Boa Web Server 缺陷报告及其修正方法
综述Boa 作为一种轻巧实用的 WEB 服务器广泛应用于嵌入式设备上,
但 Boa 对实现动态网页的 CGI的支持上仍存在一些缺陷,
本文描述了 Boa 对 CGI 的 Status/Location 的支持的缺陷及其修正方法.
版本: 所有版本 (0.94.13)
缺陷: BOA 解析 CGI 应答头时不能完整处理 Status 和 Location
缺陷描述:
CGI/1.1 标准规定, CGI 脚本可以通过 Status 设置 HTTP 应答状态(如, Status: 500 Internal Error) 和
Location 进行地址重定向 (如, Location: www.xxx.com), 而不管它们在应答头中的位置.
Boa 支持 Stauts 和 Location 两种应答头, 但它的实现仅能正确处理 Stauts 和 Location 在应答第一行的
CGI 应答. 这将给 CGI 程序的移植带来很多不便, 进而影响 Boa 作为Web Server 的功能的发挥.
影响功能:
ASP/PHP/JSP/Perl/... 等的 header, redirect, ... 等都会应用到 Stauts/Location 进行设置应答状态和
地址重定向. Boa 的该实现将影响 CGI 脚本正常功能的使用.
缺陷功能对比(对Status/Location的支持程序):
Apache 1.3.x/2.x IIS 4.x/5.x/6.X Boa 0.9x thttpd mini-httpd
完全支持 完全支持 * 部分支持 完全支持 完全支持
[ 本帖最后由 newzy 于 2006-9-7 18:02 编辑 ]
缺陷分析
缺陷分析CGI 应用程序进行应答时, 可以 HTTP 头进行有限的控制. 如,设置客户端不缓存页面可用下面的 C 脚本,
HTTP/1.0: printf("Pragma: no-cache\n"); 或
HTTP/1.1: printf("Cache-Control: no-cache; no-store\n");
如果, 同时还需要告诉浏览器进行设置 Cookie 和控制相应状态(200 OK) 或地址重定向,
那么就必须输出多行 http 头控制语句, CGI 支持两个解析头 "Status: " 和 "Loction: ",
即协议规定, Web 服务器支持解析头时能使用 "Status: " 进行应答状态控制, 使用 "Location: " 进行地址重定向,
并为应答添加状态头 "HTTP/1.0 302 Moved Temporarily\n" 或 "HTTP/1.1 302 Found\n".
而不管它们在 CGI 应答头的什么位置.
分析 Boa Source Code:
cgi_header.cLine 82-136 容易发现, Boa 只解析 CGI 应答的第一行, 是否为 "Status: ", "Location: ", 如下所示
23
24 int process_cgi_header(request * req)
25 {
26 char *buf;
27 char *c;
28
29 if (req->cgi_status != CGI_DONE)
30 req->cgi_status = CGI_BUFFER;
31
32 buf = req->header_line;
33
34 c = strstr(buf, "\n\r\n");
35 if (c == NULL) {
36 c = strstr(buf, "\n\n");
37 if (c == NULL) {
38 log_error_time();
39 fputs("cgi_header: unable to find LFLF\n", stderr);
40 #ifdef FASCIST_LOGGING
41 log_error_time();
42 fprintf(stderr, "\"%s\"\n", buf);
43 #endif
44 send_r_bad_gateway(req);
45 return 0;
46 }
47 }
48 if (req->simple) {
49 if (*(c + 1) == '\r')
50 req->header_line = c + 2;
51 else
52 req->header_line = c + 1;
53 return 1;
54 }
55 if (!strncasecmp(buf, "Status: ", 8)) {
56 req->header_line--;
57 memcpy(req->header_line, "HTTP/1.0 ", 9);
58 } else if (!strncasecmp(buf, "Location: ", 10)) { /* got a location header */
59 #ifdef FASCIST_LOGGING
60
61 log_error_time();
62 fprintf(stderr, "%s:%d - found Location header \"%s\"\n",
63 __FILE__, __LINE__, buf + 10);
64 #endif
65
66
67 if (buf == '/') { /* virtual path */
68 log_error_time();
69 fprintf(stderr,
70 "server does not support internal redirection: " \
71 "\"%s\"\n", buf + 10);
72 send_r_bad_request(req);
73
74 /*
75 * We (I, Jon) have declined to support absolute-path parsing
76 * because I see it as a major security hole.
