1 #include <sys/types.h>
2 #include <sys/stat.h>
3 #include <fcntl.h>
4 #include <sys/ioctl.h>
5
6 #include <string>
7
8 #include "capsicum.h"
9 #include "capsicum-test.h"
10 #include "syscalls.h"
11
12 // Check an open call works and close the resulting fd.
13 #define EXPECT_OPEN_OK(f) do { \
14 SCOPED_TRACE(#f); \
15 int _fd = f; \
16 EXPECT_OK(_fd); \
17 close(_fd); \
18 } while (0)
19
CreateFile(const char * filename,const char * contents)20 static void CreateFile(const char *filename, const char *contents) {
21 int fd = open(filename, O_CREAT|O_RDWR, 0644);
22 EXPECT_OK(fd);
23 EXPECT_OK(write(fd, contents, strlen(contents)));
24 close(fd);
25 }
26
27 // Test openat(2) in a variety of sitations to ensure that it obeys Capsicum
28 // "strict relative" rules:
29 //
30 // 1. Use strict relative lookups in capability mode or when operating
31 // relative to a capability.
32 // 2. When performing strict relative lookups, absolute paths (including
33 // symlinks to absolute paths) are not allowed, nor are paths containing
34 // '..' components.
35 //
36 // These rules apply when:
37 // - the directory FD is a Capsicum capability
38 // - the process is in capability mode
39 // - the openat(2) operation includes the O_BENEATH flag.
FORK_TEST(Openat,Relative)40 FORK_TEST(Openat, Relative) {
41 int etc = open("/etc/", O_RDONLY);
42 EXPECT_OK(etc);
43
44 cap_rights_t r_base;
45 cap_rights_init(&r_base, CAP_READ, CAP_WRITE, CAP_SEEK, CAP_LOOKUP, CAP_FCNTL, CAP_IOCTL);
46 cap_rights_t r_ro;
47 cap_rights_init(&r_ro, CAP_READ);
48 cap_rights_t r_rl;
49 cap_rights_init(&r_rl, CAP_READ, CAP_LOOKUP);
50
51 int etc_cap = dup(etc);
52 EXPECT_OK(etc_cap);
53 EXPECT_OK(cap_rights_limit(etc_cap, &r_ro));
54 int etc_cap_ro = dup(etc);
55 EXPECT_OK(etc_cap_ro);
56 EXPECT_OK(cap_rights_limit(etc_cap_ro, &r_rl));
57 int etc_cap_base = dup(etc);
58 EXPECT_OK(etc_cap_base);
59 EXPECT_OK(cap_rights_limit(etc_cap_base, &r_base));
60 #ifdef HAVE_CAP_FCNTLS_LIMIT
61 // Also limit fcntl(2) subrights.
62 EXPECT_OK(cap_fcntls_limit(etc_cap_base, CAP_FCNTL_GETFL));
63 #endif
64 #ifdef HAVE_CAP_IOCTLS_LIMIT
65 // Also limit ioctl(2) subrights.
66 cap_ioctl_t ioctl_nread = FIONREAD;
67 EXPECT_OK(cap_ioctls_limit(etc_cap_base, &ioctl_nread, 1));
68 #endif
69
70 // openat(2) with regular file descriptors in non-capability mode
71 // Should Just Work (tm).
72 EXPECT_OPEN_OK(openat(etc, "/etc/passwd", O_RDONLY));
73 EXPECT_OPEN_OK(openat(AT_FDCWD, "/etc/passwd", O_RDONLY));
74 EXPECT_OPEN_OK(openat(etc, "passwd", O_RDONLY));
75 EXPECT_OPEN_OK(openat(etc, "../etc/passwd", O_RDONLY));
76
77 // Lookups relative to capabilities should be strictly relative.
78 // When not in capability mode, we don't actually require CAP_LOOKUP.
