Message-Id: <20210521024134.1032503-9-krisman@collabora.com>
Date:   Thu, 20 May 2021 22:41:31 -0400
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     amir73il@...il.com
Cc:     Gabriel Krisman Bertazi <krisman@...labora.com>,
        kernel@...labora.com, "Darrick J . Wong" <djwong@...nel.org>,
        Theodore Ts'o <tytso@....edu>,
        Dave Chinner <david@...morbit.com>, jack@...e.com,
        dhowells@...hat.com, khazhy@...gle.com,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: [PATCH 08/11] fanotify: Introduce FAN_ERROR event

The FAN_ERROR event is used by filesystem wide monitoring tools to
receive notifications of type FS_ERROR_EVENT, emited by filesystems when
a problem is detected.  The error notification includes a generic error
descriptor.

Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>

Changes since v1:
  - Pass dentry to fanotify_check_fsid (Amir)
  - FANOTIFY_EVENT_TYPE_ERROR -> FANOTIFY_EVENT_TYPE_FS_ERROR
  - Merge previous patch into it
  - Use a single slot
---
 fs/notify/fanotify/fanotify.c      |  74 ++++++++++++++++-
 fs/notify/fanotify/fanotify.h      |  28 ++++++-
 fs/notify/fanotify/fanotify_user.c | 123 ++++++++++++++++++++++++++---
 include/linux/fanotify.h           |   6 +-
 include/uapi/linux/fanotify.h      |  10 +++
 5 files changed, 225 insertions(+), 16 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 34e2ee759b39..197291a8c41d 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -269,7 +269,7 @@ static u32 fanotify_group_event_mask(struct fsnotify_group *group,
 	pr_debug("%s: report_mask=%x mask=%x data=%p data_type=%d\n",
 		 __func__, iter_info->report_mask, event_mask, data, data_type);
 
-	if (!fid_mode) {
+	if (!fid_mode && data_type != FSNOTIFY_EVENT_ERROR) {
 		/* Do we have path to open a file descriptor? */
 		if (!path)
 			return 0;
@@ -657,6 +657,51 @@ static struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
 	return event;
 }
 
+static void fanotify_init_error_event(struct fanotify_error_event *event,
+				      __kernel_fsid_t fsid,
+				      const struct fs_error_report *report)
+{
+	event->fae.type = FANOTIFY_EVENT_TYPE_FS_ERROR;
+	event->err_count = 1;
+	event->fsid = fsid;
+	event->error = report->error;
+	event->ino = (report->inode) ? report->inode->i_ino : 0;
+}
+
+static int fanotify_queue_error_event(struct fsnotify_iter_info *iter_info,
+				      struct fsnotify_group *group,
+				      __kernel_fsid_t fsid,
+				      const struct fs_error_report *report)
+{
+	struct fanotify_mark *mark;
+	int type;
+	int ret = -ENOMEM;
+
+	fsnotify_foreach_obj_type(type) {
+		if (!fsnotify_iter_should_report_type(iter_info, type))
+			continue;
+		mark = FANOTIFY_MARK(iter_info->marks[type]);
+	}
+
+	spin_lock(&mark->fsn_mark.lock);
+	if (mark->error_event) {
+		if (list_empty(&mark->error_event->fae.fse.list)) {
+			fsnotify_get_mark(&mark->fsn_mark);
+			fanotify_init_error_event(mark->error_event, fsid, report);
+			ret = fsnotify_add_event(group, &mark->error_event->fae.fse,
+						 NULL, NULL);
+			if (ret)
+				fsnotify_put_mark(&mark->fsn_mark);
+		} else {
+			mark->error_event->err_count++;
+			ret = 0;
+		}
+	}
+	spin_unlock(&mark->fsn_mark.lock);
+
+	return ret;
+}
+
 /*
  * Get cached fsid of the filesystem containing the object from any connector.
  * All connectors are supposed to have the same fsid, but we do not verify that
@@ -738,8 +783,9 @@ static int fanotify_handle_event(struct fsnotify_group *group, u32 mask,
 	BUILD_BUG_ON(FAN_ONDIR != FS_ISDIR);
 	BUILD_BUG_ON(FAN_OPEN_EXEC != FS_OPEN_EXEC);
 	BUILD_BUG_ON(FAN_OPEN_EXEC_PERM != FS_OPEN_EXEC_PERM);
+	BUILD_BUG_ON(FAN_ERROR != FS_ERROR);
 
