1 /*
2 * Copyright (c) 2020 Apple Inc. All rights reserved.
3 *
4 * @APPLE_LICENSE_HEADER_START@
5 *
6 * This file contains Original Code and/or Modifications of Original Code
7 * as defined in and that are subject to the Apple Public Source License
8 * Version 2.0 (the 'License'). You may not use this file except in
9 * compliance with the License. Please obtain a copy of the License at
10 * http://www.opensource.apple.com/apsl/ and read it before using this
11 * file.
12 *
13 * The Original Code and all software distributed under the License are
14 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
15 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
16 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
17 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
18 * Please see the License for the specific language governing rights and
19 * limitations under the License.
20 *
21 * @APPLE_LICENSE_HEADER_END@
22 */
23
24 #include "system-version-compat-support.h"
25
26 #if SYSTEM_VERSION_COMPAT_ENABLED
27
28
29 #include <fcntl.h>
30 #include <stdbool.h>
31 #include <strings.h>
32 #include <sys/errno.h>
33 #include <sys/param.h>
34 #include <unistd.h>
35
36 #define PLAT_PREFIX_IOS "iOS"
37 #define PLAT_PREFIX_MACOS ""
38
39 #define COMPAT_SUFFIX_MACOS "Compat"
40 #define COMPAT_SUFFIX_IOS ""
41
42 #define SYSTEM_VERSION_PLIST_FILENAME "SystemVersion.plist"
43 #define SYSTEM_VERSION_PLIST_PATH "/System/Library/CoreServices/" SYSTEM_VERSION_PLIST_FILENAME
44
45 #if TARGET_OS_OSX
46 #define SYSTEM_VERSION_PLIST_OS_CRYPTEX_PATH "/System/Volumes/Preboot/Cryptexes/OS" SYSTEM_VERSION_PLIST_PATH
47 #else
48 #define SYSTEM_VERSION_PLIST_OS_CRYPTEX_PATH "/private/preboot/Cryptexes/OS" SYSTEM_VERSION_PLIST_PATH
49 #endif /* TARGET_OS_OSX */
50
51 #define SYSTEM_VERSION_COMPAT_PLIST_FILENAME(platform_prefix, compat_suffix) (platform_prefix "SystemVersion" compat_suffix ".plist")
52
53 #define SYSTEM_VERSION_PLIST_FILENAMELEN strlen(SYSTEM_VERSION_PLIST_FILENAME)
54
55 #define SYSTEM_VERSION_COMPAT_PLIST_FILENAMELEN(platform_prefix, compat_suffix) strlen(SYSTEM_VERSION_COMPAT_PLIST_FILENAME(platform_prefix, compat_suffix))
56
57 #define SYSTEM_VERSION_PLIST_PATHLEN strlen(SYSTEM_VERSION_PLIST_PATH)
58 #define SYSTEM_VERSION_PLIST_OS_CRYPTEX_PATHLEN strlen(SYSTEM_VERSION_PLIST_OS_CRYPTEX_PATH)
59
60 extern system_version_compat_mode_t system_version_compat_mode;
61
62 /*
63 * This routine determines whether the path specified matches the path of the SystemVersion plist file
64 * we are shimming accesses to. If the file name suffix matches, it's expected we'll call into the
65 * version_compat_open_shim() routine below which will do a full comparison on the expanded path.
66 *
67 * Parameters: orig_path The path suffix that was provided to the open{at} call.
68 *
69 * Returns: true if the path suffix matches the SystemVersion plist path we're shimming
70 * false otherwise
71 */
72 __attribute__((visibility("hidden")))
73 bool
_system_version_compat_check_path_suffix(const char * orig_path)74 _system_version_compat_check_path_suffix(const char *orig_path)
75 {
76 size_t path_str_len = strnlen(orig_path, MAXPATHLEN);
77 /*
78 * If the length of the filename we're opening is shorter than
79 * SYSTEM_VERSION_PLIST_FILENAME, bail.