79 EXPECT_OPEN_OK(openat(etc_cap_ro, "passwd", O_RDONLY));
80 EXPECT_OPEN_OK(openat(etc_cap_base, "passwd", O_RDONLY));
81
82 // Performing openat(2) on a path with leading slash ignores
83 // the provided directory FD.
84 EXPECT_OPEN_OK(openat(etc_cap_ro, "/etc/passwd", O_RDONLY));
85 EXPECT_OPEN_OK(openat(etc_cap_base, "/etc/passwd", O_RDONLY));
86 // Relative lookups that go upward are not allowed.
87 EXPECT_OPENAT_FAIL_TRAVERSAL(etc_cap_ro, "../etc/passwd", O_RDONLY);
88 EXPECT_OPENAT_FAIL_TRAVERSAL(etc_cap_base, "../etc/passwd", O_RDONLY);
89
90 // A file opened relative to a capability should itself be a capability.
91 int fd = openat(etc_cap_base, "passwd", O_RDONLY);
92 EXPECT_OK(fd);
93 cap_rights_t rights;
94 EXPECT_OK(cap_rights_get(fd, &rights));
95 EXPECT_RIGHTS_IN(&rights, &r_base);
96 #ifdef HAVE_CAP_FCNTLS_LIMIT
97 cap_fcntl_t fcntls;
98 EXPECT_OK(cap_fcntls_get(fd, &fcntls));
99 EXPECT_EQ((cap_fcntl_t)CAP_FCNTL_GETFL, fcntls);
100 #endif
101 #ifdef HAVE_CAP_IOCTLS_LIMIT
102 cap_ioctl_t ioctls[16];
103 ssize_t nioctls;
104 memset(ioctls, 0, sizeof(ioctls));
105 nioctls = cap_ioctls_get(fd, ioctls, 16);
106 EXPECT_OK(nioctls);
107 EXPECT_EQ(1, nioctls);
108 EXPECT_EQ((cap_ioctl_t)FIONREAD, ioctls[0]);
109 #endif
110 close(fd);
111
112 // Enter capability mode; now ALL lookups are strictly relative.
113 EXPECT_OK(cap_enter());
114
115 // Relative lookups on regular files or capabilities with CAP_LOOKUP
116 // ought to succeed.
117 EXPECT_OPEN_OK(openat(etc, "passwd", O_RDONLY));
118 EXPECT_OPEN_OK(openat(etc_cap_ro, "passwd", O_RDONLY));
119 EXPECT_OPEN_OK(openat(etc_cap_base, "passwd", O_RDONLY));
120
121 // Lookup relative to capabilities without CAP_LOOKUP should fail.
122 EXPECT_NOTCAPABLE(openat(etc_cap, "passwd", O_RDONLY));
123
124 // Absolute lookups should fail.
125 EXPECT_CAPMODE(openat(AT_FDCWD, "/etc/passwd", O_RDONLY));
126 EXPECT_OPENAT_FAIL_TRAVERSAL(etc, "/etc/passwd", O_RDONLY);
127 EXPECT_OPENAT_FAIL_TRAVERSAL(etc_cap_ro, "/etc/passwd", O_RDONLY);
128
129 // Lookups containing '..' should fail in capability mode.
130 EXPECT_OPENAT_FAIL_TRAVERSAL(etc, "../etc/passwd", O_RDONLY);
131 EXPECT_OPENAT_FAIL_TRAVERSAL(etc_cap_ro, "../etc/passwd", O_RDONLY);
132 EXPECT_OPENAT_FAIL_TRAVERSAL(etc_cap_base, "../etc/passwd", O_RDONLY);
133
134 fd = openat(etc, "passwd", O_RDONLY);
135 EXPECT_OK(fd);
136
137 // A file opened relative to a capability should itself be a capability.
