Merge branch 'next-seccomp' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security

Pull seccomp updates from James Morris:
"Add support for retrieving seccomp metadata"

* 'next-seccomp' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security:
ptrace, seccomp: add support for retrieving seccomp metadata
seccomp: hoist out filter resolving logic

include/linux/seccomp.h

···
 #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE)
 extern long seccomp_get_filter(struct task_struct *task,
 			       unsigned long filter_off, void __user *data);
+extern long seccomp_get_metadata(struct task_struct *task,
+				 unsigned long filter_off, void __user *data);
 #else
 static inline long seccomp_get_filter(struct task_struct *task,
 				      unsigned long n, void __user *data)
+{
+	return -EINVAL;
+}
+static inline long seccomp_get_metadata(struct task_struct *task,
+					unsigned long filter_off,
+					void __user *data)
 {
 	return -EINVAL;
 }

include/uapi/linux/ptrace.h

···
 #define PTRACE_SETSIGMASK	0x420b
 
 #define PTRACE_SECCOMP_GET_FILTER	0x420c
+#define PTRACE_SECCOMP_GET_METADATA	0x420d
+
+struct seccomp_metadata {
+	unsigned long filter_off;	/* Input: which filter */
+	unsigned int flags;		/* Output: filter's flags */
+};
 
 /* Read signals from a shared (process wide) queue */
 #define PTRACE_PEEKSIGINFO_SHARED	(1 << 0)

kernel/ptrace.c

···
 		ret = seccomp_get_filter(child, addr, datavp);
 		break;
 
+	case PTRACE_SECCOMP_GET_METADATA:
+		ret = seccomp_get_metadata(child, addr, datavp);
+		break;
+
 	default:
 		break;
 	}

kernel/seccomp.c

···
 }
 
 #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE)
+static struct seccomp_filter *get_nth_filter(struct task_struct *task,
+					     unsigned long filter_off)
+{
+	struct seccomp_filter *orig, *filter;
+	unsigned long count;
+
+	/*
+	 * Note: this is only correct because the caller should be the (ptrace)
+	 * tracer of the task, otherwise lock_task_sighand is needed.
+	 */
+	spin_lock_irq(&task->sighand->siglock);
+
+	if (task->seccomp.mode != SECCOMP_MODE_FILTER) {
+		spin_unlock_irq(&task->sighand->siglock);
+		return ERR_PTR(-EINVAL);
+	}
+
+	orig = task->seccomp.filter;
+	__get_seccomp_filter(orig);
+	spin_unlock_irq(&task->sighand->siglock);
+
+	count = 0;
+	for (filter = orig; filter; filter = filter->prev)
+		count++;
+
+	if (filter_off >= count) {
+		filter = ERR_PTR(-ENOENT);
+		goto out;
+	}
+
+	count -= filter_off;
+	for (filter = orig; filter && count > 1; filter = filter->prev)
+		count--;
+
+	if (WARN_ON(count != 1 || !filter)) {
+		filter = ERR_PTR(-ENOENT);
+		goto out;
+	}
+
+	__get_seccomp_filter(filter);
+
+out:
+	__put_seccomp_filter(orig);
+	return filter;
+}
+
 long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
 			void __user *data)
 {
 	struct seccomp_filter *filter;
 	struct sock_fprog_kern *fprog;
 	long ret;
-	unsigned long count = 0;
 
 	if (!capable(CAP_SYS_ADMIN) ||
 	    current->seccomp.mode != SECCOMP_MODE_DISABLED) {
 		return -EACCES;
 	}
 
-	spin_lock_irq(&task->sighand->siglock);
-	if (task->seccomp.mode != SECCOMP_MODE_FILTER) {
-		ret = -EINVAL;
-		goto out;
-	}
-
-	filter = task->seccomp.filter;
-	while (filter) {
-		filter = filter->prev;
-		count++;
-	}
-
-	if (filter_off >= count) {
-		ret = -ENOENT;
-		goto out;
-	}
-	count -= filter_off;
-
-	filter = task->seccomp.filter;
-	while (filter && count > 1) {
-		filter = filter->prev;
-		count--;
-	}
-
-	if (WARN_ON(count != 1 || !filter)) {
-		/* The filter tree shouldn't shrink while we're using it. */
-		ret = -ENOENT;
-		goto out;
-	}
+	filter = get_nth_filter(task, filter_off);
+	if (IS_ERR(filter))
+		return PTR_ERR(filter);
 
 	fprog = filter->prog->orig_prog;
 	if (!fprog) {
···
 	if (!data)
 		goto out;
 
-	__get_seccomp_filter(filter);
-	spin_unlock_irq(&task->sighand->siglock);
-
 	if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog)))
 		ret = -EFAULT;
 
+out:
 	__put_seccomp_filter(filter);
 	return ret;
+}
 
-out:
-	spin_unlock_irq(&task->sighand->siglock);
+long seccomp_get_metadata(struct task_struct *task,
+			  unsigned long size, void __user *data)
+{
+	long ret;
+	struct seccomp_filter *filter;
+	struct seccomp_metadata kmd = {};
+
+	if (!capable(CAP_SYS_ADMIN) ||
+	    current->seccomp.mode != SECCOMP_MODE_DISABLED) {
+		return -EACCES;
+	}
+
+	size = min_t(unsigned long, size, sizeof(kmd));
+
+	if (copy_from_user(&kmd, data, size))
+		return -EFAULT;
+
+	filter = get_nth_filter(task, kmd.filter_off);
+	if (IS_ERR(filter))
+		return PTR_ERR(filter);
+
+	memset(&kmd, 0, sizeof(kmd));
+	if (filter->log)
+		kmd.flags |= SECCOMP_FILTER_FLAG_LOG;
+
+	ret = size;
+	if (copy_to_user(data, &kmd, size))
+		ret = -EFAULT;
+
+	__put_seccomp_filter(filter);
 	return ret;
 }
 #endif