80 */
81 if (path_str_len < SYSTEM_VERSION_PLIST_FILENAMELEN) {
82 return false;
83 }
84
85 /* If the path we're accessing doesn't end in SYSTEM_VERSION_PLIST_FILENAME, bail. */
86 if (strncmp(&orig_path[path_str_len - SYSTEM_VERSION_PLIST_FILENAMELEN], SYSTEM_VERSION_PLIST_FILENAME,
87 SYSTEM_VERSION_PLIST_FILENAMELEN) != 0) {
88 return false;
89 }
90
91 /* If modifying the path specified would exceed MAXPATHLEN, bail */
92 if (path_str_len == MAXPATHLEN) {
93 return false;
94 }
95
96 size_t compat_len = (system_version_compat_mode == SYSTEM_VERSION_COMPAT_MODE_IOS) ? SYSTEM_VERSION_COMPAT_PLIST_FILENAMELEN(PLAT_PREFIX_IOS, COMPAT_SUFFIX_IOS) : SYSTEM_VERSION_COMPAT_PLIST_FILENAMELEN(PLAT_PREFIX_MACOS, COMPAT_SUFFIX_MACOS);
97 if ((compat_len - SYSTEM_VERSION_PLIST_FILENAMELEN) > (MAXPATHLEN - path_str_len - 1)) {
98 return false;
99 }
100
101 /* Indicate that we should */
102 return true;
103 }
104
105 /*
106 * This routine determines whether we are trying to open the SystemVersion plist at SYSTEM_VERSION_PLIST_PATH.
107 * It's only used on targets that have the compatibility shim enabled (mainly older binaries).
108 *
109 * Note that this routine should * ABSOLUTELY NOT * be used as a general shim for accesses at all paths. We replace
110 * what the developer generally expected to be one system call with multiple additional system calls. We're ok
111 * with doing this here because we only do it for calls to open against files that match this very specific pattern
112 * (named SystemVersion.plist), but doing so for all calls to open could result in various issues. Specifically it's
113 * difficult to ensure the same cancellation semantics (around EINTR etc) that developers generally expect when replacing
114 * a single system call with multiple.
115 *
116 * This routine should return with the same semantics as the general open system calls that it is shimming - specifically
117 * it should leave errno and the return value matching what developers expect.
118 *
119 * It's expected that _version_compat_check_path_suffix() above was called prior to this call and returned true.
120 *
121 * We take the close, open and fcntl syscalls as parameters to make sure the variant we call matches the original call
122 * to open{at}.
123 *
124 * Parameters: opened_fd The file descriptor that was opened in the original open{at} call
125 * openat_fd The file descriptor passed to the original openat call (only used when use_openat is true)
126 * orig_path The original path suffix passed to open{at}
127 * oflag The original oflag passed to open{at}
128 * mode The original mode passed to open{at}
129 * close_syscall The appropriate syscall to use for closing file descriptors
130 * open_syscall The syscall that should be used for a new call to open.
131 * fctnl_syscall The appopriate syscall to use for fcntl.