138 fd = openat(etc_cap_base, "passwd", O_RDONLY);
139 EXPECT_OK(fd);
140 EXPECT_OK(cap_rights_get(fd, &rights));
141 EXPECT_RIGHTS_IN(&rights, &r_base);
142 close(fd);
143
144 fd = openat(etc_cap_ro, "passwd", O_RDONLY);
145 EXPECT_OK(fd);
146 EXPECT_OK(cap_rights_get(fd, &rights));
147 EXPECT_RIGHTS_IN(&rights, &r_rl);
148 close(fd);
149 }
150
151 #define TOPDIR "cap_topdir"
152 #define SUBDIR TOPDIR "/subdir"
153 class OpenatTest : public ::testing::Test {
154 public:
155 // Build a collection of files, subdirs and symlinks:
156 // /tmp/cap_topdir/
157 // /topfile
158 // /subdir/
159 // /subdir/bottomfile
160 // /symlink.samedir -> topfile
161 // /dsymlink.samedir -> ./
162 // /symlink.down -> subdir/bottomfile
163 // /dsymlink.down -> subdir/
164 // /symlink.absolute_out -> /etc/passwd
165 // /dsymlink.absolute_out -> /etc/
166 // /symlink.relative_in -> ../../tmp/cap_topdir/topfile
167 // /dsymlink.relative_in -> ../../tmp/cap_topdir/
168 // /symlink.relative_out -> ../../etc/passwd
169 // /dsymlink.relative_out -> ../../etc/
170 // /subdir/dsymlink.absolute_in -> /tmp/cap_topdir/
171 // /subdir/dsymlink.up -> ../
172 // /subdir/symlink.absolute_in -> /tmp/cap_topdir/topfile
173 // /subdir/symlink.up -> ../topfile
174 // (In practice, this is a little more complicated because tmpdir might
175 // not be "/tmp".)
OpenatTest()176 OpenatTest() {
177 // Create a couple of nested directories
178 int rc = mkdir(TmpFile(TOPDIR), 0755);
179 EXPECT_OK(rc);
180 if (rc < 0) {
181 EXPECT_EQ(EEXIST, errno);
182 }
183 rc = mkdir(TmpFile(SUBDIR), 0755);
184 EXPECT_OK(rc);
185 if (rc < 0) {
186 EXPECT_EQ(EEXIST, errno);
187 }
188
189 // Figure out a path prefix (like "../..") that gets us to the root
190 // directory from TmpFile(TOPDIR).
191 const char *p = TmpFile(TOPDIR); // maybe "/tmp/somewhere/cap_topdir"
192 std::string dots2root = "..";
193 while (*p++ != '\0') {
194 if (*p == '/') {
195 dots2root += "/..";
196 }
197 }
198
199 // Create normal files in each.
200 CreateFile(TmpFile(TOPDIR "/topfile"), "Top-level file");
201 CreateFile(TmpFile(SUBDIR "/bottomfile"), "File in subdirectory");
202
203 // Create various symlinks to files.
204 EXPECT_OK(symlink("topfile", TmpFile(TOPDIR "/symlink.samedir")));
205 EXPECT_OK(symlink("subdir/bottomfile", TmpFile(TOPDIR "/symlink.down")));
206 EXPECT_OK(symlink(TmpFile(TOPDIR "/topfile"), TmpFile(SUBDIR "/symlink.absolute_in")));
207 EXPECT_OK(symlink("/etc/passwd", TmpFile(TOPDIR "/symlink.absolute_out")));
208 std::string dots2top = dots2root + TmpFile(TOPDIR "/topfile");
209 EXPECT_OK(symlink(dots2top.c_str(), TmpFile(TOPDIR "/symlink.relative_in")));
210 std::string dots2passwd = dots2root + "/etc/passwd";
211 EXPECT_OK(symlink(dots2passwd.c_str(), TmpFile(TOPDIR "/symlink.relative_out")));
212 EXPECT_OK(symlink("../topfile", TmpFile(SUBDIR "/symlink.up")));
213
214 // Create various symlinks to directories.
