1 /* $OpenBSD: sftp-realpath.c,v 1.2 2021/09/02 21:03:54 deraadt 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/types.h> 31 #include <sys/stat.h> 32 33 #include <errno.h> 34 #include <stdlib.h> 35 #include <stddef.h> 36 #include <string.h> 37 #include <unistd.h> 38 #include <limits.h> 39 40 #ifndef SYMLOOP_MAX 41 # define SYMLOOP_MAX 32 42 #endif 43 44 /* XXX rewrite sftp-server to use POSIX realpath and remove this hack */ 45 46 char *sftp_realpath(const char *path, char *resolved); 47 48 /* 49 * char *realpath(const char *path, char resolved[PATH_MAX]); 50 * 51 * Find the real name of path, by removing all ".", ".." and symlink 52 * components. Returns (resolved) on success, or (NULL) on failure, 53 * in which case the path which caused trouble is left in (resolved). 54 */ 55 char * 56 sftp_realpath(const char *path, char *resolved) 57 { 58 struct stat sb; 59 char *p, *q, *s; 60 size_t left_len, resolved_len; 61 unsigned symlinks; 62 int serrno, slen, mem_allocated; 63 char left[PATH_MAX], next_token[PATH_MAX], symlink[PATH_MAX]; 64 65 if (path[0] == '\0') { 66 errno = ENOENT; 67 return (NULL); 68 } 69 70 serrno = errno; 71 72 if (resolved == NULL) { 73 resolved = malloc(PATH_MAX); 74 if (resolved == NULL) 75 return (NULL); 76 mem_allocated = 1; 77 } else 78 mem_allocated = 0; 79 80 symlinks = 0; 81 if (path[0] == '/') { 82 resolved[0] = '/'; 83 resolved[1] = '\0'; 84 if (path[1] == '\0') 85 return (resolved); 86 resolved_len = 1; 87 left_len = strlcpy(left, path + 1, sizeof(left)); 88 } else { 89 if (getcwd(resolved, PATH_MAX) == NULL) { 90 if (mem_allocated) 91 free(resolved); 92 else 93 strlcpy(resolved, ".", PATH_MAX); 94 return (NULL); 95 } 96 resolved_len = strlen(resolved); 97 left_len = strlcpy(left, path, sizeof(left)); 98 } 99 if (left_len >= sizeof(left) || resolved_len >= PATH_MAX) { 100 errno = ENAMETOOLONG; 101 goto err; 102 } 103 104 /* 105 * Iterate over path components in `left'. 106 */ 107 while (left_len != 0) { 108 /* 109 * Extract the next path component and adjust `left' 110 * and its length. 111 */ 112 p = strchr(left, '/'); 113 s = p ? p : left + left_len; 114 if (s - left >= (ptrdiff_t)sizeof(next_token)) { 115 errno = ENAMETOOLONG; 116 goto err; 117 } 118 memcpy(next_token, left, s - left); 119 next_token[s - left] = '\0'; 120 left_len -= s - left; 121 if (p != NULL) 122 memmove(left, s + 1, left_len + 1); 123 if (resolved[resolved_len - 1] != '/') { 124 if (resolved_len + 1 >= PATH_MAX) { 125 errno = ENAMETOOLONG; 126 goto err; 127 } 128 resolved[resolved_len++] = '/'; 129 resolved[resolved_len] = '\0'; 130 } 131 if (next_token[0] == '\0') 132 continue; 133 else if (strcmp(next_token, ".") == 0) 134 continue; 135 else if (strcmp(next_token, "..") == 0) { 136 /* 137 * Strip the last path component except when we have 138 * single "/" 139 */ 140 if (resolved_len > 1) { 141 resolved[resolved_len - 1] = '\0'; 142 q = strrchr(resolved, '/') + 1; 143 *q = '\0'; 144 resolved_len = q - resolved; 145 } 146 continue; 147 } 148 149 /* 150 * Append the next path component and lstat() it. If 151 * lstat() fails we still can return successfully if 152 * there are no more path components left. 153 */ 154 resolved_len = strlcat(resolved, next_token, PATH_MAX); 155 if (resolved_len >= PATH_MAX) { 156 errno = ENAMETOOLONG; 157 goto err; 158 } 159 if (lstat(resolved, &sb) != 0) { 160 if (errno == ENOENT && p == NULL) { 161 errno = serrno; 162 return (resolved); 163 } 164 goto err; 165 } 166 if (S_ISLNK(sb.st_mode)) { 167 if (symlinks++ > SYMLOOP_MAX) { 168 errno = ELOOP; 169 goto err; 170 } 171 slen = readlink(resolved, symlink, sizeof(symlink) - 1); 172 if (slen < 0) 173 goto err; 174 symlink[slen] = '\0'; 175 if (symlink[0] == '/') { 176 resolved[1] = 0; 177 resolved_len = 1; 178 } else if (resolved_len > 1) { 179 /* Strip the last path component. */ 180 resolved[resolved_len - 1] = '\0'; 181 q = strrchr(resolved, '/') + 1; 182 *q = '\0'; 183 resolved_len = q - resolved; 184 } 185 186 /* 187 * If there are any path components left, then 188 * append them to symlink. The result is placed 189 * in `left'. 190 */ 191 if (p != NULL) { 192 if (symlink[slen - 1] != '/') { 193 if (slen + 1 >= 194 (ptrdiff_t)sizeof(symlink)) { 195 errno = ENAMETOOLONG; 196 goto err; 197 } 198 symlink[slen] = '/'; 199 symlink[slen + 1] = 0; 200 } 201 left_len = strlcat(symlink, left, sizeof(symlink)); 202 if (left_len >= sizeof(symlink)) { 203 errno = ENAMETOOLONG; 204 goto err; 205 } 206 } 207 left_len = strlcpy(left, symlink, sizeof(left)); 208 } 209 } 210 211 /* 212 * Remove trailing slash except when the resolved pathname 213 * is a single "/". 214 */ 215 if (resolved_len > 1 && resolved[resolved_len - 1] == '/') 216 resolved[resolved_len - 1] = '\0'; 217 return (resolved); 218 219 err: 220 if (mem_allocated) 221 free(resolved); 222 return (NULL); 223 } 224