132 *
133 * Returns: The original file descriptor if the open{at} access wasn't to SYSTEM_VERSION_PLIST_PATH
134 * A new file descriptor (with the original closed) if the expanded path matches SYSTEM_VERSION_PLIST_PATH
135 * The original file descriptor if the full path suffix does not match SYSTEM_VERSION_PLIST_PATH
136 * -1 (with errno set to EINTR) if the new open or fcntl calls received EINTR (with all new fds closed)
137 */
138 __attribute__((visibility("hidden")))
139 int
_system_version_compat_open_shim(int opened_fd,int openat_fd,const char * orig_path,int oflag,mode_t mode,int (* close_syscall)(int),int (* open_syscall)(const char *,int,mode_t),int (* openat_syscall)(int,const char *,int,mode_t),int (* fcntl_syscall)(int,int,long))140 _system_version_compat_open_shim(int opened_fd, int openat_fd, const char *orig_path, int oflag, mode_t mode,
141 int (*close_syscall)(int), int (*open_syscall)(const char *, int, mode_t),
142 int (*openat_syscall)(int, const char *, int, mode_t),
143 int (*fcntl_syscall)(int, int, long))
144 {
145 /* stash the errno from the original open{at} call */
146 int stashed_errno = errno;
147 char new_path[MAXPATHLEN];
148 size_t path_str_len = strnlen(orig_path, sizeof(new_path));
149
150 /* Resolve the full path of the file we've opened */
151 if (fcntl_syscall(opened_fd, F_GETPATH, new_path)) {
152 if (errno == EINTR) {
153 /* If we got EINTR, we close the file that was opened and return -1 & EINTR */
154 close_syscall(opened_fd);
155 errno = EINTR;
156 return -1;
157 } else {
158 /* otherwise we return the original file descriptor that was requested */
159 errno = stashed_errno;
160 return opened_fd;
161 }
162 }
163
164 bool path_needs_shim = false;
165 size_t newpathlen = strnlen(new_path, MAXPATHLEN);
166
167 /* Check to see whether the path matches SYSTEM_VERSION_PLIST_PATH */
168 if (newpathlen == SYSTEM_VERSION_PLIST_PATHLEN &&
169 strncmp(new_path, SYSTEM_VERSION_PLIST_PATH, newpathlen) == 0) {
170 path_needs_shim = true;
171 }
172
173 #if SYSTEM_VERSION_COMPAT_SHIM_OS_CRYPTEX
174 /* Check to see whether the path matches SYSTEM_VERSION_PLIST_OS_CRYPTEX_PATH */
175 if (newpathlen == SYSTEM_VERSION_PLIST_OS_CRYPTEX_PATHLEN &&
176 strncmp(new_path, SYSTEM_VERSION_PLIST_OS_CRYPTEX_PATH, newpathlen) == 0) {
177 path_needs_shim = true;
178
179 /* Redirect to the system volume path */
180 orig_path = SYSTEM_VERSION_PLIST_PATH;
181 path_str_len = SYSTEM_VERSION_PLIST_PATHLEN;
182 }
183 #endif /* SYSTEM_VERSION_COMPAT_SHIM_OS_CRYPTEX */
184
185 if (!path_needs_shim) {
186 errno = stashed_errno;
187 return opened_fd;
188 }
189
190 new_path[0] = '\0';
191
192 /*
193 * It looks like we're trying to access the SystemVersion plist. Let's try to open
194 * the compatibility plist and return that instead if it exists.
195 */
196 size_t prefix_str_len = path_str_len - SYSTEM_VERSION_PLIST_FILENAMELEN;
197 strlcpy(new_path, orig_path, (prefix_str_len + 1));
198 if (system_version_compat_mode == SYSTEM_VERSION_COMPAT_MODE_IOS) {
199 strlcat(new_path, SYSTEM_VERSION_COMPAT_PLIST_FILENAME(PLAT_PREFIX_IOS, COMPAT_SUFFIX_IOS), MAXPATHLEN);
200 } else {
201 strlcat(new_path, SYSTEM_VERSION_COMPAT_PLIST_FILENAME(PLAT_PREFIX_MACOS, COMPAT_SUFFIX_MACOS), MAXPATHLEN);
202 }
203
204 int new_fd = -1;
205 if (openat_syscall != NULL) {
206 new_fd = openat_syscall(openat_fd, new_path, oflag, mode);
207 } else {
208 new_fd = open_syscall(new_path, oflag, mode);
209 }
210 if ((new_fd == -1) && (errno == ENOENT)) {
211 /* The file doesn't exist, so return the original fd and errno. */
212 errno = stashed_errno;
213 return opened_fd;
214 }
215
216 /*
217 * Otherwise we close the first file we opened and populate errno
218 * with errno from the call to open{at}. (Note this covers the EINTR
219 * case and other failures).
220 */
221 stashed_errno = errno;
222 close_syscall(opened_fd);
223 errno = stashed_errno;
224 return new_fd;
225 }
226
227 #endif /* SYSTEM_VERSION_COMPAT_ENABLED */
228