misc.c

   1 /*
   2  * User FTP Server
   3  * Author : C2H5OH
   4  * License: GPL v2
   5  *
   6  * misc.c - Miscellaneous helper functions.
   7  */
   8
   9 #include "uftps.h"
  10
  11 /*
  12  * fatal
  13  *
  14  * Show 'msg' followed by the system error and exit badly.
  15  */
  16 void fatal (char *msg)
  17 {
  18         fputs("FATAL ERROR: ", stderr);
  19         perror(msg);
  20         exit(EXIT_FAILURE);
  21 }
  22
  23
  24 /*
  25  * send_reply
  26  *
  27  * Send 'msg' through socket 'sk'. Because a single send() call doesn't ensure
  28  * that all data is transferred (or maybe the call is interrupted), we need to
  29  * place it in a small loop to wait until all 'msg' contents, at least, gets
  30  * copied onto the internal TCP/IP stack buffers.
  31  */
  32 void send_reply (int sk, char *msg)
  33 {
  34         int msglen, b;
  35
  36         debug_msg("<<< %s", msg);
  37
  38         msglen = strlen(msg);
  39         do {
  40                 b = send(sk, msg, msglen, 0);
  41                 if (b == -1)
  42                         fatal("Could not send reply");
  43                 msg    += b;
  44                 msglen -= b;
  45         } while (msglen > 0);
  46
  47 }
  48
  49
  50 #if 0
  51 /*
  52  * str_to_ll
  53  *
  54  * Converts a string to its numeric value in 64 bit representation. Quote from
  55  * sysutil.c file of VsFTPd:
  56  *
  57  *   ``atoll() is C99 standard - but even modern FreeBSD, OpenBSD don't
  58  *     haveit, so we'll supply our own''
  59  *
  60  * This function is almost a literal copy of vsf_sysutil_a_to_filesize_t(),
  61  * present in that file. The only difference is that the string is processed
  62  * from left to right, in contrast with the original. Therefore, here, negative
  63  * numbers are directly converted to 0.
  64  */
  65 long long str_to_ll (char *str)
  66 {
  67         long long value = 0;
  68
  69         if (strlen(str) <= 15) {
  70                 while (*str) {
  71                         if (*str < '0' || *str > '9')
  72                                 break;
  73                         value *= 10;
  74                         value += *str - '0';
  75                         str++;
  76                 }
  77         }
  78         if (value < 0)
  79                 value = 0;
  80         return value;
  81 }
  82 #endif
  83
  84
  85 /*
  86  * path_is_secure
  87  *
  88  * Check if 'path' is trying to access beyond the Basedir. We shouldn't allow
  89  * that because we try to emulate chroot().
  90  *
  91  * This implementation is basically a small DFA (Deterministic Finite Automata)
  92  * which parses the path looking for any of the substrings "./" or "../" at the
  93  * beginning, "/./" or "/../" within, or else "/." or "/.." at the end.
  94  */
  95 int path_is_secure (char *path)
  96 {
  97         /*
  98          *       Current state ____      ____ Input value
  99          *                         \    /                       */
 100         const static int next_state[5][3] = {
 101                 /* State 0 */ { 0, 1, 4 },     /* Input values:          */
 102                 /* State 1 */ { 3, 2, 4 },     /*                        */
 103                 /* State 2 */ { 3, 4, 4 },     /*     '/' = 0            */
 104                 /* State 3 */ { 3, 3, 3 },     /*     '.' = 1            */
 105                 /* State 4 */ { 0, 4, 4 }      /*   other = 2            */
 106         };
 107         int state = 0;  /* Initial state */
 108         int input;
 109
 110         while (*path != '\0') {
 111                 switch (*path) {
 112                         case '/': input = 0; break;
 113                         case '.': input = 1; break;
 114                         default : input = 2;
 115                 }
 116                 state = next_state[state][input];
 117                 path++;
 118         }
 119
 120         /* Accepting states (safe path) are: */
 121         return state == 0 || state == 4;
 122 }
 123
 124
 125 #ifdef DEBUG
 126 /*
 127  * debug_msg
 128  *
 129  * Only implemented when debug flags are enabled. Display an information message
 130  * to the stderr. Useful to follow the progress of the command-reply exchange
 131  * without the need of a debugger.
 132  */
 133 void debug_msg (const char *format, ...)
 134 {
 135         va_list params;
 136
 137         fprintf(stderr, "(%d) ", getpid());
 138         va_start(params, format);
 139         vfprintf(stderr, format, params);
 140         va_end(params);
 141 }
 142 #endif
 143