fanotify: define struct members to hold response decision context

This patch adds a flag, FAN_INFO and an extensible buffer to provide
additional information about response decisions.  The buffer contains
one or more headers defining the information type and the length of the
following information.  The patch defines one additional information
type, FAN_RESPONSE_INFO_AUDIT_RULE, to audit a rule number.  This will
allow for the creation of other information types in the future if other
users of the API identify different needs.

The kernel can be tested if it supports a given info type by supplying
the complete info extension but setting fd to FAN_NOFD.  It will return
the expected size but not issue an audit record.

Suggested-by: Steve Grubb <sgrubb@redhat.com>
Link: https://lore.kernel.org/r/2745105.e9J7NaK4W3@x2
Suggested-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20201001101219.GE17860@quack2.suse.cz
Tested-by: Steve Grubb <sgrubb@redhat.com>
Acked-by: Steve Grubb <sgrubb@redhat.com>
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <10177cfcae5480926b7176321a28d9da6835b667.1675373475.git.rgb@redhat.com>

3 files changed, 73 insertions, 22 deletions

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index a2a15bc4df28..24ec1d66d5a8 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -262,7 +262,7 @@ static int fanotify_get_response(struct fsnotify_group *group,
 	}
 
 	/* userspace responded, convert to something usable */
-	switch (event->response & ~FAN_AUDIT) {
+	switch (event->response & FANOTIFY_RESPONSE_ACCESS) {
 	case FAN_ALLOW:
 		ret = 0;
 		break;
@@ -563,6 +563,9 @@ static struct fanotify_event *fanotify_alloc_perm_event(const struct path *path,
 
 	pevent->fae.type = FANOTIFY_EVENT_TYPE_PATH_PERM;
 	pevent->response = 0;
+	pevent->hdr.type = FAN_RESPONSE_INFO_NONE;
+	pevent->hdr.pad = 0;
+	pevent->hdr.len = 0;
 	pevent->state = FAN_EVENT_INIT;
 	pevent->path = *path;
 	path_get(path);
diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
index f899d610bc08..e8a3c28c5d12 100644
--- a/fs/notify/fanotify/fanotify.h
+++ b/fs/notify/fanotify/fanotify.h
@@ -428,6 +428,10 @@ struct fanotify_perm_event {
 	u32 response;			/* userspace answer to the event */
 	unsigned short state;		/* state of the event */
 	int fd;		/* fd we passed to userspace for this event */
+	union {
+		struct fanotify_response_info_header hdr;
+		struct fanotify_response_info_audit_rule audit_rule;
+	};
 };
 
 static inline struct fanotify_perm_event *
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index caa1211bac8c..8f430bfad487 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -283,19 +283,42 @@ static int create_fd(struct fsnotify_group *group, const struct path *path,
 	return client_fd;
 }
 
+static int process_access_response_info(const char __user *info,
+					size_t info_len,
+				struct fanotify_response_info_audit_rule *friar)
+{
+	if (info_len != sizeof(*friar))
+		return -EINVAL;
+
+	if (copy_from_user(friar, info, sizeof(*friar)))
+		return -EFAULT;
+
+	if (friar->hdr.type != FAN_RESPONSE_INFO_AUDIT_RULE)
+		return -EINVAL;
+	if (friar->hdr.pad != 0)
+		return -EINVAL;
+	if (friar->hdr.len != sizeof(*friar))
+		return -EINVAL;
+
+	return info_len;
+}
+
 /*
  * Finish processing of permission event by setting it to ANSWERED state and
  * drop group->notification_lock.
  */
 static void finish_permission_event(struct fsnotify_group *group,
-				    struct fanotify_perm_event *event,
-				    u32 response)
+				    struct fanotify_perm_event *event, u32 response,
+				    struct fanotify_response_info_audit_rule *friar)
 				    __releases(&group->notification_lock)
 {
 	bool destroy = false;
 
 	assert_spin_locked(&group->notification_lock);
-	event->response = response;
+	event->response = response & ~FAN_INFO;
+	if (response & FAN_INFO)
+		memcpy(&event->audit_rule, friar, sizeof(*friar));
+
 	if (event->state == FAN_EVENT_CANCELED)
 		destroy = true;
 	else
@@ -306,20 +329,27 @@ static void finish_permission_event(struct fsnotify_group *group,
 }
 
 static int process_access_response(struct fsnotify_group *group,
-				   struct fanotify_response *response_struct)
+				   struct fanotify_response *response_struct,
+				   const char __user *info,
+				   size_t info_len)
 {
 	struct fanotify_perm_event *event;
 	int fd = response_struct->fd;
 	u32 response = response_struct->response;
+	int ret = info_len;
+	struct fanotify_response_info_audit_rule friar;
 
