[PATCH v7 3/7] selftests/landlock: Selftests for file truncation support
Günther Noack
gnoack3000 at gmail.com
Fri Sep 30 16:01:40 UTC 2022
These tests exercise the following truncation operations:
* truncate() (truncate by path)
* ftruncate() (truncate by file descriptor)
* open with the O_TRUNC flag
* special case: creat(), which is open with O_CREAT|O_WRONLY|O_TRUNC.
in the following scenarios:
* Files with read, write and truncate rights.
* Files with read and truncate rights.
* Files with the truncate right.
* Files without the truncate right.
In particular, the following scenarios are enforced with the test:
* open() with O_TRUNC requires the truncate right, if it truncates a file.
open() already checks security_path_truncate() in this case,
and it required no additional check in the Landlock LSM's file_open hook.
* creat() requires the truncate right
when called with an existing filename.
* creat() does *not* require the truncate right
when it's creating a new file.
* ftruncate() requires that the file was opened by a thread that had
the truncate right for the file at the time of open(). (The rights
are carried along with the opened file.)
Signed-off-by: Günther Noack <gnoack3000 at gmail.com>
---
tools/testing/selftests/landlock/fs_test.c | 287 +++++++++++++++++++++
1 file changed, 287 insertions(+)
diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 87b28d14a1aa..718543fd3dfc 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -58,6 +58,7 @@ static const char file1_s2d3[] = TMP_DIR "/s2d1/s2d2/s2d3/f1";
static const char file2_s2d3[] = TMP_DIR "/s2d1/s2d2/s2d3/f2";
static const char dir_s3d1[] = TMP_DIR "/s3d1";
+static const char file1_s3d1[] = TMP_DIR "/s3d1/f1";
/* dir_s3d2 is a mount point. */
static const char dir_s3d2[] = TMP_DIR "/s3d1/s3d2";
static const char dir_s3d3[] = TMP_DIR "/s3d1/s3d2/s3d3";
@@ -83,6 +84,7 @@ static const char dir_s3d3[] = TMP_DIR "/s3d1/s3d2/s3d3";
* │ ├── f1
* │ └── f2
* └── s3d1
+ * ├── f1
* └── s3d2
* └── s3d3
*/
@@ -208,6 +210,7 @@ static void create_layout1(struct __test_metadata *const _metadata)
create_file(_metadata, file1_s2d3);
create_file(_metadata, file2_s2d3);
+ create_file(_metadata, file1_s3d1);
create_directory(_metadata, dir_s3d2);
set_cap(_metadata, CAP_SYS_ADMIN);
ASSERT_EQ(0, mount("tmp", dir_s3d2, "tmpfs", 0, "size=4m,mode=700"));
@@ -230,6 +233,7 @@ static void remove_layout1(struct __test_metadata *const _metadata)
EXPECT_EQ(0, remove_path(file1_s2d2));
EXPECT_EQ(0, remove_path(file1_s2d1));
+ EXPECT_EQ(0, remove_path(file1_s3d1));
EXPECT_EQ(0, remove_path(dir_s3d3));
set_cap(_metadata, CAP_SYS_ADMIN);
umount(dir_s3d2);
@@ -3158,6 +3162,289 @@ TEST_F_FORK(layout1, proc_pipe)
ASSERT_EQ(0, close(pipe_fds[1]));
}
+/* Invokes truncate(2) and returns its errno or 0. */
+static int test_truncate(const char *const path)
+{
+ if (truncate(path, 10) < 0)
+ return errno;
+ return 0;
+}
+
+/*
+ * Invokes creat(2) and returns its errno or 0.
+ * Closes the opened file descriptor on success.
+ */
+static int test_creat(const char *const path)
+{
+ int fd = creat(path, 0600);
+
+ if (fd < 0)
+ return errno;
+
+ /*
+ * Mixing error codes from close(2) and creat(2) should not lead to any
+ * (access type) confusion for this test.
