ftpd: add idle and absolute timeouts. This is a security issue,

 otherwise ftpd may end up hanging indefinitely.

function                                             old     new   delta
timeout_handler                                        -     110    +110
ftpd_main                                           2019    2115     +96
packed_usage                                       25662   25685     +23
handle_upload_common                                 306     322     +16
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 3/0 up/down: 245/0)             Total: 245 bytes

2 files changed, 52 insertions, 21 deletions

diff --git a/include/usage.h b/include/usage.h
index 25a716278..e78754315 100644
--- a/include/usage.h
+++ b/include/usage.h
@@ -1281,7 +1281,7 @@
      "\n        -f      Force file system check" \
 
 #define ftpd_trivial_usage \
-       "[-wvS] [DIR]"
+       "[-wvS] [-t N] [-T N] [DIR]"
 #define ftpd_full_usage "\n\n" \
        "FTP server\n" \
        "\n" \
@@ -1294,6 +1294,7 @@
      "\n        -w      Allow upload" \
      "\n        -v      Log to stderr" \
      "\n        -S      Log to syslog" \
+     "\n        -t,-T   Idle and absolute timeouts" \
      "\n        DIR     Change root to this directory" \
 
 #define ftpget_trivial_usage \
diff --git a/networking/ftpd.c b/networking/ftpd.c
index 22cec83a8..d63fd9bed 100644
--- a/networking/ftpd.c
+++ b/networking/ftpd.c
@@ -8,11 +8,6 @@
  *
  * Only subset of FTP protocol is implemented but vast majority of clients
  * should not have any problem. You have to run this daemon via inetd.
- *
- * Options:
- * -w   - enable FTP write commands
- *
- * TODO: implement "421 Timeout" thingy (alarm(60) while waiting for a cmd).
  */
 
 #include "libbb.h"
@@ -46,6 +41,7 @@
 #define FTP_GIVEPWORD           331
 #define FTP_RESTOK              350
 #define FTP_RNFROK              350
+#define FTP_TIMEOUT             421
 #define FTP_BADSENDCONN         425
 #define FTP_BADSENDNET          426
 #define FTP_BADSENDFILE         451
@@ -77,12 +73,16 @@ enum {
 )
 
 struct globals {
-        char *p_control_line_buf;
-        len_and_sockaddr *local_addr;
-        len_and_sockaddr *port_addr;
         int pasv_listen_fd;
         int proc_self_fd;
+        int local_file_fd;
+        int start_time;
+        int abs_timeout;
+        int timeout;
+        off_t local_file_pos;
         off_t restart_pos;
+        len_and_sockaddr *local_addr;
+        len_and_sockaddr *port_addr;
         char *ftp_cmd;
         char *ftp_arg;
 #if ENABLE_FEATURE_FTP_WRITE
@@ -179,6 +179,33 @@ cmdio_write_raw(const char *p_text)
         xwrite_str(STDOUT_FILENO, p_text);
 }
 
+static void
+timeout_handler(int sig UNUSED_PARAM)
+{
+        off_t pos;
+        int sv_errno = errno;
+
+        if (monotonic_sec() - G.start_time > G.abs_timeout)
+                goto timed_out;
+
+        if (!G.local_file_fd)
+                goto timed_out;
+
+        pos = xlseek(G.local_file_fd, 0, SEEK_CUR);
+        if (pos == G.local_file_pos)
+                goto timed_out;
+        G.local_file_pos = pos;
+
+        alarm(G.timeout);
+        errno = sv_errno;
+        return;
+
+ timed_out:
+        cmdio_write_raw(STR(FTP_TIMEOUT)" Timeout\r\n");
+/* TODO: do we need to abort (as opposed to usual shutdown) data transfer? */
+        exit(1);
+}
+
 /* Simple commands */
 
 static void
@@ -488,6 +515,7 @@ handle_retr(void)
                 cmdio_write_error(FTP_FILEFAIL);
                 goto file_close_out;
         }
+        G.local_file_fd = local_file_fd;
 
         /* Now deactive O_NONBLOCK, otherwise we have a problem
          * on DMAPI filesystems such as XFS DMAPI.
@@ -506,11 +534,6 @@ handle_retr(void)
         if (remote_fd < 0)
                 goto file_close_out;
 
-/* TODO: if we'll implement timeout, this will need more clever handling.
- * Perhaps alarm(N) + checking that current position on local_file_fd
- * is advancing. As of now, peer may stall us indefinitely.
- */
-
         bytes_transferred = bb_copyfd_eof(local_file_fd, remote_fd);
         close(remote_fd);
         if (bytes_transferred < 0)
@@ -520,6 +543,7 @@ handle_retr(void)
 
  file_close_out:
         close(local_file_fd);
+        G.local_file_fd = 0;
 }
 
 /* List commands */
@@ -753,6 +777,7 @@ handle_upload_common(int is_append, int is_unique)
                         goto close_local_and_bail;
                 return;
         }
+        G.local_file_fd = local_file_fd;
 
         if (offset)
                 xlseek(local_file_fd, offset, SEEK_SET);
@@ -763,11 +788,6 @@ handle_upload_common(int is_append, int is_unique)
         if (remote_fd < 0)
                 goto close_local_and_bail;
 
-/* TODO: if we'll implement timeout, this will need more clever handling.
- * Perhaps alarm(N) + checking that current position on local_file_fd
- * is advancing. As of now, peer may stall us indefinitely.
- */
-
         bytes_transferred = bb_copyfd_eof(remote_fd, local_file_fd);
         close(remote_fd);
         if (bytes_transferred < 0)
@@ -777,6 +797,7 @@ handle_upload_common(int is_append, int is_unique)
 
  close_local_and_bail:
         close(local_file_fd);
+        G.local_file_fd = 0;
 }
 
 static void
@@ -807,6 +828,8 @@ cmdio_get_cmd_and_arg(void)
         uint32_t cmdval;
         char *cmd;
 
+        alarm(G.timeout);
+
         free(G.ftp_cmd);
         len = 8 * 1024; /* Paranoia. Peer may send 1 gigabyte long cmd... */
         G.ftp_cmd = cmd = xmalloc_reads(STDIN_FILENO, NULL, &len);
@@ -878,17 +901,23 @@ int ftpd_main(int argc, char **argv)
 {
         smallint opts;
 
-        opts = getopt32(argv, "l1vS" USE_FEATURE_FTP_WRITE("w"));
+        INIT_G();
+
+        G.start_time = monotonic_sec();
+        G.abs_timeout = 1 * 60 * 60;
+        G.timeout = 2 * 60;
+        opt_complementary = "t+:T+";
+        opts = getopt32(argv, "l1vS" USE_FEATURE_FTP_WRITE("w") "t:T:", &G.timeout, &G.abs_timeout);
 
         if (opts & (OPT_l|OPT_1)) {
                 /* Our secret backdoor to ls */
+                memset(&G, 0, sizeof(G));
 /* TODO: pass -n too? */
                 xchdir(argv[2]);
                 argv[2] = (char*)"--";
                 return ls_main(argc, argv);
         }
 
-        INIT_G();
 
         G.local_addr = get_sock_lsa(STDIN_FILENO);
         if (!G.local_addr) {
@@ -927,6 +956,7 @@ int ftpd_main(int argc, char **argv)
         setsockopt(STDIN_FILENO, SOL_SOCKET, SO_OOBINLINE, &const_int_1, sizeof(const_int_1));
 
         cmdio_write_ok(FTP_GREET);
+        signal(SIGALRM, timeout_handler);
 
 #ifdef IF_WE_WANT_TO_REQUIRE_LOGIN
         {