[PATCH v2 2/4] selftests/landlock: Selftests for file truncation support
Günther Noack
gnoack3000 at gmail.com
Tue Jul 12 21:14:03 UTC 2022
These tests exercise the following truncation operations:
* truncate() and trunate64() (truncate by path)
* ftruncate() and ftruncate64() (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:
* The truncate right is required to use ftruncate,
even when the thread already has the right to write to the file.
* 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.
Signed-off-by: Günther Noack <gnoack3000 at gmail.com>
Link: https://lore.kernel.org/all/20220707200612.132705-3-gnoack3000@gmail.com/
---
tools/testing/selftests/landlock/fs_test.c | 238 +++++++++++++++++++++
1 file changed, 238 insertions(+)
diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index cb77eaa01c91..1e5660118bce 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -3023,6 +3023,244 @@ TEST_F_FORK(layout1, proc_pipe)
ASSERT_EQ(0, close(pipe_fds[1]));
}
+TEST_F_FORK(layout1, truncate)
+{
+ const char *file_rwt = file1_s1d1;
+ const char *file_rw = file2_s1d1;
+ const char *file_rt = file1_s1d2;
+ const char *file_t = file2_s1d2;
+ const char *file_none = file1_s1d3;
+ const char *dir_t = dir_s2d1;
+ const char *file_in_dir_t = file1_s2d1;
+ 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,
+ },
+ {},
+ };
+ const __u64 handled = LANDLOCK_ACCESS_FS_READ_FILE |
+ LANDLOCK_ACCESS_FS_WRITE_FILE |
+ LANDLOCK_ACCESS_FS_TRUNCATE;
+ const int ruleset_fd = create_ruleset(_metadata, handled, rules);
+ struct stat statbuf;
+ int reg_fd;
+
+ ASSERT_LE(0, ruleset_fd);
+ enforce_ruleset(_metadata, ruleset_fd);
+ ASSERT_EQ(0, close(ruleset_fd));
+
+ /* Checks read, write and truncate rights: truncate and ftruncate work. */
+ reg_fd = open(file_rwt, O_WRONLY | O_CLOEXEC);
+ ASSERT_LE(0, reg_fd);
+ EXPECT_EQ(0, ftruncate(reg_fd, 10));
+ EXPECT_EQ(0, ftruncate64(reg_fd, 20));
+ ASSERT_EQ(0, close(reg_fd));
+
+ EXPECT_EQ(0, truncate(file_rwt, 10));
+ EXPECT_EQ(0, truncate64(file_rwt, 20));
+
+ reg_fd = open(file_rwt, O_WRONLY | O_TRUNC | O_CLOEXEC);
+ ASSERT_LE(0, reg_fd);
+ ASSERT_EQ(0, close(reg_fd));
+
+ reg_fd = open(file_rwt, O_RDONLY | O_TRUNC | O_CLOEXEC);
+ ASSERT_LE(0, reg_fd);
+ ASSERT_EQ(0, close(reg_fd));
+
+ /* Checks read and write rights: no truncate variant works. */
+ reg_fd = open(file_rw, O_WRONLY | O_CLOEXEC);
+ ASSERT_LE(0, reg_fd);
+ EXPECT_EQ(-1, ftruncate(reg_fd, 10));
+ EXPECT_EQ(EACCES, errno);
+ EXPECT_EQ(-1, ftruncate64(reg_fd, 20));
+ EXPECT_EQ(EACCES, errno);
+ ASSERT_EQ(0, close(reg_fd));
+
+ EXPECT_EQ(-1, truncate(file_rw, 10));
+ EXPECT_EQ(EACCES, errno);
+ EXPECT_EQ(-1, truncate64(file_rw, 20));
+ EXPECT_EQ(EACCES, errno);
+
+ EXPECT_EQ(-1, open(file_rw, O_WRONLY | O_TRUNC | O_CLOEXEC));
+ EXPECT_EQ(EACCES, errno);
+
+ EXPECT_EQ(-1, open(file_rw, O_RDONLY | O_TRUNC | O_CLOEXEC));
+ EXPECT_EQ(EACCES, errno);
+
+ /* Checks read and truncate right: truncate works, also with open(2). */
+ EXPECT_EQ(-1, open(file_rt, O_WRONLY | O_CLOEXEC));
+ EXPECT_EQ(EACCES, errno);
+
+ EXPECT_EQ(0, truncate(file_rt, 10));
+ EXPECT_EQ(0, truncate64(file_rt, 20));
+
+ reg_fd = open(file_rt, O_RDONLY | O_TRUNC | O_CLOEXEC);
+ ASSERT_LE(0, reg_fd);
+ ASSERT_EQ(0, fstat(reg_fd, &statbuf));
+ EXPECT_EQ(0, statbuf.st_size);
+ ASSERT_EQ(0, close(reg_fd));
+
+ /* Checks truncate right: truncate works, but can't open file. */
+ EXPECT_EQ(-1, open(file_t, O_WRONLY | O_CLOEXEC));
+ EXPECT_EQ(EACCES, errno);
+
+ EXPECT_EQ(0, truncate(file_t, 10));
+ EXPECT_EQ(0, truncate64(file_t, 20));
+
+ EXPECT_EQ(-1, open(file_t, O_RDONLY | O_TRUNC | O_CLOEXEC));
