realpath.c revision 31de2854
1/* $OpenBSD: realpath.c,v 1.14 2011/07/24 21:03:00 miod Exp $ */ 2/* 3 * Copyright (c) 2003 Constantin S. Svintsoff <kostik@iclub.nsu.ru> 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. The names of the authors may not be used to endorse or promote 14 * products derived from this software without specific prior written 15 * permission. 16 * 17 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 18 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 19 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 20 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 21 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 22 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 23 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 24 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 25 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 26 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 27 * SUCH DAMAGE. 28 */ 29 30#include <sys/param.h> 31#include <sys/stat.h> 32 33#include <errno.h> 34#include <stdlib.h> 35#include <string.h> 36#include <unistd.h> 37 38/* 39 * char *realpath(const char *path, char resolved[PATH_MAX]); 40 * 41 * Find the real name of path, by removing all ".", ".." and symlink 42 * components. Returns (resolved) on success, or (NULL) on failure, 43 * in which case the path which caused trouble is left in (resolved). 44 */ 45char * 46realpath(const char *path, char *resolved) 47{ 48 struct stat sb; 49 char *p, *q, *s; 50 size_t left_len, resolved_len; 51 unsigned symlinks; 52 int serrno, slen, mem_allocated; 53 char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX]; 54 55 if (path[0] == '\0') { 56 errno = ENOENT; 57 return (NULL); 58 } 59 60 serrno = errno; 61 62 if (resolved == NULL) { 63 resolved = malloc(PATH_MAX); 64 if (resolved == NULL) 65 return (NULL); 66 mem_allocated = 1; 67 } else 68 mem_allocated = 0; 69 70 symlinks = 0; 71 if (path[0] == '/') { 72 resolved[0] = '/'; 73 resolved[1] = '\0'; 74 if (path[1] == '\0') 75 return (resolved); 76 resolved_len = 1; 77 left_len = strlcpy(left, path + 1, sizeof(left)); 78 } else { 79 if (getcwd(resolved, PATH_MAX) == NULL) { 80 if (mem_allocated) 81 free(resolved); 82 else 83 strlcpy(resolved, ".", PATH_MAX); 84 return (NULL); 85 } 86 resolved_len = strlen(resolved); 87 left_len = strlcpy(left, path, sizeof(left)); 88 } 89 if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) { 90 errno = ENAMETOOLONG; 91 goto err; 92 } 93 94 /* 95 * Iterate over path components in `left'. 96 */ 97 while (left_len != 0) { 98 /* 99 * Extract the next path component and adjust `left' 100 * and its length. 101 */ 102 p = strchr(left, '/'); 103 s = p ? p : left + left_len; 104 if (s - left >= sizeof(next_token)) { 105 errno = ENAMETOOLONG; 106 goto err; 107 } 108 memcpy(next_token, left, s - left); 109 next_token[s - left] = '\0'; 110 left_len -= s - left; 111 if (p != NULL) 112 memmove(left, s + 1, left_len + 1); 113 if (resolved[resolved_len - 1] != '/') { 114 if (resolved_len + 1 >= PATH_MAX) { 115 errno = ENAMETOOLONG; 116 goto err; 117 } 118 resolved[resolved_len++] = '/'; 119 resolved[resolved_len] = '\0'; 120 } 121 if (next_token[0] == '\0') 122 continue; 123 else if (strcmp(next_token, ".") == 0) 124 continue; 125 else if (strcmp(next_token, "..") == 0) { 126 /* 127 * Strip the last path component except when we have 128 * single "/" 129 */ 130 if (resolved_len > 1) { 131 resolved[resolved_len - 1] = '\0'; 132 q = strrchr(resolved, '/') + 1; 133 *q = '\0'; 134 resolved_len = q - resolved; 135 } 136 continue; 137 } 138 139 /* 140 * Append the next path component and lstat() it. If 141 * lstat() fails we still can return successfully if 142 * there are no more path components left. 143 */ 144 resolved_len = strlcat(resolved, next_token, PATH_MAX); 145 if (resolved_len >= PATH_MAX) { 146 errno = ENAMETOOLONG; 147 goto err; 148 } 149 if (lstat(resolved, &sb) != 0) { 150 if (errno == ENOENT && p == NULL) { 151 errno = serrno; 152 return (resolved); 153 } 154 goto err; 155 } 156 if (S_ISLNK(sb.st_mode)) { 157 if (symlinks++ > MAXSYMLINKS) { 158 errno = ELOOP; 159 goto err; 160 } 161 slen = readlink(resolved, symlink, sizeof(symlink) - 1); 162 if (slen < 0) 163 goto err; 164 symlink[slen] = '\0'; 165 if (symlink[0] == '/') { 166 resolved[1] = 0; 167 resolved_len = 1; 168 } else if (resolved_len > 1) { 169 /* Strip the last path component. */ 170 resolved[resolved_len - 1] = '\0'; 171 q = strrchr(resolved, '/') + 1; 172 *q = '\0'; 173 resolved_len = q - resolved; 174 } 175 176 /* 177 * If there are any path components left, then 178 * append them to symlink. The result is placed 179 * in `left'. 180 */ 181 if (p != NULL) { 182 if (symlink[slen - 1] != '/') { 183 if (slen + 1 >= sizeof(symlink)) { 184 errno = ENAMETOOLONG; 185 goto err; 186 } 187 symlink[slen] = '/'; 188 symlink[slen + 1] = 0; 189 } 190 left_len = strlcat(symlink, left, sizeof(left)); 191 if (left_len >= sizeof(left)) { 192 errno = ENAMETOOLONG; 193 goto err; 194 } 195 } 196 left_len = strlcpy(left, symlink, sizeof(left)); 197 } 198 } 199 200 /* 201 * Remove trailing slash except when the resolved pathname 202 * is a single "/". 203 */ 204 if (resolved_len > 1 && resolved[resolved_len - 1] == '/') 205 resolved[resolved_len - 1] = '\0'; 206 return (resolved); 207 208err: 209 if (mem_allocated) 210 free(resolved); 211 return (NULL); 212} 213