-	BUILD_BUG_ON(HWEIGHT32(ALL_FANOTIFY_EVENT_BITS) != 19);
+	BUILD_BUG_ON(HWEIGHT32(ALL_FANOTIFY_EVENT_BITS) != 20);
 
 	mask = fanotify_group_event_mask(group, iter_info, mask, data,
 					 data_type, dir);
@@ -757,13 +803,20 @@ static int fanotify_handle_event(struct fsnotify_group *group, u32 mask,
 			return 0;
 	}
 
-	if (FAN_GROUP_FLAG(group, FANOTIFY_FID_BITS)) {
+	if (FAN_GROUP_FLAG(group, FANOTIFY_FID_BITS) || fanotify_is_error_event(mask)) {
 		fsid = fanotify_get_fsid(iter_info);
 		/* Racing with mark destruction or creation? */
 		if (!fsid.val[0] && !fsid.val[1])
 			return 0;
 	}
 
+	if (fanotify_is_error_event(mask)) {
+		ret = fanotify_queue_error_event(iter_info, group, fsid, data);
+		if (ret)
+			fsnotify_queue_overflow(group);
+		goto finish;
+	}
+
 	event = fanotify_alloc_event(group, mask, data, data_type, dir,
 				     file_name, &fsid);
 	ret = -ENOMEM;
@@ -833,6 +886,17 @@ static void fanotify_free_name_event(struct fanotify_event *event)
 	kfree(FANOTIFY_NE(event));
 }
 
+static void fanotify_free_error_event(struct fanotify_event *event)
+{
+	/*
+	 * Just drop the reference acquired by
+	 * fanotify_queue_error_event.
+	 *
+	 * The actual memory is freed with the mark.
+	 */
+	fsnotify_put_mark(&(FANOTIFY_EE(event)->mark->fsn_mark));
+}
+
 static void fanotify_free_event(struct fsnotify_event *fsn_event)
 {
 	struct fanotify_event *event;
@@ -855,6 +919,9 @@ static void fanotify_free_event(struct fsnotify_event *fsn_event)
 	case FANOTIFY_EVENT_TYPE_OVERFLOW:
 		kfree(event);
 		break;
+	case FANOTIFY_EVENT_TYPE_FS_ERROR:
+		fanotify_free_error_event(event);
+		break;
 	default:
 		WARN_ON_ONCE(1);
 	}
@@ -871,6 +938,7 @@ static void fanotify_free_mark(struct fsnotify_mark *fsn_mark)
 {
 	struct fanotify_mark *mark = FANOTIFY_MARK(fsn_mark);
 
+	kfree(mark->error_event);
 	kmem_cache_free(fanotify_mark_cache, mark);
 }
 
diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
index a399c5e2615d..ebe9e593dfbf 100644
--- a/fs/notify/fanotify/fanotify.h
+++ b/fs/notify/fanotify/fanotify.h
@@ -151,6 +151,7 @@ enum fanotify_event_type {
 	FANOTIFY_EVENT_TYPE_PATH,
 	FANOTIFY_EVENT_TYPE_PATH_PERM,
 	FANOTIFY_EVENT_TYPE_OVERFLOW, /* struct fanotify_event */
+	FANOTIFY_EVENT_TYPE_FS_ERROR, /* struct fanotify_error_event */
 	__FANOTIFY_EVENT_TYPE_NUM
 };
 
@@ -206,12 +207,31 @@ FANOTIFY_NE(struct fanotify_event *event)
 	return container_of(event, struct fanotify_name_event, fae);
 }
 
