expand_arg.c

   1 /*
   2  * User FTP Server,  Share folders over FTP without being root.
   3  * Copyright (C) 2008  Isaac Jurado
   4  *
   5  * This program is free software; you can redistribute it and/or modify it under
   6  * the terms of the GNU General Public License as published by the Free Software
   7  * Foundation; either version 2 of the License, or (at your option) any later
   8  * version.
   9  *
  10  * This program is distributed in the hope that it will be useful, but WITHOUT
  11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
  12  * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
  13  * details.
  14  *
  15  * You should have received a copy of the GNU General Public License along with
  16  * this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
  18  */
  19
  20 #include "uftps.h"
  21 #include <string.h>
  22
  23
  24 /*
  25  * Apply new path components to an existing working directory.  The working
  26  * directory is contained (full path) in "wd", which is a buffer with a capacity
  27  * of LINE_SIZE bytes.  Parameter "len" specifies the current length of the
  28  * working directory.
  29  *
  30  * This function returns the length of "wd" after applying "path" on it, which
  31  * means that the working directory is modified in-place.  In case the working
  32  * directory would exceed LINE_SIZE bytes (at any stage), -1 is returned.
  33  *
  34  * NOTE: Path lengths always include the terminating null byte.  This means that
  35  *       the last useful character of the path is at length - 2.
  36  */
  37 static int apply_path (const char *path, char *wd, int len)
  38 {
  39         int  i;
  40
  41         if (*path == '/')
  42         {
  43                 /* Absolute path, truncate wd */
  44                 wd[0] = '.';
  45                 wd[1] = '/';
  46                 wd[2] = '\0';
  47                 len   = 3;
  48         }
  49
  50         do {
  51                 /* Combine delimiters */
  52                 while (*path == '/')
  53                         path++;
  54
  55                 if (*path == '\0')
  56                         /* No more components to apply */
  57                         break;
  58
  59                 /* Isolate next component */
  60                 i = 0;
  61                 while (path[i] != '/' && path[i] != '\0')
  62                         i++;
  63
  64                 if (i == 2 && path[0] == '.' && path[1] == '.')
  65                 {
  66                         /* Return to parent directory, found ".." */
  67                         while (wd[len] != '/')
  68                                 len--;
  69                         if (len == 1)
  70                                 len++;  /* Root reached, fix */
  71                         wd[len] = '\0';
  72                         len++;
  73                 }
  74                 else if (i != 1 || path[0] != '.')
  75                 {
  76                         /* Bounds check */
  77                         if (len + i >= LINE_SIZE)
  78                                 return -1;
  79
  80                         /* Apply component, because it is different than "." */
  81                         if (len > 3)
  82                                 wd[len - 1] = '/';
  83                         else
  84                                 len--;   /* Skip delimiter at root */
  85
  86                         memcpy(wd + len, path, i);
  87                         len        += i + 1;
  88                         wd[len - 1] = '\0';
  89                 }
  90
  91                 /* Now skip to the next component */
  92                 path += i;
  93         } while (1);
  94
  95         return len;
  96 }
  97
  98
  99 /*
 100  * Expand the command argument to its corresponding full path.  This is
 101  * necessary because chdir() is never performed so the correct path needs to be
 102  * resolved for each file or directory to be accessed.
 103  *
 104  * Returns the length of the expanded argument, including the trailing null
 105  * byte (just as apply_path() does).  Also note that the expanded argument is
 106  * saved in the auxiliary buffer and the argument pointer is redirected
 107  * accordingly.
 108  */
 109 int expand_arg (void)
 110 {
 111         int  len = SS.cwd_len;
 112
 113         /* Even if the argument is empty, list_dir() requires the current
 114          * working directory to be copied */
 115         memcpy(SS.aux, SS.cwd, len);
 116
 117         if (SS.arg != NULL)
 118         {
 119                 len = apply_path(SS.arg, SS.aux, len);
 120                 if (len == -1)
 121                 {
 122                         reply_c("552 Path overflow.\r\n");
 123                         fatal("Path overflow expanding argument");
 124                 }
 125         }
 126
 127         SS.arg = SS.aux;
 128         debug("Argument expanded to %s", SS.arg);
 129         return len;
 130 }
 131