+ EXPECT_EQ(EACCES, errno);
+
+ /* Checks "no rights" case: No form of truncation works. */
+ EXPECT_EQ(-1, open(file_none, O_WRONLY | O_CLOEXEC));
+ EXPECT_EQ(EACCES, errno);
+
+ EXPECT_EQ(-1, truncate(file_none, 10));
+ EXPECT_EQ(EACCES, errno);
+ EXPECT_EQ(-1, truncate64(file_none, 20));
+ EXPECT_EQ(EACCES, errno);
+
+ EXPECT_EQ(-1, open(file_none, O_RDONLY | O_TRUNC | O_CLOEXEC));
+ EXPECT_EQ(EACCES, errno);
+
+ /* Checks truncate right on directory: */
+ EXPECT_EQ(-1, open(file_in_dir_t, O_WRONLY | O_CLOEXEC));
+ EXPECT_EQ(EACCES, errno);
+
+ EXPECT_EQ(0, truncate(file_in_dir_t, 10));
+ EXPECT_EQ(0, truncate64(file_in_dir_t, 20));
+
+ EXPECT_EQ(-1, open(file_in_dir_t, O_RDONLY | O_TRUNC | O_CLOEXEC));
+ EXPECT_EQ(EACCES, errno);
+}
+
+/*
+ * 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 *file_r = file1_s1d1;
+ const char *file_w = file2_s1d1;
+ const char *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;
+ const int ruleset_fd = create_ruleset(_metadata, handled, rules);
+ int reg_fd;
+
+ ASSERT_LE(0, ruleset_fd);
+ enforce_ruleset(_metadata, ruleset_fd);
+ ASSERT_EQ(0, close(ruleset_fd));
+
+ /* Checks read right: truncation should work through truncate and open. */
+ EXPECT_EQ(0, truncate(file_r, 10));
+ EXPECT_EQ(0, truncate64(file_r, 20));
+
+ reg_fd = open(file_r, O_RDONLY | O_TRUNC | O_CLOEXEC);
+ ASSERT_LE(0, reg_fd);
+ ASSERT_EQ(0, close(reg_fd));
+
+ EXPECT_EQ(-1, open(file_r, O_WRONLY | O_TRUNC | O_CLOEXEC));
+ EXPECT_EQ(EACCES, errno);
+
+ /* Checks write right: truncation should work through truncate, ftruncate and open. */
+ EXPECT_EQ(0, truncate(file_w, 10));
+ EXPECT_EQ(0, truncate64(file_w, 20));
+
+ EXPECT_EQ(-1, open(file_w, O_RDONLY | O_TRUNC | O_CLOEXEC));
+ EXPECT_EQ(EACCES, errno);
+
+ reg_fd = open(file_w, O_WRONLY | O_TRUNC | O_CLOEXEC);
+ ASSERT_LE(0, reg_fd);
+ ASSERT_EQ(0, close(reg_fd));
+
+ reg_fd = open(file_w, O_WRONLY);
+ ASSERT_LE(0, reg_fd);
+ EXPECT_EQ(0, ftruncate(reg_fd, 10));
+ EXPECT_EQ(0, ftruncate64(reg_fd, 20));
+ ASSERT_EQ(0, close(reg_fd));
+
+ /* Checks "no rights" case: truncate works but all open attempts fail. */
+ EXPECT_EQ(0, truncate(file_none, 10));
+ EXPECT_EQ(0, truncate64(file_none, 20));
+
+ EXPECT_EQ(-1, open(file_none, O_RDONLY | O_TRUNC | O_CLOEXEC));
+ EXPECT_EQ(EACCES, errno);
+
+ EXPECT_EQ(-1, open(file_none, O_WRONLY | O_TRUNC | O_CLOEXEC));
+ EXPECT_EQ(EACCES, errno);
+
+ EXPECT_EQ(-1, open(file_none, O_WRONLY | O_CLOEXEC));
+ EXPECT_EQ(EACCES, errno);
+}
+
+/* Exercises creat(), which is equivalent to an open with O_CREAT|O_WRONLY|O_TRUNC. */
+TEST_F_FORK(layout1, truncate_creat)
+{
+ const struct rule rules[] = {
+ {
+ .path = dir_s1d1,
+ .access = LANDLOCK_ACCESS_FS_WRITE_FILE,
+ },
+ {}
+ };
+ const __u64 handled = LANDLOCK_ACCESS_FS_WRITE_FILE |
+ LANDLOCK_ACCESS_FS_TRUNCATE;
+ const int ruleset_fd = create_ruleset(_metadata, handled, rules);
+ int reg_fd;
+
+ ASSERT_LE(0, ruleset_fd);
+ enforce_ruleset(_metadata, ruleset_fd);
+ ASSERT_EQ(0, close(ruleset_fd));
+
+ /* Checks creating a new file: This should work even without the truncate right. */
+ ASSERT_EQ(0, unlink(file1_s1d1));
+
+ reg_fd = creat(file1_s1d1, 0600);
+ ASSERT_LE(0, reg_fd);
+ ASSERT_EQ(0, close(reg_fd));
+
+ /*
+ * Checks creating a file over an existing one:
+ * This should fail. It would truncate the file, and we don't have that right.
+ */
+ EXPECT_EQ(-1, creat(file2_s1d1, 0600));
+ EXPECT_EQ(EACCES, errno);
+}
+
/* clang-format off */
FIXTURE(layout1_bind) {};
/* clang-format on */
--
2.37.0
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