httpd: add -M MAXCONN - do not accept unlimited number of connections

We were lacking even basic rate-limiting.

function                                             old     new   delta
httpd_main                                           648     915    +267
handle_incoming_and_exit                            2235    2264     +29
packed_usage                                       35868   35894     +26
cgi_io_loop_and_exit                                 537     552     +15
send_headers                                         704     712      +8
get_line                                             106     108      +2
.rodata                                           106829  106830      +1
send_file_and_exit                                   890     887      -3
mini_httpd                                           161       -    -161
------------------------------------------------------------------------------
(add/remove: 0/1 grow/shrink: 7/1 up/down: 348/-164)          Total: 184 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 86 insertions, 19 deletions

diff --git a/networking/httpd.c b/networking/httpd.c
index 49f60d967..39a7046f5 100644
--- a/networking/httpd.c
+++ b/networking/httpd.c
@@ -267,6 +267,7 @@
 //usage:       "[-ifv[v]]"
 //usage:       " [-c CONFFILE]"
 //usage:       " [-p [IP:]PORT]"
+//usage:       " [-M MAXCONN]"
 //usage:        IF_FEATURE_HTTPD_SETUID(" [-u USER[:GRP]]")
 //usage:        IF_FEATURE_HTTPD_BASIC_AUTH(" [-r REALM]")
 //usage:       " [-h HOME]\n"
@@ -277,6 +278,7 @@
 //usage:     "\n        -f              Run in foreground"
 //usage:     "\n        -v[v]           Verbose"
 //usage:     "\n        -p [IP:]PORT    Bind to IP:PORT (default *:"STR(CONFIG_FEATURE_HTTPD_PORT_DEFAULT)")"
+//usage:     "\n        -M NUM          Pause if NUM connections are open (default 256)"
 //usage:        IF_FEATURE_HTTPD_SETUID(
 //usage:     "\n        -u USER[:GRP]   Set uid/gid after binding to port")
 //usage:        IF_FEATURE_HTTPD_BASIC_AUTH(
@@ -479,6 +481,8 @@ struct globals {
         IF_FEATURE_HTTPD_BASIC_AUTH(char *remoteuser;)
 
         pid_t parent_pid;
+        int children_fd;
+        int conn_limit;
 
         off_t file_size;        /* -1 - unknown */
 #if ENABLE_FEATURE_HTTPD_RANGES
@@ -494,7 +498,6 @@ struct globals {
 #if ENABLE_FEATURE_HTTPD_CONFIG_WITH_SCRIPT_INTERPR
         Htaccess *script_i;     /* config script interpreters */
 #endif
-        char *iobuf;            /* [IOBUF_SIZE] */
 #define        hdr_buf bb_common_bufsiz1
 #define sizeof_hdr_buf COMMON_BUFSIZE
         char *hdr_ptr;
@@ -508,6 +511,7 @@ struct globals {
 #if ENABLE_FEATURE_HTTPD_PROXY
         Htaccess_Proxy *proxy;
 #endif
+        char iobuf[IOBUF_SIZE];
 };
 #define G (*ptr_to_globals)
 #define verbose           (G.verbose          )
@@ -543,11 +547,11 @@ enum {
 #define g_auth            (G.g_auth           )
 #define mime_a            (G.mime_a           )
 #define script_i          (G.script_i         )
-#define iobuf             (G.iobuf            )
 #define hdr_ptr           (G.hdr_ptr          )
 #define hdr_cnt           (G.hdr_cnt          )
 #define http_error_page   (G.http_error_page  )
 #define proxy             (G.proxy            )
+#define iobuf             (G.iobuf            )
 #define INIT_G() do { \
         setup_common_bufsiz(); \
         SET_PTR_TO_GLOBALS(xzalloc(sizeof(G))); \
@@ -1045,7 +1049,8 @@ static void decodeBase64(char *data)
  */
 static int openServer(void)
 {
-        unsigned n = bb_strtou(bind_addr_or_port, NULL, 10);
+        unsigned n;
+        n = bb_strtou(bind_addr_or_port, NULL, 10);
         if (!errno && n && n <= 0xffff)
                 n = create_and_bind_stream_or_die(NULL, n);
         else
@@ -2227,10 +2232,6 @@ static void handle_incoming_and_exit(const len_and_sockaddr *fromAddr)
 #endif
         char *HTTP_slash;
 
