[PATCH v2] landlock: Add abstract unix socket connect restrictions

[TaheraFahimi]

Abstract unix sockets are used for local interprocess communication without
relying on filesystem. Since landlock has no restriction for connecting to
a UNIX socket in the abstract namespace, a sandboxed process can connect to
a socket outside the sandboxed environment. Access to such sockets should
be scoped the same way ptrace access is limited.

For a landlocked process to be allowed to connect to a target process, it
must have a subset of the target process’s rules (the connecting socket
must be in a sub-domain of the listening socket). This patch adds a new
LSM hook for connect function in unix socket with the related access rights.

Link to first draft:
	https://lore.kernel.org/outreachy/20240328.ShoR4Iecei8o@digikod.net/

Signed-off-by: Tahera Fahimi <fahimitahera at gmail.com>

----
Changes in v2:
- Remove wrapper functions, noted by Casey Schaufler <casey at schaufler-ca.com>
---
 security/landlock/task.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/security/landlock/task.c b/security/landlock/task.c
index 849f5123610b..67528f87b7de 100644
--- a/security/landlock/task.c
+++ b/security/landlock/task.c
@@ -13,6 +13,7 @@
 #include <linux/lsm_hooks.h>
 #include <linux/rcupdate.h>
 #include <linux/sched.h>
+#include <net/sock.h>
 
 #include "common.h"
 #include "cred.h"
@@ -108,9 +109,48 @@ static int hook_ptrace_traceme(struct task_struct *const parent)
 	return task_ptrace(parent, current);
 }
 
+static bool unix_sock_is_scoped(struct sock *const sock,
+				struct sock *const other)
+{
+	bool is_scoped = true;
+
+	/* get the ruleset of connecting sock*/
+	const struct landlock_ruleset *const dom_sock =
+		landlock_get_current_domain();
+
+	if (!dom_sock)
+		return true;
+
+	/* get credential of listening sock*/
+	const struct cred *cred_other = get_cred(other->sk_peer_cred);
+
+	if (!cred_other)
+		return true;
+
+	/* retrieve the landlock_rulesets */
+	const struct landlock_ruleset *dom_parent;
+
+	rcu_read_lock();
+	dom_parent = landlock_cred(cred_other)->domain;
+	is_scoped = domain_scope_le(dom_parent, dom_sock);
+	rcu_read_unlock();
+
+	return is_scoped;
+}
+
+static int hook_unix_stream_connect(struct sock *const sock,
+				    struct sock *const other,
+				    struct sock *const newsk)
+{
+	if (unix_sock_is_scoped(sock, other))
+		return 0;
+	return -EPERM;
+}
+
 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),
 };
 
 __init void landlock_add_task_hooks(void)
-- 
2.34.1