77 * Location: /etc/passwd or Location: /etc/shadow is not funny.
78 *
79 * Also, the below code is borked.
80 * request_uri could contain /cgi-bin/bob/extra_path
81 */
82
83 /*
84 strcpy(req->request_uri, buf + 10);
85 return internal_redirect(req);
86 */
87 } else { /* URL */
88 char *c2;
89 c2 = strchr(buf + 10, '\n');
90 /* c2 cannot ever equal NULL here because we already have found one */
91
92 --c2;
93 while (*c2 == '\r')
94 --c2;
95 ++c2;
96 /* c2 now points to a '\r' or the '\n' */
97 *c2++ = '\0'; /* end header */
98
99 /* first next header, or is at req->header_end */
100 while ((*c2 == '\n' || *c2 == '\r') && c2 < req->header_end)
101 ++c2;
102 if (c2 == req->header_end)
103 send_r_moved_temp(req, buf + 10, "");
104 else
105 send_r_moved_temp(req, buf + 10, c2);
106 }
107 req->status = DONE;
108 return 1;
109 } else { /* not location and not status */
110 char *dest;
111 int howmuch;
112 send_r_request_ok(req); /* does not terminate */
113 /* got to do special things because
114 a) we have a single buffer divided into 2 pieces
115 b) we need to merge those pieces
116 Easiest way is to memmove the cgi data backward until
117 it touches the buffered data, then reset the cgi data pointers
118 */
119 dest = req->buffer + req->buffer_end;
120 if (req->method == M_HEAD) {
121 if (*(c + 1) == '\r')
122 req->header_end = c + 2;
123 else
124 req->header_end = c + 1;
125 req->cgi_status = CGI_DONE;
126 }
127 howmuch = req->header_end - req->header_line;
128
129 if (dest + howmuch > req->buffer + BUFFER_SIZE) {
130 /* big problem */
131 log_error_time();
130 fprintf(stderr, "Too much data to move! Aborting! %s %d\n",
131 __FILE__, __LINE__);
132 /* reset buffer pointers because we already called
133 send_r_request_ok... */
134 req->buffer_start = req->buffer_end = 0;
135 send_r_error(req);
136 return 0;
137 }
138 memmove(dest, req->header_line, howmuch);
139 req->buffer_end += howmuch;
140 req->header_line = req->buffer + req->buffer_end;
141 req->header_end = req->header_line;
142 req_flush(req);
143 if (req->method == M_HEAD)
144 return 0;
145 }
146 return 1;
147}
148
149
修正方法
CGI 应答头包括多行, 我们必须对其进行逐行分析, 并作出正确的应答.
下面是修改好的源程序, 即将原来的 82-136 (即相当下文#else, #endif内部分) 替换成如下代码:
#if 1
while(1) {
int len;
char * pnext = NULL;
char * ptmp = NULL;
/* not find HTTP header tailer */
if (NULL == (pnext=strchr(buf, '\n'))) /* has no '\n' */
break;
/* the length of this line,
* include '\n'
*/
len = pnext - buf + 1;
if (!strncasecmp(buf, "Location: ", 10)) { /* got a location header */
/* not the first one
* exchange this line to the first line
*/
if (buf != req->header_line)
{
if (NULL == (ptmp=(char *)malloc(len)))
{
log_error_time();
perror("malloc");
send_r_error(req);
return 0;
}
/* move Status: to line header */
memcpy(ptmp, buf, len);
memmove(req->header_line+len, req->header_line, buf-req->header_line);
memcpy(req->header_line, ptmp, len);
free(ptmp);
}
/* force pointer header */
buf = req->header_line;
#ifdef FASCIST_LOGGING
log_error_time();
fprintf(stderr, "%s:%d - found Location header \"%s\"\n",
__FILE__, __LINE__, buf + 10);
#endif
if (buf == '/') { /* virtual path */
log_error_time();
fprintf(stderr,
"server does not support internal redirection: " \
"\"%s\"\n", buf + 10);
send_r_bad_request(req);
/*
* We (I, Jon) have declined to support absolute-path parsing
* because I see it as a major security hole.