-        /* Allocation of iobuf is postponed until now
-         * (IOW, server process doesn't need to waste 8k) */
-        iobuf = xmalloc(IOBUF_SIZE);
-
         if (ENABLE_FEATURE_HTTPD_CGI || DEBUG || verbose) {
                 /* NB: can be NULL (user runs httpd -i by hand?) */
                 rmt_ip_str = xmalloc_sockaddr2dotted(&fromAddr->u.sa);
@@ -2643,6 +2644,57 @@ static void handle_incoming_and_exit(const len_and_sockaddr *fromAddr)
         );
 }
 
+static int count_children(void)
+{
+        int count;
+        int sz = pread(G.children_fd, iobuf, IOBUF_SIZE - 1, 0);
+        if (sz < 0)
+                return -1;
+        /* The actual format is "NUM NUM ", but future-proof for lack of last space, and for '\n' */
+        count = 0;
+        if (sz > 0) {
+                char *p = iobuf;
+                iobuf[sz] = '\n';
+                do {
+                        if (*++p == ' ')
+                                count++, p++;
+                } while (*p != '\n');
+                if (p[-1] != ' ') /* it was "NUM NUM\n" (not "NUM NUM \n")? */
+                        count++; /* there were (NUMSPACES + 1) pids */
+        }
+        return count;
+}
+
+static int throttle_if_conn_limit(void)
+{
+        unsigned usec = 0xffff; /* 0.065535 seconds */
+        int countdown, c;
+        for (;;) {
+                countdown = G.conn_limit;
+                c = count_children();
+                if (c < 0)
+                        break; /* can't count them */
+                countdown -= c;
+                if (countdown <= 0) { /* we are at MAXCONN, pause until we are below */
+                        bb_error_msg("pausing, children:%u", c);
+                        //bb_error_msg("pausing %ums, children:%u", usec/1000, c);
+                        usleep(usec);
+                        usec = ((usec << 1) | 1) & 0x1fffff; /* x2, up to 2.097151 seconds */
+                        continue; /* loop: count them again */
+                }
+                if (VERBOSE_3) /* -vvv periodically shows # of children */
+                        bb_error_msg("children:%u", c ? c - 1 : c);
+// "Why minus one?!" you ask. We _just now_ forked (see the caller)
+// and immediately checked the # of children.
+// Of course, the just-forked child did not have time to complete.
+// Without "minus one" hack, this causes above statement to always show
+// at least one child, gives wrong impression to the log's reader
+// (looks like one child is stuck).
+                break;
+        }
+        return countdown;
+}
+
 /*
  * The main http server function.
  * Given a socket, listen for new connections and farm out
@@ -2653,16 +2705,22 @@ static void handle_incoming_and_exit(const len_and_sockaddr *fromAddr)
 static void mini_httpd(int server_socket) NORETURN;
 static void mini_httpd(int server_socket)
 {
+        int countdown;
+
         xmove_fd(server_socket, 0);
         /* NB: it's best to not use xfuncs in this loop before fork().
          * Otherwise server may die on transient errors (temporary
          * out-of-memory condition, etc), which is Bad(tm).
          * Try to do any dangerous calls after fork.
          */
+        countdown = G.conn_limit;
         while (1) {
                 int n;
                 len_and_sockaddr fromAddr;
 
+                if (G.children_fd > 0 && --countdown < 0)
+                        countdown = throttle_if_conn_limit();
+
                 /* Wait for connections... */
                 fromAddr.len = LSA_SIZEOF_SA;
                 n = accept(0, &fromAddr.u.sa, &fromAddr.len);
@@ -2698,6 +2756,7 @@ static void mini_httpd(int server_socket)
 static void mini_httpd_nommu(int server_socket, int argc, char **argv) NORETURN;
 static void mini_httpd_nommu(int server_socket, int argc, char **argv)
 {
+        int countdown;
         char *argv_copy[argc + 2];
 
         argv_copy[0] = argv[0];
@@ -2710,9 +2769,13 @@ static void mini_httpd_nommu(int server_socket, int argc, char **argv)
          * out-of-memory condition, etc), which is Bad(tm).
          * Try to do any dangerous calls after fork.
          */
+        countdown = G.conn_limit;
         while (1) {
                 int n;
 
