Improve seccomp disable && Add locking to protect cred modifications in escape_to_root (tiann#2320)

- When disabling Seccomp, ensure that current->sighand->siglock is held
during the operation.
- Locking to ensure safe access and modification of the `cred` structure
within the `escape_to_root` function.

---

I think this issue described in tiann#2236 may have been caused by concurrent
read-write access without proper locking.

---------

Signed-off-by: SsageParuders<[email protected]>
Signed-off-by: SsageParuders <[email protected]>"

Author: SsageParuders

kernel/core_hook.c

@@ -110,14 +110,38 @@ static void setup_groups(struct root_profile *profile, struct cred *cred)
 	set_groups(cred, group_info);
 }
 
+static void disable_seccomp()
+{
+	assert_spin_locked(&current->sighand->siglock);
+	// disable seccomp
+#if defined(CONFIG_GENERIC_ENTRY) &&                                           \
+	LINUX_VERSION_CODE >= KERNEL_VERSION(5, 11, 0)
+	current_thread_info()->syscall_work &= ~SYSCALL_WORK_SECCOMP;
+#else
+	current_thread_info()->flags &= ~(TIF_SECCOMP | _TIF_SECCOMP);
+#endif
+
+#ifdef CONFIG_SECCOMP
+	current->seccomp.mode = 0;
+	current->seccomp.filter = NULL;
+#else
+#endif
+}
+
 void escape_to_root(void)
 {
 	struct cred *cred;
 
-	cred = (struct cred *)__task_cred(current);
+	rcu_read_lock();
+
+	do {
+		cred = (struct cred *)__task_cred((current));
+		BUG_ON(!cred);
+	} while (!get_cred_rcu(cred));
 
 	if (cred->euid.val == 0) {
 		pr_warn("Already root, don't escape!\n");
+		rcu_read_unlock();
 		return;
 	}
 	struct root_profile *profile = ksu_get_root_profile(cred->uid.val);
@@ -151,21 +175,15 @@ void escape_to_root(void)
 	memcpy(&cred->cap_ambient, &profile->capabilities.effective,
 	       sizeof(cred->cap_ambient));
 
-	// disable seccomp
-#if defined(CONFIG_GENERIC_ENTRY) &&                                           \
-	LINUX_VERSION_CODE >= KERNEL_VERSION(5, 11, 0)
-	current_thread_info()->syscall_work &= ~SYSCALL_WORK_SECCOMP;
-#else
-	current_thread_info()->flags &= ~(TIF_SECCOMP | _TIF_SECCOMP);
-#endif
+	setup_groups(profile, cred);
 
-#ifdef CONFIG_SECCOMP
-	current->seccomp.mode = 0;
-	current->seccomp.filter = NULL;
-#else
-#endif
+	rcu_read_unlock();
 
-	setup_groups(profile, cred);
+	// Refer to kernel/seccomp.c: seccomp_set_mode_strict
+	// When disabling Seccomp, ensure that current->sighand->siglock is held during the operation.
+	spin_lock_irq(&current->sighand->siglock);
+	disable_seccomp();
+	spin_unlock_irq(&current->sighand->siglock);
 
 	setup_selinux(profile->selinux_domain);
 }