git.seregonwar.com

src/http_csrf.c

zftpd / src / http_csrf.c

1	/*
2	MIT License
3
4	Copyright (c) 2026 Seregon
5
6	Permission is hereby granted, free of charge, to any person obtaining a copy
7	of this software and associated documentation files (the "Software"), to deal
8	in the Software without restriction, including without limitation the rights
9	to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10	copies of the Software, and to permit persons to whom the Software is
11	furnished to do so, subject to the following conditions:
12
13	The above copyright notice and this permission notice shall be included in all
14	copies or substantial portions of the Software.
15
16	THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17	IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18	FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
19	AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20	LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21	OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22	SOFTWARE.
23	*/
24
25	/**
26	* @file http_csrf.c
27	* @brief CSRF Protection Implementation
28	*/
29
30	#include "http_csrf.h"
31	#include "http_config.h"
32	#include <fcntl.h>
33	#include <stdio.h>
34	#include <string.h>
35	#include <unistd.h>
36
37	#if ENABLE_WEB_UPLOAD
38
39	/* Global CSRF token storage (32 hex chars + null) */
40	static char g_csrf_token[HTTP_CSRF_TOKEN_LENGTH + 1];
41	static int g_csrf_initialized = 0;
42
43	int http_csrf_init(void) {
44	g_csrf_token[0] = '\0';
45	g_csrf_initialized = 0;
46	int fd = open("/dev/urandom", O_RDONLY);
47	if (fd < 0) {
48	/*
49	* VULN-03 fix: fail hard instead of falling back to a
50	* predictable token. Empty token -> all uploads rejected.
51	*
52	* BEFORE: snprintf(g_csrf_token, ..., "0123456789abcdef...");
53	* AFTER: g_csrf_token[0] = '\0'; (all requests fail)
54	*/
55	g_csrf_token[0] = '\0';
56	return -1;
57	}
58
59	unsigned char random_bytes[HTTP_CSRF_TOKEN_LENGTH / 2];
60	if (read(fd, random_bytes, sizeof(random_bytes)) != sizeof(random_bytes)) {
61	close(fd);
62	/* Partial read -> unusable entropy, fail hard */
63	g_csrf_token[0] = '\0';
64	return -1;
65	}
66	close(fd);
67
68	/* Convert to hex string */
69	for (int i = 0; i < HTTP_CSRF_TOKEN_LENGTH / 2; i++) {
70	size_t offset = (size_t)i * 2U;
71	size_t remaining = sizeof(g_csrf_token) - offset;
72	if (remaining < 3U) {
73	/* Buffer exhausted during conversion, fail hard */
74	g_csrf_token[0] = '\0';
75	return -1;
76	}
77	int n = snprintf(g_csrf_token + offset, remaining, "%02x", random_bytes[i]);
78	if ((n < 0) \|\| (n >= (int)remaining)) {
79	g_csrf_token[0] = '\0';
80	return -1;
81	}
82	}
83
84	g_csrf_initialized = 1;
85	return 0;
86	}
87
88	const char *http_csrf_get_token(void) { return g_csrf_token; }
89
90	int http_csrf_validate(const http_request_t *req) {
91	if (req == NULL) {
92	return -1;
93	}
94
95	/*
96	* Phase 1.2: use explicit initialization flag instead of
97	* testing token emptiness. More readable and unforgeable.
98	*/
99	if (g_csrf_initialized == 0) {
100	return -1;
101	}
102
103	/* Look for X-CSRF-Token header */
104	const char *token = NULL;
105	for (size_t i = 0; i < req->num_headers; i++) {
106	if (strcasecmp(req->headers[i].name, "X-CSRF-Token") == 0) {
107	token = req->headers[i].value;
108	break;
109	}
110	}
111
112	if (token == NULL) {
113	return -1;
114	}
115
116	if (strcmp(token, g_csrf_token) != 0) {
117	return -1;
118	}
119
120	return 0;
121	}
122
123	#else
124
125	/* No-op implementations when upload is disabled */
126	void http_csrf_init(void) {}
127	const char *http_csrf_get_token(void) { return ""; }
128	int http_csrf_validate(const http_request_t *req) {
129	(void)req;
130	return 0;
131	}
132
133	#endif /* ENABLE_WEB_UPLOAD */
134

Seregon/zftpd