+                if (G.children_fd > 0 && --countdown < 0)
+                        countdown = throttle_if_conn_limit();
+
                 /* Wait for connections... */
                 n = accept(0, NULL, NULL);
                 if (n < 0)
@@ -2774,9 +2837,10 @@ enum {
         IF_FEATURE_HTTPD_AUTH_MD5(      m_opt_md5       ,)
         IF_FEATURE_HTTPD_SETUID(        u_opt_setuid    ,)
         p_opt_port      ,
-        p_opt_inetd     ,
-        p_opt_foreground,
-        p_opt_verbose   ,
+        M_opt_maxconn   ,
+        i_opt_inetd     ,
+        f_opt_foreground,
+        v_opt_verbose   ,
         OPT_CONFIG_FILE = 1 << c_opt_config_file,
         OPT_DECODE_URL  = 1 << d_opt_decode_url,
         OPT_HOME_HTTPD  = 1 << h_opt_home_httpd,
@@ -2785,9 +2849,9 @@ enum {
         OPT_MD5         = IF_FEATURE_HTTPD_AUTH_MD5(      (1 << m_opt_md5       )) + 0,
         OPT_SETUID      = IF_FEATURE_HTTPD_SETUID(        (1 << u_opt_setuid    )) + 0,
         OPT_PORT        = 1 << p_opt_port,
-        OPT_INETD       = 1 << p_opt_inetd,
-        OPT_FOREGROUND  = 1 << p_opt_foreground,
-        OPT_VERBOSE     = 1 << p_opt_verbose,
+        OPT_INETD       = 1 << i_opt_inetd,
+        OPT_FOREGROUND  = 1 << f_opt_foreground,
+        OPT_VERBOSE     = 1 << v_opt_verbose,
 };
 
 
@@ -2809,6 +2873,7 @@ int httpd_main(int argc UNUSED_PARAM, char **argv)
         setlocale(LC_TIME, "C");
 #endif
 
+        G.conn_limit = 256;
         home_httpd = xrealloc_getcwd_or_warn(NULL);
         /* We do not "absolutize" path given by -h (home) opt.
          * If user gives relative path in -h,
@@ -2819,7 +2884,7 @@ int httpd_main(int argc UNUSED_PARAM, char **argv)
                         IF_FEATURE_HTTPD_BASIC_AUTH("r:")
                         IF_FEATURE_HTTPD_AUTH_MD5("m:")
                         IF_FEATURE_HTTPD_SETUID("u:")
-                        "p:ifv"
+                        "p:M:+ifv"
                         "\0"
                         /* -v counts, -i implies -f */
                         "vv:if",
@@ -2829,6 +2894,7 @@ int httpd_main(int argc UNUSED_PARAM, char **argv)
                         IF_FEATURE_HTTPD_AUTH_MD5(, &pass)
                         IF_FEATURE_HTTPD_SETUID(, &s_ugid)
                         , &bind_addr_or_port
+                        , &G.conn_limit
                         , &verbose
                 );
         if (opt & OPT_DECODE_URL) {
@@ -2871,6 +2937,10 @@ int httpd_main(int argc UNUSED_PARAM, char **argv)
                 xchdir(home_httpd);
 
         if (!(opt & OPT_INETD)) {
+                G.parent_pid = getpid();
+                sprintf(iobuf, "/proc/self/task/%u/children", (unsigned)G.parent_pid);
+                G.children_fd = open(iobuf, O_RDONLY | O_CLOEXEC);
+
                 /* Make it unnecessary to wait for children */
                 signal(SIGCHLD, SIG_IGN);
 
@@ -2905,16 +2975,13 @@ int httpd_main(int argc UNUSED_PARAM, char **argv)
 //                      setenv_long("SERVER_PORT", ???);
         }
 #endif
-
         parse_conf(DEFAULT_PATH_HTTPD_CONF, FIRST_PARSE);
-        if (!(opt & OPT_INETD)) {
-                G.parent_pid = getpid();
-                signal(SIGHUP, sighup_handler);
-        }
 
         xfunc_error_retval = 0;
         if (opt & OPT_INETD)
                 mini_httpd_inetd(); /* never returns */
+
+        signal(SIGHUP, sighup_handler);
 #if BB_MMU
         if (!(opt & OPT_FOREGROUND))
                 bb_daemonize(0); /* don't change current directory */