215 EXPECT_OK(symlink("./", TmpFile(TOPDIR "/dsymlink.samedir")));
216 EXPECT_OK(symlink("subdir/", TmpFile(TOPDIR "/dsymlink.down")));
217 EXPECT_OK(symlink(TmpFile(TOPDIR "/"), TmpFile(SUBDIR "/dsymlink.absolute_in")));
218 EXPECT_OK(symlink("/etc/", TmpFile(TOPDIR "/dsymlink.absolute_out")));
219 std::string dots2cwd = dots2root + tmpdir + "/";
220 EXPECT_OK(symlink(dots2cwd.c_str(), TmpFile(TOPDIR "/dsymlink.relative_in")));
221 std::string dots2etc = dots2root + "/etc/";
222 EXPECT_OK(symlink(dots2etc.c_str(), TmpFile(TOPDIR "/dsymlink.relative_out")));
223 EXPECT_OK(symlink("../", TmpFile(SUBDIR "/dsymlink.up")));
224
225 // Open directory FDs for those directories and for cwd.
226 dir_fd_ = open(TmpFile(TOPDIR), O_RDONLY);
227 EXPECT_OK(dir_fd_);
228 sub_fd_ = open(TmpFile(SUBDIR), O_RDONLY);
229 EXPECT_OK(sub_fd_);
230 cwd_ = openat(AT_FDCWD, ".", O_RDONLY);
231 EXPECT_OK(cwd_);
232 // Move into the directory for the test.
233 EXPECT_OK(fchdir(dir_fd_));
234 }
~OpenatTest()235 ~OpenatTest() {
236 fchdir(cwd_);
237 close(cwd_);
238 close(sub_fd_);
239 close(dir_fd_);
240 unlink(TmpFile(SUBDIR "/symlink.up"));
241 unlink(TmpFile(SUBDIR "/symlink.absolute_in"));
242 unlink(TmpFile(TOPDIR "/symlink.absolute_out"));
243 unlink(TmpFile(TOPDIR "/symlink.relative_in"));
244 unlink(TmpFile(TOPDIR "/symlink.relative_out"));
245 unlink(TmpFile(TOPDIR "/symlink.down"));
246 unlink(TmpFile(TOPDIR "/symlink.samedir"));
247 unlink(TmpFile(SUBDIR "/dsymlink.up"));
248 unlink(TmpFile(SUBDIR "/dsymlink.absolute_in"));
249 unlink(TmpFile(TOPDIR "/dsymlink.absolute_out"));
250 unlink(TmpFile(TOPDIR "/dsymlink.relative_in"));
251 unlink(TmpFile(TOPDIR "/dsymlink.relative_out"));
252 unlink(TmpFile(TOPDIR "/dsymlink.down"));
253 unlink(TmpFile(TOPDIR "/dsymlink.samedir"));
254 unlink(TmpFile(SUBDIR "/bottomfile"));
255 unlink(TmpFile(TOPDIR "/topfile"));
256 rmdir(TmpFile(SUBDIR));
257 rmdir(TmpFile(TOPDIR));
258 }
259
260 // Check openat(2) policing that is common across capabilities, capability mode and O_BENEATH.
CheckPolicing(int oflag)261 void CheckPolicing(int oflag) {
262 // OK for normal access.
263 EXPECT_OPEN_OK(openat(dir_fd_, "topfile", O_RDONLY|oflag));
264 EXPECT_OPEN_OK(openat(dir_fd_, "subdir/bottomfile", O_RDONLY|oflag));
265 EXPECT_OPEN_OK(openat(sub_fd_, "bottomfile", O_RDONLY|oflag));
266 EXPECT_OPEN_OK(openat(sub_fd_, ".", O_RDONLY|oflag));
267
268 // Can't open paths with ".." in them.
