[PATCH v3 1/6] Landlock: Add signal control

[Tahera Fahimi]

Currently, a sandbox process is not restricted to send a signal
(e.g. SIGKILL) to a process outside of the sandbox environment.
Ability to sending a signal for a sandboxed process should be
scoped the same way abstract unix sockets are scoped. Therefore,
we extend "scoped" field in a ruleset with
"LANDLOCK_SCOPED_SIGNAL" to specify that a ruleset will deny
sending any signal from within a sandbox process to its
parent(i.e. any parent sandbox or non-sandboxed procsses).

Signed-off-by: Tahera Fahimi <fahimitahera at gmail.com>
---
Changes in versions:
V3:
* Moving file_send_sigiotask to another patch.
* Minor code refactoring.
V2:
* Remove signal_is_scoped function
* Applying reviews of V1
V1:
* Introducing LANDLOCK_SCOPE_SIGNAL
* Adding two hooks, hook_task_kill and hook_file_send_sigiotask
  for signal scoping.
---
 include/uapi/linux/landlock.h |  3 +++
 security/landlock/limits.h    |  2 +-
 security/landlock/task.c      | 27 +++++++++++++++++++++++++++
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
index 057a4811ed06..46301b47f502 100644
--- a/include/uapi/linux/landlock.h
+++ b/include/uapi/linux/landlock.h
@@ -289,8 +289,11 @@ struct landlock_net_port_attr {
  *   from connecting to an abstract unix socket created by a process
  *   outside the related Landlock domain (e.g. a parent domain or a
  *   non-sandboxed process).
+ * - %LANDLOCK_SCOPED_SIGNAL: Restrict a sandboxed process from sending a signal
+ *   to another process outside sandbox domain.
  */
 /* clang-format off */
 #define LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET		(1ULL << 0)
+#define LANDLOCK_SCOPED_SIGNAL		                (1ULL << 1)
 /* clang-format on*/
 #endif /* _UAPI_LINUX_LANDLOCK_H */
diff --git a/security/landlock/limits.h b/security/landlock/limits.h
index eb01d0fb2165..fa28f9236407 100644
--- a/security/landlock/limits.h
+++ b/security/landlock/limits.h
@@ -26,7 +26,7 @@
 #define LANDLOCK_MASK_ACCESS_NET	((LANDLOCK_LAST_ACCESS_NET << 1) - 1)
 #define LANDLOCK_NUM_ACCESS_NET		__const_hweight64(LANDLOCK_MASK_ACCESS_NET)
 
-#define LANDLOCK_LAST_SCOPE		LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET
+#define LANDLOCK_LAST_SCOPE		LANDLOCK_SCOPED_SIGNAL
 #define LANDLOCK_MASK_SCOPE		((LANDLOCK_LAST_SCOPE << 1) - 1)
 #define LANDLOCK_NUM_SCOPE		__const_hweight64(LANDLOCK_MASK_SCOPE)
 /* clang-format on */
diff --git a/security/landlock/task.c b/security/landlock/task.c
index a461923c0571..9de96a5005c4 100644
--- a/security/landlock/task.c
+++ b/security/landlock/task.c
@@ -235,11 +235,38 @@ static int hook_unix_may_send(struct socket *const sock,
 	return 0;
 }
 
+static int hook_task_kill(struct task_struct *const p,
+			  struct kernel_siginfo *const info, const int sig,
+			  const struct cred *const cred)
+{
+	bool is_scoped;
+	const struct landlock_ruleset *target_dom, *dom;
+
+	dom = landlock_get_current_domain();
+	rcu_read_lock();
+	target_dom = landlock_get_task_domain(p);
+	if (cred)
+		/* dealing with USB IO */
+		is_scoped = domain_is_scoped(landlock_cred(cred)->domain,
+					     target_dom,
+					     LANDLOCK_SCOPED_SIGNAL);
+	else
+		is_scoped = (!dom) ? false :
+				     domain_is_scoped(dom, target_dom,
+						      LANDLOCK_SCOPED_SIGNAL);
+	rcu_read_unlock();
+	if (is_scoped)
+		return -EPERM;
+
+	return 0;
+}
+
 static struct security_hook_list landlock_hooks[] __ro_after_init = {
 	LSM_HOOK_INIT(ptrace_access_check, hook_ptrace_access_check),
 	LSM_HOOK_INIT(ptrace_traceme, hook_ptrace_traceme),
 	LSM_HOOK_INIT(unix_stream_connect, hook_unix_stream_connect),
 	LSM_HOOK_INIT(unix_may_send, hook_unix_may_send),
+	LSM_HOOK_INIT(task_kill, hook_task_kill),
 };
 
 __init void landlock_add_task_hooks(void)
-- 
2.34.1