+ */
+ if (close(fd) < 0)
+ return errno;
+ return 0;
+}
+
+/*
+ * Exercises file truncation when it's not restricted,
+ * as it was the case before LANDLOCK_ACCESS_FS_TRUNCATE existed.
+ */
+TEST_F_FORK(layout1, truncate_unhandled)
+{
+ const char *const file_r = file1_s1d1;
+ const char *const file_w = file2_s1d1;
+ const char *const file_none = file1_s1d2;
+ const struct rule rules[] = {
+ {
+ .path = file_r,
+ .access = LANDLOCK_ACCESS_FS_READ_FILE,
+ },
+ {
+ .path = file_w,
+ .access = LANDLOCK_ACCESS_FS_WRITE_FILE,
+ },
+ /* Implicitly: No rights for file_none. */
+ {},
+ };
+
+ const __u64 handled = LANDLOCK_ACCESS_FS_READ_FILE |
+ LANDLOCK_ACCESS_FS_WRITE_FILE;
+ int ruleset_fd;
+
+ /* Enable Landlock. */
+ ruleset_fd = create_ruleset(_metadata, handled, rules);
+
+ ASSERT_LE(0, ruleset_fd);
+ enforce_ruleset(_metadata, ruleset_fd);
+ ASSERT_EQ(0, close(ruleset_fd));
+
+ /*
+ * Checks read right: truncate and open with O_TRUNC work, unless the
+ * file is attempted to be opened for writing.
+ */
+ EXPECT_EQ(0, test_truncate(file_r));
+ EXPECT_EQ(0, test_open(file_r, O_RDONLY | O_TRUNC));
+ EXPECT_EQ(EACCES, test_open(file_r, O_WRONLY | O_TRUNC));
+ EXPECT_EQ(EACCES, test_creat(file_r));
+
+ /*
+ * Checks write right: truncate and open with O_TRUNC work, unless the
+ * file is attempted to be opened for reading.
+ */
+ EXPECT_EQ(0, test_truncate(file_w));
+ EXPECT_EQ(EACCES, test_open(file_w, O_RDONLY | O_TRUNC));
+ EXPECT_EQ(0, test_open(file_w, O_WRONLY | O_TRUNC));
+ EXPECT_EQ(0, test_creat(file_w));
+
+ /*
+ * Checks "no rights" case: truncate works but all open attempts fail,
+ * including creat.
+ */
+ EXPECT_EQ(0, test_truncate(file_none));
+ EXPECT_EQ(EACCES, test_open(file_none, O_RDONLY | O_TRUNC));
+ EXPECT_EQ(EACCES, test_open(file_none, O_WRONLY | O_TRUNC));
+ EXPECT_EQ(EACCES, test_creat(file_none));
+}
+
+TEST_F_FORK(layout1, truncate)
+{
+ const char *const file_rwt = file1_s1d1;
+ const char *const file_rw = file2_s1d1;
+ const char *const file_rt = file1_s1d2;
+ const char *const file_t = file2_s1d2;
+ const char *const file_none = file1_s1d3;
+ const char *const dir_t = dir_s2d1;
+ const char *const file_in_dir_t = file1_s2d1;
+ const char *const dir_w = dir_s3d1;
+ const char *const file_in_dir_w = file1_s3d1;
+ const struct rule rules[] = {
+ {
+ .path = file_rwt,
+ .access = LANDLOCK_ACCESS_FS_READ_FILE |
+ LANDLOCK_ACCESS_FS_WRITE_FILE |
+ LANDLOCK_ACCESS_FS_TRUNCATE,
+ },
