20Anic=CC=81?= <igor.anic@gmail.com>
Date: Mon, 8 Jul 2024 23:37:44 +0200
Subject: [PATCH] crypto.Certificate: case insensitive host name check

This makes comparing host name with dns name from certificate case
insensitive.

I found a few domains (from the
[cloudflare](https://radar.cloudflare.com/domains) list of top domains)
for which tls.Client fails to connect. Error is:

```zig
error: TlsInitializationFailed
Code/zig/lib/std/crypto/Certificate.zig:336:9: 0x1177b1f in verifyHostName (http_get_std)
        return error.CertificateHostMismatch;
Code/zig/lib/std/crypto/tls23/handshake_client.zig:461:25: 0x11752bd in parseServerCertificate (http_get_std)
                        try subject.verifyHostName(opt.host);
```
In its certificate this domains have host names which are not strictly
lower case. This is what checkHostName is comparing:

 |host_name            |  dns_name                |
 |------------------------------------------------|
 |ey.com               | EY.COM                   |
 |truist.com           | Truist.com               |
 |wscampanhas.bradesco | WSCAMPANHAS.BRADESCO     |
 |dell.com             | Dell.com                 |

From
[RFC2818](https://datatracker.ietf.org/doc/html/rfc2818#section-2.4):
>  Matching is performed using the matching rules specified by
   [RFC2459].
From [RFC2459](https://datatracker.ietf.org/doc/html/rfc2459#section-4.2.1.7):
> When comparing URIs, conforming implementations
> MUST compare the scheme and host without regard to case, but assume
> the remainder of the scheme-specific-part is case sensitive.

Testing with:

```
const std = @import("std");

pub fn main() !void {
    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
    const allocator = gpa.allocator();

    const args = try std.process.argsAlloc(allocator);
    defer std.process.argsFree(allocator, args);

    if (args.len > 1) {
        const domain = args[1];

        var client: std.http.Client = .{ .allocator = allocator };
        defer client.deinit();

        // Add https:// prefix if needed
        const url = brk: {
            const scheme = "https://";
            if (domain.len >= scheme.len and std.mem.eql(u8, domain[0..scheme.len], scheme))
                break :brk domain;

            var url_buf: [128]u8 = undefined;
            break :brk try std.fmt.bufPrint(&url_buf, "https://{s}", .{domain});
        };

        const uri = try std.Uri.parse(url);
        var server_header_buffer: [16 * 1024]u8 = undefined;
        var req = try client.open(.GET, uri, .{ .server_header_buffer = &server_header_buffer });
        defer req.deinit();

        try req.send();
        try req.wait();
    }
}
```
`$ zig run example/main.zig -- truist.com `
---
 lib/std/crypto/Certificate.zig | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/lib/std/crypto/Certificate.zig b/lib/std/crypto/Certificate.zig
index 1e3bb9ca0b..9ddd587a19 100644
--- a/lib/std/crypto/Certificate.zig
+++ b/lib/std/crypto/Certificate.zig
@@ -345,7 +345,7 @@ pub const Parsed = struct {
     // component or component fragment. E.g., *.a.com matches foo.a.com but
     // not bar.foo.a.com. f*.com matches foo.com but not bar.com.
     fn checkHostName(host_name: []const u8, dns_name: []const u8) bool {
-        if (mem.eql(u8, dns_name, host_name)) {
+        if (std.ascii.eqlIgnoreCase(dns_name, host_name)) {
             return true; // exact match
         }
 
@@ -362,7 +362,7 @@ pub const Parsed = struct {
 
             // If not a wildcard and they dont
             // match then there is no match.
-            if (mem.eql(u8, dns.?, "*") == false and mem.eql(u8, dns.?, host.?) == false) {
+            if (mem.eql(u8, dns.?, "*") == false and std.ascii.eqlIgnoreCase(dns.?, host.?) == false) {
                 return false;
             }
         };
@@ -381,6 +381,9 @@ test "Parsed.checkHostName" {
     try expectEqual(false, Parsed.checkHostName("foo.bar.ziglang.org", "*.ziglang.org"));
     try expectEqual(false, Parsed.checkHostName("ziglang.org", "zig*.org"));
     try expectEqual(false, Parsed.checkHostName("lang.org", "zig*.org"));
+    // host name check should be case insensitive
+    try expectEqual(true, Parsed.checkHostName("ziglang.org", "Ziglang.org"));
+    try expectEqual(true, Parsed.checkHostName("bar.ziglang.org", "*.Ziglang.ORG"));
 }
 
 pub const ParseError = der.Element.ParseElementError || ParseVersionError || ParseTimeError || ParseEnumError || ParseBitStringError;