9f8eb1ee7
Denys Vlasenko
2016-11-22
Subject
httpd: explain why we use sprintf and why it should be fine
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Commit Diff GitHub →
networking/httpd.c+36 -20
| @@ -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'; | |