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