+ {
+ .path = file_rw,
+ .access = LANDLOCK_ACCESS_FS_READ_FILE |
+ LANDLOCK_ACCESS_FS_WRITE_FILE,
+ },
+ {
+ .path = file_rt,
+ .access = LANDLOCK_ACCESS_FS_READ_FILE |
+ LANDLOCK_ACCESS_FS_TRUNCATE,
+ },
+ {
+ .path = file_t,
+ .access = LANDLOCK_ACCESS_FS_TRUNCATE,
+ },
+ /* Implicitly: No access rights for file_none. */
+ {
+ .path = dir_t,
+ .access = LANDLOCK_ACCESS_FS_TRUNCATE,
+ },
+ {
+ .path = dir_w,
+ .access = LANDLOCK_ACCESS_FS_WRITE_FILE,
+ },
+ {},
+ };
+ const __u64 handled = LANDLOCK_ACCESS_FS_READ_FILE |
+ LANDLOCK_ACCESS_FS_WRITE_FILE |
+ LANDLOCK_ACCESS_FS_TRUNCATE;
+ int ruleset_fd;
+
+ /* Enable Landlock. */
+ ruleset_fd = create_ruleset(_metadata, handled, rules);
+
+ ASSERT_LE(0, ruleset_fd);
+ enforce_ruleset(_metadata, ruleset_fd);
+ ASSERT_EQ(0, close(ruleset_fd));
+
+ /* Checks read, write and truncate rights: truncation works. */
+ EXPECT_EQ(0, test_truncate(file_rwt));
+ EXPECT_EQ(0, test_open(file_rwt, O_RDONLY | O_TRUNC));
+ EXPECT_EQ(0, test_open(file_rwt, O_WRONLY | O_TRUNC));
+
+ /* Checks read and write rights: no truncate variant works. */
+ EXPECT_EQ(EACCES, test_truncate(file_rw));
+ EXPECT_EQ(EACCES, test_open(file_rw, O_RDONLY | O_TRUNC));
+ EXPECT_EQ(EACCES, test_open(file_rw, O_WRONLY | O_TRUNC));
+
+ /*
+ * Checks read and truncate rights: truncation works.
+ *
+ * Note: Files can get truncated using open() even with O_RDONLY.
+ */
+ EXPECT_EQ(0, test_truncate(file_rt));
+ EXPECT_EQ(0, test_open(file_rt, O_RDONLY | O_TRUNC));
+ EXPECT_EQ(EACCES, test_open(file_rt, O_WRONLY | O_TRUNC));
+
+ /* Checks truncate right: truncate works, but can't open file. */
+ EXPECT_EQ(0, test_truncate(file_t));
+ EXPECT_EQ(EACCES, test_open(file_t, O_RDONLY | O_TRUNC));
+ EXPECT_EQ(EACCES, test_open(file_t, O_WRONLY | O_TRUNC));
+
+ /* Checks "no rights" case: No form of truncation works. */
+ EXPECT_EQ(EACCES, test_truncate(file_none));
+ EXPECT_EQ(EACCES, test_open(file_none, O_RDONLY | O_TRUNC));
+ EXPECT_EQ(EACCES, test_open(file_none, O_WRONLY | O_TRUNC));
+
+ /*
+ * Checks truncate right on directory: truncate works on contained
+ * files.
+ */
+ EXPECT_EQ(0, test_truncate(file_in_dir_t));
+ EXPECT_EQ(EACCES, test_open(file_in_dir_t, O_RDONLY | O_TRUNC));
+ EXPECT_EQ(EACCES, test_open(file_in_dir_t, O_WRONLY | O_TRUNC));
+
+ /*
+ * Checks creat in dir_w: This requires the truncate right when
+ * overwriting an existing file, but does not require it when the file
+ * is new.
