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httpd: explain why we use sprintf and why it should be fine

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While at it, fix a pathological case where it is not fine:
-r REALM with some 8-kbyte long REALM would overflow the buffer.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko 2016-11-22 02:23:35 +01:00
parent 7e8218f9b2
commit 9f8eb1ee76
1 changed files with 36 additions and 20 deletions
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56
networking/httpd.c
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@ -926,16 +926,16 @@ static void log_and_exit(void)
static void send_headers(int responseNum)
{
static const char RFC1123FMT[] ALIGN1 = "%a, %d %b %Y %H:%M:%S GMT";
/* Fixed size 29-byte string. Example: Sun, 06 Nov 1994 08:49:37 GMT */
char date_str[40]; /* using a bit larger buffer to paranoia reasons */
const char *responseString = "";
const char *infoString = NULL;
const char *mime_type;
#if ENABLE_FEATURE_HTTPD_ERROR_PAGES
const char *error_page = NULL;
#endif
unsigned i;
time_t timer = time(NULL);
char tmp_str[80];
int len;
for (i = 0; i < ARRAY_SIZE(http_response_type); i++) {
@ -948,25 +948,33 @@ static void send_headers(int responseNum)
break;
}
}
/* error message is HTML */
mime_type = responseNum == HTTP_OK ?
found_mime_type : "text/html";
if (verbose)
bb_error_msg("response:%u", responseNum);
/* emit the current date */
strftime(tmp_str, sizeof(tmp_str), RFC1123FMT, gmtime(&timer));
/* We use sprintf, not snprintf (it's less code).
* iobuf[] is several kbytes long and all headers we generate
* always fit into those kbytes.
*/
strftime(date_str, sizeof(date_str), RFC1123FMT, gmtime(&timer));
len = sprintf(iobuf,
"HTTP/1.0 %d %s\r\nContent-type: %s\r\n"
"Date: %s\r\nConnection: close\r\n",
responseNum, responseString, mime_type, tmp_str);
"HTTP/1.0 %d %s\r\n"
"Content-type: %s\r\n"
"Date: %s\r\n"
"Connection: close\r\n",
responseNum, responseString,
/* if it's error message, then it's HTML */
(responseNum == HTTP_OK ? found_mime_type : "text/html"),
date_str
);
#if ENABLE_FEATURE_HTTPD_BASIC_AUTH
if (responseNum == HTTP_UNAUTHORIZED) {
len += sprintf(iobuf + len,
"WWW-Authenticate: Basic realm=\"%s\"\r\n",
g_realm);
"WWW-Authenticate: Basic realm=\"%.999s\"\r\n",
g_realm /* %.999s protects from overflowing iobuf[] */
);
}
#endif
if (responseNum == HTTP_MOVED_TEMPORARILY) {
@ -981,7 +989,8 @@ static void send_headers(int responseNum)
"Location: %s/%s%s\r\n",
found_moved_temporarily,
(g_query ? "?" : ""),
(g_query ? g_query : ""));
(g_query ? g_query : "")
);
if (len > IOBUF_SIZE-3)
len = IOBUF_SIZE-3;
}
@ -1002,13 +1011,15 @@ static void send_headers(int responseNum)
#endif
if (file_size != -1) { /* file */
strftime(tmp_str, sizeof(tmp_str), RFC1123FMT, gmtime(&last_mod));
strftime(date_str, sizeof(date_str), RFC1123FMT, gmtime(&last_mod));
#if ENABLE_FEATURE_HTTPD_RANGES
if (responseNum == HTTP_PARTIAL_CONTENT) {
len += sprintf(iobuf + len, "Content-Range: bytes %"OFF_FMT"u-%"OFF_FMT"u/%"OFF_FMT"u\r\n",
len += sprintf(iobuf + len,
"Content-Range: bytes %"OFF_FMT"u-%"OFF_FMT"u/%"OFF_FMT"u\r\n",
range_start,
range_end,
file_size);
file_size
);
file_size = range_end - range_start + 1;
}
#endif
@ -1016,8 +1027,9 @@ static void send_headers(int responseNum)
#if ENABLE_FEATURE_HTTPD_RANGES
"Accept-Ranges: bytes\r\n"
#endif
"Last-Modified: %s\r\n%s %"OFF_FMT"u\r\n",
tmp_str,
"Last-Modified: %s\r\n"
"%s %"OFF_FMT"u\r\n",
date_str,
content_gzip ? "Transfer-length:" : "Content-length:",
file_size
);
@ -1031,9 +1043,13 @@ static void send_headers(int responseNum)
if (infoString) {
len += sprintf(iobuf + len,
"<HTML><HEAD><TITLE>%d %s</TITLE></HEAD>\n"
"<BODY><H1>%d %s</H1>\n%s\n</BODY></HTML>\n",
"<BODY><H1>%d %s</H1>\n"
"%s\n"
"</BODY></HTML>\n",
responseNum, responseString,
responseNum, responseString, infoString);
responseNum, responseString,
infoString
);
}
if (DEBUG) {
iobuf[len] = '\0';