269 EXPECT_OPENAT_FAIL_TRAVERSAL(sub_fd_, "../topfile", O_RDONLY|oflag);
270 EXPECT_OPENAT_FAIL_TRAVERSAL(sub_fd_, "../subdir/bottomfile", O_RDONLY|oflag);
271 EXPECT_OPENAT_FAIL_TRAVERSAL(sub_fd_, "..", O_RDONLY|oflag);
272
273 #ifdef HAVE_OPENAT_INTERMEDIATE_DOTDOT
274 // OK for dotdot lookups that don't escape the top directory
275 EXPECT_OPEN_OK(openat(dir_fd_, "subdir/../topfile", O_RDONLY|oflag));
276 #endif
277
278 // Check that we can't escape the top directory by the cunning
279 // ruse of going via a subdirectory.
280 EXPECT_OPENAT_FAIL_TRAVERSAL(dir_fd_, "subdir/../../etc/passwd", O_RDONLY|oflag);
281
282 // Should only be able to open symlinks that stay within the directory.
283 EXPECT_OPEN_OK(openat(dir_fd_, "symlink.samedir", O_RDONLY|oflag));
284 EXPECT_OPEN_OK(openat(dir_fd_, "symlink.down", O_RDONLY|oflag));
285 EXPECT_OPENAT_FAIL_TRAVERSAL(dir_fd_, "symlink.absolute_out", O_RDONLY|oflag);
286 EXPECT_OPENAT_FAIL_TRAVERSAL(dir_fd_, "symlink.relative_in", O_RDONLY|oflag);
287 EXPECT_OPENAT_FAIL_TRAVERSAL(dir_fd_, "symlink.relative_out", O_RDONLY|oflag);
288 EXPECT_OPENAT_FAIL_TRAVERSAL(sub_fd_, "symlink.absolute_in", O_RDONLY|oflag);
289 EXPECT_OPENAT_FAIL_TRAVERSAL(sub_fd_, "symlink.up", O_RDONLY|oflag);
290
291 EXPECT_OPEN_OK(openat(dir_fd_, "dsymlink.samedir/topfile", O_RDONLY|oflag));
292 EXPECT_OPEN_OK(openat(dir_fd_, "dsymlink.down/bottomfile", O_RDONLY|oflag));
293 EXPECT_OPENAT_FAIL_TRAVERSAL(dir_fd_, "dsymlink.absolute_out/passwd", O_RDONLY|oflag);
294 EXPECT_OPENAT_FAIL_TRAVERSAL(dir_fd_, "dsymlink.relative_in/topfile", O_RDONLY|oflag);
295 EXPECT_OPENAT_FAIL_TRAVERSAL(dir_fd_, "dsymlink.relative_out/passwd", O_RDONLY|oflag);
296 EXPECT_OPENAT_FAIL_TRAVERSAL(sub_fd_, "dsymlink.absolute_in/topfile", O_RDONLY|oflag);
297 EXPECT_OPENAT_FAIL_TRAVERSAL(sub_fd_, "dsymlink.up/topfile", O_RDONLY|oflag);
298
299 // Although recall that O_NOFOLLOW prevents symlink following in final component.
300 EXPECT_SYSCALL_FAIL(E_TOO_MANY_LINKS, openat(dir_fd_, "symlink.samedir", O_RDONLY|O_NOFOLLOW|oflag));
301 EXPECT_SYSCALL_FAIL(E_TOO_MANY_LINKS, openat(dir_fd_, "symlink.down", O_RDONLY|O_NOFOLLOW|oflag));
302 }
303
304 protected:
305 int dir_fd_;
306 int sub_fd_;
307 int cwd_;
308 };
309
TEST_F(OpenatTest,WithCapability)310 TEST_F(OpenatTest, WithCapability) {
311 // Any kind of symlink can be opened relative to an ordinary directory FD.