+ */
+ EXPECT_EQ(EACCES, test_creat(file_in_dir_w));
+
+ ASSERT_EQ(0, unlink(file_in_dir_w));
+ EXPECT_EQ(0, test_creat(file_in_dir_w));
+}
+
+/* Invokes ftruncate(2) and returns its errno or 0. */
+static int test_ftruncate(int fd)
+{
+ if (ftruncate(fd, 10) < 0)
+ return errno;
+ return 0;
+}
+
+TEST_F_FORK(layout1, ftruncate)
+{
+ /*
+ * This test opens a new file descriptor at different stages of
+ * Landlock restriction:
+ *
+ * without restriction: ftruncate works
+ * something else but truncate restricted: ftruncate works
+ * truncate restricted and permitted: ftruncate works
+ * truncate restricted and not permitted: ftruncate fails
+ *
+ * Whether this works or not is expected to depend on the time when the
+ * FD was opened, not to depend on the time when ftruncate() was
+ * called.
+ */
+ const char *const path = file1_s1d1;
+ const __u64 handled1 = LANDLOCK_ACCESS_FS_READ_FILE |
+ LANDLOCK_ACCESS_FS_WRITE_FILE;
+ const struct rule layer1[] = {
+ {
+ .path = path,
+ .access = LANDLOCK_ACCESS_FS_WRITE_FILE,
+ },
+ {},
+ };
+ const __u64 handled2 = LANDLOCK_ACCESS_FS_TRUNCATE;
+ const struct rule layer2[] = {
+ {
+ .path = path,
+ .access = LANDLOCK_ACCESS_FS_TRUNCATE,
+ },
+ {},
+ };
+ const __u64 handled3 = LANDLOCK_ACCESS_FS_TRUNCATE |
+ LANDLOCK_ACCESS_FS_WRITE_FILE;
+ const struct rule layer3[] = {
+ {
+ .path = path,
+ .access = LANDLOCK_ACCESS_FS_WRITE_FILE,
+ },
+ {},
+ };
+ int fd_layer0, fd_layer1, fd_layer2, fd_layer3, ruleset_fd;
+
+ fd_layer0 = open(path, O_WRONLY);
+ EXPECT_EQ(0, test_ftruncate(fd_layer0));
+
+ ruleset_fd = create_ruleset(_metadata, handled1, layer1);
+ ASSERT_LE(0, ruleset_fd);
+ enforce_ruleset(_metadata, ruleset_fd);
+ ASSERT_EQ(0, close(ruleset_fd));
+
+ fd_layer1 = open(path, O_WRONLY);
+ EXPECT_EQ(0, test_ftruncate(fd_layer0));
+ EXPECT_EQ(0, test_ftruncate(fd_layer1));
+
+ ruleset_fd = create_ruleset(_metadata, handled2, layer2);
+ ASSERT_LE(0, ruleset_fd);
+ enforce_ruleset(_metadata, ruleset_fd);
+ ASSERT_EQ(0, close(ruleset_fd));
+
+ fd_layer2 = open(path, O_WRONLY);
+ EXPECT_EQ(0, test_ftruncate(fd_layer0));
+ EXPECT_EQ(0, test_ftruncate(fd_layer1));
+ EXPECT_EQ(0, test_ftruncate(fd_layer2));
+
+ ruleset_fd = create_ruleset(_metadata, handled3, layer3);
+ ASSERT_LE(0, ruleset_fd);
+ enforce_ruleset(_metadata, ruleset_fd);
+ ASSERT_EQ(0, close(ruleset_fd));
+
+ fd_layer3 = open(path, O_WRONLY);
+ EXPECT_EQ(0, test_ftruncate(fd_layer0));
+ EXPECT_EQ(0, test_ftruncate(fd_layer1));
+ EXPECT_EQ(0, test_ftruncate(fd_layer2));
+ EXPECT_EQ(EACCES, test_ftruncate(fd_layer3));
+
+ ASSERT_EQ(0, close(fd_layer0));
+ ASSERT_EQ(0, close(fd_layer1));
+ ASSERT_EQ(0, close(fd_layer2));
+ ASSERT_EQ(0, close(fd_layer3));
+}
+
/* clang-format off */
FIXTURE(layout1_bind) {};
/* clang-format on */
--
2.37.3
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