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