312 EXPECT_OPEN_OK(openat(dir_fd_, "symlink.samedir", O_RDONLY));
313 EXPECT_OPEN_OK(openat(dir_fd_, "symlink.down", O_RDONLY));
314 EXPECT_OPEN_OK(openat(dir_fd_, "symlink.absolute_out", O_RDONLY));
315 EXPECT_OPEN_OK(openat(dir_fd_, "symlink.relative_in", O_RDONLY));
316 EXPECT_OPEN_OK(openat(dir_fd_, "symlink.relative_out", O_RDONLY));
317 EXPECT_OPEN_OK(openat(sub_fd_, "symlink.absolute_in", O_RDONLY));
318 EXPECT_OPEN_OK(openat(sub_fd_, "symlink.up", O_RDONLY));
319
320 // Now make both DFDs into Capsicum capabilities.
321 cap_rights_t r_rl;
322 cap_rights_init(&r_rl, CAP_READ, CAP_LOOKUP, CAP_FCHDIR);
323 EXPECT_OK(cap_rights_limit(dir_fd_, &r_rl));
324 EXPECT_OK(cap_rights_limit(sub_fd_, &r_rl));
325 CheckPolicing(0);
326 // Use of AT_FDCWD is independent of use of a capability.
327 // Can open paths starting with "/" against a capability dfd, because the dfd is ignored.
328 }
329
FORK_TEST_F(OpenatTest,InCapabilityMode)330 FORK_TEST_F(OpenatTest, InCapabilityMode) {
331 EXPECT_OK(cap_enter()); // Enter capability mode
332 CheckPolicing(0);
333
334 // Use of AT_FDCWD is banned in capability mode.
335 EXPECT_CAPMODE(openat(AT_FDCWD, "topfile", O_RDONLY));
336 EXPECT_CAPMODE(openat(AT_FDCWD, "subdir/bottomfile", O_RDONLY));
337 EXPECT_CAPMODE(openat(AT_FDCWD, "/etc/passwd", O_RDONLY));
338
339 // Can't open paths starting with "/" in capability mode.
340 EXPECT_OPENAT_FAIL_TRAVERSAL(dir_fd_, "/etc/passwd", O_RDONLY);
341 EXPECT_OPENAT_FAIL_TRAVERSAL(sub_fd_, "/etc/passwd", O_RDONLY);
342 }
343
344 #if !defined(O_RESOLVE_BENEATH) && defined(O_BENEATH)
345 #define O_RESOLVE_BENEATH O_BENEATH
346 #endif
347
348 #ifdef O_RESOLVE_BENEATH
TEST_F(OpenatTest,WithFlag)349 TEST_F(OpenatTest, WithFlag) {
350 CheckPolicing(O_RESOLVE_BENEATH);
351
352 // Check with AT_FDCWD.
353 EXPECT_OPEN_OK(openat(AT_FDCWD, "topfile", O_RDONLY|O_RESOLVE_BENEATH));
354 EXPECT_OPEN_OK(openat(AT_FDCWD, "subdir/bottomfile", O_RDONLY|O_RESOLVE_BENEATH));
355
356 // Can't open paths starting with "/" with O_RESOLVE_BENEATH specified.
357 EXPECT_OPENAT_FAIL_TRAVERSAL(AT_FDCWD, "/etc/passwd", O_RDONLY|O_RESOLVE_BENEATH);
358 EXPECT_OPENAT_FAIL_TRAVERSAL(dir_fd_, "/etc/passwd", O_RDONLY|O_RESOLVE_BENEATH);
359 EXPECT_OPENAT_FAIL_TRAVERSAL(sub_fd_, "/etc/passwd", O_RDONLY|O_RESOLVE_BENEATH);
360 }
361
FORK_TEST_F(OpenatTest,WithFlagInCapabilityMode)362 FORK_TEST_F(OpenatTest, WithFlagInCapabilityMode) {
363 EXPECT_OK(cap_enter()); // Enter capability mode
364 CheckPolicing(O_RESOLVE_BENEATH);
365 }
366 #endif
367