src/lib/encoding/cstring.c

   1 /* Copyright (c) 2001 Matej Pfajfar.
   2  * Copyright (c) 2001-2004, Roger Dingledine.
   3  * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
   4  * Copyright (c) 2007-2021, The Tor Project, Inc. */
   5 /* See LICENSE for licensing information */
   6
   7 /**
   8  * \file cstring.c
   9  *
  10  * \brief Decode data that has been written as a C literal.
  11  **/
  12
  13 #include "lib/encoding/cstring.h"
  14 #include "lib/log/log.h"
  15 #include "lib/log/util_bug.h"
  16 #include "lib/malloc/malloc.h"
  17 #include "lib/string/compat_ctype.h"
  18
  19 #include <string.h>
  20
  21 #define TOR_ISODIGIT(c) ('0' <= (c) && (c) <= '7')
  22
  23 /** Given a c-style double-quoted escaped string in <b>s</b>, extract and
  24  * decode its contents into a newly allocated string.  On success, assign this
  25  * string to *<b>result</b>, assign its length to <b>size_out</b> (if
  26  * provided), and return a pointer to the position in <b>s</b> immediately
  27  * after the string.  On failure, return NULL.
  28  */
  29 const char *
  30 unescape_string(const char *s, char **result, size_t *size_out)
  31 {
  32   const char *cp;
  33   char *out;
  34   if (s[0] != '\"')
  35     return NULL;
  36   cp = s+1;
  37   while (1) {
  38     switch (*cp) {
  39       case '\0':
  40       case '\n':
  41         return NULL;
  42       case '\"':
  43         goto end_of_loop;
  44       case '\\':
  45         if (cp[1] == 'x' || cp[1] == 'X') {
  46           if (!(TOR_ISXDIGIT(cp[2]) && TOR_ISXDIGIT(cp[3])))
  47             return NULL;
  48           cp += 4;
  49         } else if (TOR_ISODIGIT(cp[1])) {
  50           cp += 2;
  51           if (TOR_ISODIGIT(*cp)) ++cp;
  52           if (TOR_ISODIGIT(*cp)) ++cp;
  53         } else if (cp[1] == 'n' || cp[1] == 'r' || cp[1] == 't' || cp[1] == '"'
  54                    || cp[1] == '\\' || cp[1] == '\'') {
  55           cp += 2;
  56         } else {
  57           return NULL;
  58         }
  59         break;
  60       default:
  61         ++cp;
  62         break;
  63     }
  64   }
  65  end_of_loop:
  66   out = *result = tor_malloc(cp-s + 1);
  67   cp = s+1;
  68   while (1) {
  69     switch (*cp)
  70       {
  71       case '\"':
  72         *out = '\0';
  73         if (size_out) *size_out = out - *result;
  74         return cp+1;
  75
  76         /* LCOV_EXCL_START -- we caught this in parse_config_from_line. */
  77       case '\0':
  78         tor_fragile_assert();
  79         tor_free(*result);
  80         return NULL;
  81         /* LCOV_EXCL_STOP */
  82       case '\\':
  83         switch (cp[1])
  84           {
  85           case 'n': *out++ = '\n'; cp += 2; break;
  86           case 'r': *out++ = '\r'; cp += 2; break;
  87           case 't': *out++ = '\t'; cp += 2; break;
  88           case 'x': case 'X':
  89             {
  90               int x1, x2;
  91
  92               x1 = hex_decode_digit(cp[2]);
  93               x2 = hex_decode_digit(cp[3]);
  94               if (x1 == -1 || x2 == -1) {
  95                 /* LCOV_EXCL_START */
  96                 /* we caught this above in the initial loop. */
  97                 tor_assert_nonfatal_unreached();
  98                 tor_free(*result);
  99                 return NULL;
 100                 /* LCOV_EXCL_STOP */
 101               }
 102
 103               *out++ = ((x1<<4) + x2);
 104               cp += 4;
 105             }
 106             break;
 107           case '0': case '1': case '2': case '3': case '4': case '5':
 108           case '6': case '7':
 109             {
 110               int n = cp[1]-'0';
 111               cp += 2;
 112               if (TOR_ISODIGIT(*cp)) { n = n*8 + *cp-'0'; cp++; }
 113               if (TOR_ISODIGIT(*cp)) { n = n*8 + *cp-'0'; cp++; }
 114               if (n > 255) { tor_free(*result); return NULL; }
 115               *out++ = (char)n;
 116             }
 117             break;
 118           case '\'':
 119           case '\"':
 120           case '\\':
 121           case '\?':
 122             *out++ = cp[1];
 123             cp += 2;
 124             break;
 125
 126             /* LCOV_EXCL_START */
 127           default:
 128             /* we caught this above in the initial loop. */
 129             tor_assert_nonfatal_unreached();
 130             tor_free(*result); return NULL;
 131             /* LCOV_EXCL_STOP */
 132           }
 133         break;
 134       default:
 135         *out++ = *cp++;
 136       }
 137   }
 138 }