[PATCH v2 2/6] landlock: Add LANDLOCK_ACCESS_FS_IOCTL access right
Günther Noack
gnoack at google.com
Fri Jun 23 14:43:25 UTC 2023
Like the truncate right, this right is associated with a file
descriptor at the time of open(2), and gets respected even when the
file descriptor is used outside of the thread which it was originally
created in.
In particular, this happens for the commonly inherited file
descriptors stdin, stdout and stderr, if these are bound to a tty.
This means that programs using tty ioctls can drop the ioctl access
right, but continue using these ioctls on the already opened input and
output file descriptors.
Signed-off-by: Günther Noack <gnoack at google.com>
---
include/uapi/linux/landlock.h | 19 ++++++++++++-------
security/landlock/fs.c | 21 +++++++++++++++++++--
security/landlock/limits.h | 2 +-
tools/testing/selftests/landlock/fs_test.c | 5 +++--
4 files changed, 35 insertions(+), 12 deletions(-)
diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
index 81d09ef9aa50..57de1dc5869e 100644
--- a/include/uapi/linux/landlock.h
+++ b/include/uapi/linux/landlock.h
@@ -102,12 +102,16 @@ struct landlock_path_beneath_attr {
* - %LANDLOCK_ACCESS_FS_READ_FILE: Open a file with read access.
* - %LANDLOCK_ACCESS_FS_TRUNCATE: Truncate a file with :manpage:`truncate(2)`,
* :manpage:`ftruncate(2)`, :manpage:`creat(2)`, or :manpage:`open(2)` with
- * ``O_TRUNC``. Whether an opened file can be truncated with
- * :manpage:`ftruncate(2)` is determined during :manpage:`open(2)`, in the
- * same way as read and write permissions are checked during
- * :manpage:`open(2)` using %LANDLOCK_ACCESS_FS_READ_FILE and
- * %LANDLOCK_ACCESS_FS_WRITE_FILE. This access right is available since the
- * third version of the Landlock ABI.
+ * ``O_TRUNC``. This access right is available since the third version of the
+ * Landlock ABI.
+ * - %LANDLOCK_ACCESS_FS_IOCTL: Invoke :manpage:`ioctl(2)` on the opened file.
+ * This access right is available since the fourth version of the Landlock
+ * ABI.
+ *
+ * Whether an opened file can be truncated with :manpage:`ftruncate(2)` or used
+ * with `ioctl(2)` is determined during :manpage:`open(2)`, in the same way as
+ * read and write permissions are checked during :manpage:`open(2)` using
+ * %LANDLOCK_ACCESS_FS_READ_FILE and %LANDLOCK_ACCESS_FS_WRITE_FILE.
*
* A directory can receive access rights related to files or directories. The
* following access right is applied to the directory itself, and the
@@ -168,7 +172,7 @@ struct landlock_path_beneath_attr {
* accessible through these syscall families: :manpage:`chdir(2)`,
* :manpage:`stat(2)`, :manpage:`flock(2)`, :manpage:`chmod(2)`,
* :manpage:`chown(2)`, :manpage:`setxattr(2)`, :manpage:`utime(2)`,
- * :manpage:`ioctl(2)`, :manpage:`fcntl(2)`, :manpage:`access(2)`.
+ * :manpage:`fcntl(2)`, :manpage:`access(2)`.
* Future Landlock evolutions will enable to restrict them.
