[PATCH -next v2 3/6] landlock: add chmod and chown support
From: Xiu Jianfeng
Date: Sat Aug 27 2022 - 07:16:15 EST
Add two flags LANDLOCK_ACCESS_FS_CHMOD and LANDLOCK_ACCESS_FS_CHGRP to
support restriction to chmod(2) and chown(2) with landlock.
If these two access rights are set on a directory, they only take effect
for its context, not the directory itself.
This patch also change the landlock ABI version from 3 to 4.
Signed-off-by: Xiu Jianfeng <xiujianfeng@xxxxxxxxxx>
---
include/uapi/linux/landlock.h | 10 +++--
security/landlock/fs.c | 43 +++++++++++++++++++-
security/landlock/limits.h | 2 +-
security/landlock/syscalls.c | 2 +-
tools/testing/selftests/landlock/base_test.c | 2 +-
tools/testing/selftests/landlock/fs_test.c | 6 ++-
6 files changed, 56 insertions(+), 9 deletions(-)
diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
index 735b1fe8326e..07b73626ff20 100644
--- a/include/uapi/linux/landlock.h
+++ b/include/uapi/linux/landlock.h
@@ -141,14 +141,16 @@ struct landlock_path_beneath_attr {
* directory) parent. Otherwise, such actions are denied with errno set to
* EACCES. The EACCES errno prevails over EXDEV to let user space
* efficiently deal with an unrecoverable error.
+ * - %LANDLOCK_ACCESS_FS_CHMOD: Change the file mode bits of a file.
+ * - %LANDLOCK_ACCESS_FS_CHGRP: Change the owner and/or group of a file.
*
* .. warning::
*
* It is currently not possible to restrict some file-related actions
* 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:`stat(2)`, :manpage:`flock(2)`, :manpage:`setxattr(2)`,
+ * :manpage:`utime(2)`,:manpage:`ioctl(2)`, :manpage:`fcntl(2)`,
+ * :manpage:`access(2)`.
* Future Landlock evolutions will enable to restrict them.
*/
/* clang-format off */
@@ -167,6 +169,8 @@ 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_CHMOD (1ULL << 15)
+#define LANDLOCK_ACCESS_FS_CHGRP (1ULL << 16)
/* clang-format on */
#endif /* _UAPI_LINUX_LANDLOCK_H */
diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 4ef614a4ea22..6ac83d96ada7 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -185,7 +185,9 @@ 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_CHMOD | \
+ LANDLOCK_ACCESS_FS_CHGRP)
/* clang-format on */
/*
@@ -690,6 +692,31 @@ static inline int current_check_access_path(const struct path *const path,
return check_access_path(dom, path, access_request);
}
+static inline int
+current_check_access_path_context_only(const struct path *const path,
+ const access_mask_t access_request)
+{
+ const struct landlock_ruleset *const dom =
+ landlock_get_current_domain();
+ struct path eff_path;
+ int ret;
+
+ if (!dom)
+ return 0;
+ eff_path = *path;
+ /* if it's dir, check its visible parent. */
+ if (d_is_dir(eff_path.dentry)) {
+ path_get(&eff_path);
+ /* dont care if reaches the root or not. */
+ walk_to_visible_parent(&eff_path);
+ ret = current_check_access_path(&eff_path, access_request);
+ path_put(&eff_path);
+ } else {
+ ret = current_check_access_path(&eff_path, access_request);
+ }
+ return ret;
+}
+
static inline access_mask_t get_mode_access(const umode_t mode)
{
switch (mode & S_IFMT) {
@@ -1177,6 +1204,18 @@ static int hook_path_truncate(const struct path *const path)
return current_check_access_path(path, LANDLOCK_ACCESS_FS_TRUNCATE);
}
+static int hook_path_chmod(const struct path *const path, umode_t mode)
+{
+ return current_check_access_path_context_only(path,
+ LANDLOCK_ACCESS_FS_CHMOD);
+}
+
+static int hook_path_chown(const struct path *const path, kuid_t uid, kgid_t gid)
+{
+ return current_check_access_path_context_only(path,
+ LANDLOCK_ACCESS_FS_CHGRP);
+}
+
/* File hooks */
static inline access_mask_t get_file_access(const struct file *const file)
@@ -1230,6 +1269,8 @@ static struct security_hook_list landlock_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(path_unlink, hook_path_unlink),
LSM_HOOK_INIT(path_rmdir, hook_path_rmdir),
LSM_HOOK_INIT(path_truncate, hook_path_truncate),
+ LSM_HOOK_INIT(path_chmod, hook_path_chmod),
+ LSM_HOOK_INIT(path_chown, hook_path_chown),
LSM_HOOK_INIT(file_open, hook_file_open),
};
diff --git a/security/landlock/limits.h b/security/landlock/limits.h
index 82288f0e9e5e..7cdd7d467d12 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_CHGRP
#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/security/landlock/syscalls.c b/security/landlock/syscalls.c
index f4d6fc7ed17f..469e0e11735c 100644
--- a/security/landlock/syscalls.c
+++ b/security/landlock/syscalls.c
@@ -129,7 +129,7 @@ static const struct file_operations ruleset_fops = {
.write = fop_dummy_write,
};
-#define LANDLOCK_ABI_VERSION 3
+#define LANDLOCK_ABI_VERSION 4
/**
* sys_landlock_create_ruleset - Create a new ruleset
diff --git a/tools/testing/selftests/landlock/base_test.c b/tools/testing/selftests/landlock/base_test.c
index 72cdae277b02..9f00582f639c 100644
--- a/tools/testing/selftests/landlock/base_test.c
+++ b/tools/testing/selftests/landlock/base_test.c
@@ -75,7 +75,7 @@ TEST(abi_version)
const struct landlock_ruleset_attr ruleset_attr = {
.handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE,
};
- ASSERT_EQ(3, landlock_create_ruleset(NULL, 0,
+ ASSERT_EQ(4, landlock_create_ruleset(NULL, 0,
LANDLOCK_CREATE_RULESET_VERSION));
ASSERT_EQ(-1, landlock_create_ruleset(&ruleset_attr, 0,
diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index debe2d9ea6cf..f513cd8d9d51 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -404,9 +404,11 @@ 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_CHMOD | \
+ LANDLOCK_ACCESS_FS_CHGRP)
-#define ACCESS_LAST LANDLOCK_ACCESS_FS_TRUNCATE
+#define ACCESS_LAST LANDLOCK_ACCESS_FS_CHGRP
#define ACCESS_ALL ( \
ACCESS_FILE | \
--
2.17.1