* Location: /etc/passwd or Location: /etc/shadow is not funny.
*
* Also, the below code is borked.
* request_uri could contain /cgi-bin/bob/extra_path
*/
/*
strcpy(req->request_uri, buf + 10);
return internal_redirect(req);
*/
} else { /* URL */
char *c2;
c2 = strchr(buf + 10, '\n');
/* c2 cannot ever equal NULL here because we already have found one */
--c2;
while (*c2 == '\r')
--c2;
++c2;
/* c2 now points to a '\r' or the '\n' */
*c2++ = '\0'; /* end header */
/* first next header, or is at req->header_end */
while ((*c2 == '\n' || *c2 == '\r') && c2 < req->header_end)
++c2;
if (c2 == req->header_end)
send_r_moved_temp(req, buf + 10, "");
else
send_r_moved_temp(req, buf + 10, c2);
}
req->status = DONE;
return 1;
}else if (!strncasecmp(buf, "Status: ", 8)) {
/* not the first one
* exchange this line to the first line
*/
if (buf != req->header_line)
{
if (NULL == (ptmp=(char *)malloc(len)))
{
log_error_time();
perror("malloc");
send_r_error(req);
return 0;
}
/* move Status: to line header */
memcpy(ptmp, buf, len);
memmove(req->header_line+len, req->header_line, buf-req->header_line);
memcpy(req->header_line, ptmp, len);
free(ptmp);
}
req->header_line--;
memcpy(req->header_line, "HTTP/1.0 ", 9);
return 1;
}
/* pointer to next line */
buf = pnext + 1;
/* reach the end of HTTP header */
if ('\0' == buf || '\n' == buf || '\r' == buf)
break;
}
if (1) { /* always done */
#else
if (!strncasecmp(buf, "Status: ", 8)) {
req->header_line--;
memcpy(req->header_line, "HTTP/1.0 ", 9);
} else if (!strncasecmp(buf, "Location: ", 10)) { /* got a location header */
#ifdef FASCIST_LOGGING
log_error_time();
fprintf(stderr, "%s:%d - found Location header \"%s\"\n",
__FILE__, __LINE__, buf + 10);
#endif
if (buf == '/') { /* virtual path */
log_error_time();
fprintf(stderr,
"server does not support internal redirection: " \
"\"%s\"\n", buf + 10);
send_r_bad_request(req);
/*
* We (I, Jon) have declined to support absolute-path parsing
* because I see it as a major security hole.
* Location: /etc/passwd or Location: /etc/shadow is not funny.
*
* Also, the below code is borked.
* request_uri could contain /cgi-bin/bob/extra_path
*/
/*
strcpy(req->request_uri, buf + 10);
return internal_redirect(req);
*/
} else { /* URL */
char *c2;
c2 = strchr(buf + 10, '\n');
/* c2 cannot ever equal NULL here because we already have found one */
--c2;
while (*c2 == '\r')
--c2;
++c2;
/* c2 now points to a '\r' or the '\n' */
*c2++ = '\0'; /* end header */
/* first next header, or is at req->header_end */
while ((*c2 == '\n' || *c2 == '\r') && c2 < req->header_end)
++c2;
if (c2 == req->header_end)
send_r_moved_temp(req, buf + 10, "");
else
send_r_moved_temp(req, buf + 10, c2);
}
req->status = DONE;
return 1;
} else { /* not location and not status */
#endif
老大..佩服中..顶一下.. 厉害。。。。 我喜欢看unified diff……;P 好贴!!!!!!!!!!!!!! 2006年9月，那年我刚上大学。。。2012年4月，我遇到了这个问题。。。:mrgreen: 兄台！！！感谢啊！！！啥也不说了！！:'(
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