*/
/* clang-format off */
@@ -187,6 +191,7 @@ struct landlock_path_beneath_attr {
#define LANDLOCK_ACCESS_FS_MAKE_SYM (1ULL << 12)
#define LANDLOCK_ACCESS_FS_REFER (1ULL << 13)
#define LANDLOCK_ACCESS_FS_TRUNCATE (1ULL << 14)
+#define LANDLOCK_ACCESS_FS_IOCTL (1ULL << 15)
/* clang-format on */
#endif /* _UAPI_LINUX_LANDLOCK_H */
diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 1c0c198f6fdb..017863696610 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -147,7 +147,8 @@ static struct landlock_object *get_inode_object(struct inode *const inode)
LANDLOCK_ACCESS_FS_EXECUTE | \
LANDLOCK_ACCESS_FS_WRITE_FILE | \
LANDLOCK_ACCESS_FS_READ_FILE | \
- LANDLOCK_ACCESS_FS_TRUNCATE)
+ LANDLOCK_ACCESS_FS_TRUNCATE | \
+ LANDLOCK_ACCESS_FS_IOCTL)
/* clang-format on */
/*
@@ -1207,7 +1208,8 @@ static int hook_file_open(struct file *const file)
{
layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS] = {};
access_mask_t open_access_request, full_access_request, allowed_access;
- const access_mask_t optional_access = LANDLOCK_ACCESS_FS_TRUNCATE;
+ const access_mask_t optional_access = LANDLOCK_ACCESS_FS_TRUNCATE |
+ LANDLOCK_ACCESS_FS_IOCTL;
const struct landlock_ruleset *const dom =
landlock_get_current_domain();
@@ -1280,6 +1282,20 @@ static int hook_file_truncate(struct file *const file)
return -EACCES;
}
+static int hook_file_ioctl(struct file *file, unsigned int cmd,
+ unsigned long arg)
+{
+ /*
+ * It is the access rights at the time of opening the file which
+ * determine whether ioctl can be used on the opened file later.
+ *
+ * The access right is attached to the opened file in hook_file_open().
+ */
+ if (landlock_file(file)->allowed_access & LANDLOCK_ACCESS_FS_IOCTL)
+ return 0;
+ return -EACCES;
+}
+
static struct security_hook_list landlock_hooks[] __ro_after_init = {
LSM_HOOK_INIT(inode_free_security, hook_inode_free_security),
@@ -1302,6 +1318,7 @@ static struct security_hook_list landlock_hooks[] __ro_after_init = {
LSM_HOOK_INIT(file_alloc_security, hook_file_alloc_security),
LSM_HOOK_INIT(file_open, hook_file_open),
LSM_HOOK_INIT(file_truncate, hook_file_truncate),
+ LSM_HOOK_INIT(file_ioctl, hook_file_ioctl),
};
__init void landlock_add_fs_hooks(void)
diff --git a/security/landlock/limits.h b/security/landlock/limits.h
index 82288f0e9e5e..40d8f17698b6 100644
--- a/security/landlock/limits.h
+++ b/security/landlock/limits.h
@@ -18,7 +18,7 @@
#define LANDLOCK_MAX_NUM_LAYERS 16
#define LANDLOCK_MAX_NUM_RULES U32_MAX
-#define LANDLOCK_LAST_ACCESS_FS LANDLOCK_ACCESS_FS_TRUNCATE
+#define LANDLOCK_LAST_ACCESS_FS LANDLOCK_ACCESS_FS_IOCTL
#define LANDLOCK_MASK_ACCESS_FS ((LANDLOCK_LAST_ACCESS_FS << 1) - 1)
#define LANDLOCK_NUM_ACCESS_FS __const_hweight64(LANDLOCK_MASK_ACCESS_FS)
diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 83d565569512..09dd1eaac8a9 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -523,9 +523,10 @@ TEST_F_FORK(layout1, inval)
LANDLOCK_ACCESS_FS_EXECUTE | \
LANDLOCK_ACCESS_FS_WRITE_FILE | \
LANDLOCK_ACCESS_FS_READ_FILE | \
- LANDLOCK_ACCESS_FS_TRUNCATE)
+ LANDLOCK_ACCESS_FS_TRUNCATE | \
+ LANDLOCK_ACCESS_FS_IOCTL)
-#define ACCESS_LAST LANDLOCK_ACCESS_FS_TRUNCATE
+#define ACCESS_LAST LANDLOCK_ACCESS_FS_IOCTL
#define ACCESS_ALL ( \
ACCESS_FILE | \
--
2.41.0.162.gfafddb0af9-goog
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