-	pr_debug("%s: group=%p fd=%d response=%u\n", __func__, group,
-		 fd, response);
+	pr_debug("%s: group=%p fd=%d response=%u buf=%p size=%zu\n", __func__,
+		 group, fd, response, info, info_len);
 	/*
 	 * make sure the response is valid, if invalid we do nothing and either
 	 * userspace can send a valid response or we will clean it up after the
 	 * timeout
 	 */
-	switch (response & ~FAN_AUDIT) {
+	if (response & ~FANOTIFY_RESPONSE_VALID_MASK)
+		return -EINVAL;
+
+	switch (response & FANOTIFY_RESPONSE_ACCESS) {
 	case FAN_ALLOW:
 	case FAN_DENY:
 		break;
@@ -327,10 +357,20 @@ static int process_access_response(struct fsnotify_group *group,
 		return -EINVAL;
 	}
 
-	if (fd < 0)
+	if ((response & FAN_AUDIT) && !FAN_GROUP_FLAG(group, FAN_ENABLE_AUDIT))
 		return -EINVAL;
 
-	if ((response & FAN_AUDIT) && !FAN_GROUP_FLAG(group, FAN_ENABLE_AUDIT))
+	if (response & FAN_INFO) {
+		ret = process_access_response_info(info, info_len, &friar);
+		if (ret < 0)
+			return ret;
+		if (fd == FAN_NOFD)
+			return ret;
+	} else {
+		ret = 0;
+	}
+
+	if (fd < 0)
 		return -EINVAL;
 
 	spin_lock(&group->notification_lock);
@@ -340,9 +380,9 @@ static int process_access_response(struct fsnotify_group *group,
 			continue;
 
 		list_del_init(&event->fae.fse.list);
-		finish_permission_event(group, event, response);
+		finish_permission_event(group, event, response, &friar);
 		wake_up(&group->fanotify_data.access_waitq);
-		return 0;
+		return ret;
 	}
 	spin_unlock(&group->notification_lock);
 
@@ -804,7 +844,7 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
 			if (ret <= 0) {
 				spin_lock(&group->notification_lock);
 				finish_permission_event(group,
-					FANOTIFY_PERM(event), FAN_DENY);
+					FANOTIFY_PERM(event), FAN_DENY, NULL);
 				wake_up(&group->fanotify_data.access_waitq);
 			} else {
 				spin_lock(&group->notification_lock);
@@ -827,28 +867,32 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
 
 static ssize_t fanotify_write(struct file *file, const char __user *buf, size_t count, loff_t *pos)
 {
-	struct fanotify_response response = { .fd = -1, .response = -1 };
+	struct fanotify_response response;
 	struct fsnotify_group *group;
 	int ret;
+	const char __user *info_buf = buf + sizeof(struct fanotify_response);
+	size_t info_len;
 
 	if (!IS_ENABLED(CONFIG_FANOTIFY_ACCESS_PERMISSIONS))
 		return -EINVAL;
 
 	group = file->private_data;
 
+	pr_debug("%s: group=%p count=%zu\n", __func__, group, count);
+
 	if (count < sizeof(response))
 		return -EINVAL;
 
-	count = sizeof(response);
-
-	pr_debug("%s: group=%p count=%zu\n", __func__, group, count);
-
-	if (copy_from_user(&response, buf, count))
+	if (copy_from_user(&response, buf, sizeof(response)))
 		return -EFAULT;
 
-	ret = process_access_response(group, &response);
+	info_len = count - sizeof(response);
+
+	ret = process_access_response(group, &response, info_buf, info_len);
 	if (ret < 0)
 		count = ret;
+	else
+		count = sizeof(response) + ret;
 
 	return count;
 }
@@ -876,7 +920,7 @@ static int fanotify_release(struct inode *ignored, struct file *file)
 		event = list_first_entry(&group->fanotify_data.access_list,
 				struct fanotify_perm_event, fae.fse.list);
 		list_del_init(&event->fae.fse.list);
-		finish_permission_event(group, event, FAN_ALLOW);
+		finish_permission_event(group, event, FAN_ALLOW, NULL);
 		spin_lock(&group->notification_lock);
 	}
 
@@ -893,7 +937,7 @@ static int fanotify_release(struct inode *ignored, struct file *file)
 			fsnotify_destroy_event(group, fsn_event);
 		} else {
 			finish_permission_event(group, FANOTIFY_PERM(event),
-						FAN_ALLOW);
+						FAN_ALLOW, NULL);
 		}
 		spin_lock(&group->notification_lock);
 	}