+struct fanotify_error_event {
+	struct fanotify_event fae;
+	__kernel_fsid_t fsid;
+	unsigned long ino;
+	int error;
+	u32 err_count;
+
+	/* Back reference to the mark this error refers to. */
+	struct fanotify_mark *mark;
+};
+
+static inline struct fanotify_error_event *
+FANOTIFY_EE(struct fanotify_event *event)
+{
+	return container_of(event, struct fanotify_error_event, fae);
+}
+
 static inline __kernel_fsid_t *fanotify_event_fsid(struct fanotify_event *event)
 {
 	if (event->type == FANOTIFY_EVENT_TYPE_FID)
 		return &FANOTIFY_FE(event)->fsid;
 	else if (event->type == FANOTIFY_EVENT_TYPE_FID_NAME)
 		return &FANOTIFY_NE(event)->fsid;
+	else if (event->type == FANOTIFY_EVENT_TYPE_FS_ERROR)
+		return &FANOTIFY_EE(event)->fsid;
 	else
 		return NULL;
 }
@@ -297,6 +317,11 @@ static inline struct fanotify_event *FANOTIFY_E(struct fsnotify_event *fse)
 	return container_of(fse, struct fanotify_event, fse);
 }
 
+static inline bool fanotify_is_error_event(u32 mask)
+{
+	return mask & FANOTIFY_ERROR_EVENTS;
+}
+
 static inline bool fanotify_event_has_path(struct fanotify_event *event)
 {
 	return event->type == FANOTIFY_EVENT_TYPE_PATH ||
@@ -325,7 +350,8 @@ static inline struct path *fanotify_event_path(struct fanotify_event *event)
  */
 static inline bool fanotify_is_hashed_event(u32 mask)
 {
-	return !fanotify_is_perm_event(mask) && !(mask & FS_Q_OVERFLOW);
+	return (!fanotify_is_perm_event(mask) && !fanotify_is_error_event(mask)
+		&& !(mask & FS_Q_OVERFLOW));
 }
 
 static inline unsigned int fanotify_event_hash_bucket(
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 00210535a78e..ea9b9f8f7c21 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -106,6 +106,8 @@ struct kmem_cache *fanotify_perm_event_cachep __read_mostly;
 #define FANOTIFY_EVENT_ALIGN 4
 #define FANOTIFY_INFO_HDR_LEN \
 	(sizeof(struct fanotify_event_info_fid) + sizeof(struct file_handle))
+#define FANOTIFY_INFO_ERROR_LEN \
+	(sizeof(struct fanotify_event_info_error))
 
 static int fanotify_fid_info_len(int fh_len, int name_len)
 {
@@ -126,6 +128,9 @@ static size_t fanotify_event_len(struct fanotify_event *event,
 	int fh_len;
 	int dot_len = 0;
 
+	if (fanotify_is_error_event(event->mask))
+		return event_len + FANOTIFY_INFO_ERROR_LEN;
+
 	if (!fid_mode)
 		return event_len;
 
@@ -149,6 +154,30 @@ static size_t fanotify_event_len(struct fanotify_event *event,
 	return event_len;
 }
 
+static struct fanotify_event *fanotify_dequeue_error_event(struct fsnotify_group *group,
+							   struct fanotify_event *event,
+							   struct fanotify_error_event *error_event)
+{
+	struct fsnotify_mark *mark = &(FANOTIFY_EE(event)->mark->fsn_mark);
+	/*
+	 * In order to avoid missing an error count update, the
+	 * queued event is de-queued and duplicated to an
+	 * in-stack fanotify_error_event while still inside
+	 * mark->lock.  Once the event is dequeued, it can be
+	 * immediately re-used for a new event.
+	 *
+	 * The ownership of the mark reference is dropped later
+	 * by destroy_event.
+	 */
+	spin_lock(&mark->lock);
+	memcpy(error_event, FANOTIFY_EE(event), sizeof(*error_event));
+	fsnotify_init_event(&error_event->fae.fse);
+	fsnotify_remove_queued_event(group, &event->fse);
+	spin_unlock(&mark->lock);
+
+	return &error_event->fae;
+}
+
 /*
  * Remove an hashed event from merge hash table.
  */
@@ -173,7 +202,8 @@ static void fanotify_unhash_event(struct fsnotify_group *group,
  * updated accordingly.
  */
 static struct fanotify_event *get_one_event(struct fsnotify_group *group,
-					    size_t count)
+					    size_t count,
+					    struct fanotify_error_event *error_event)
 {
 	size_t event_size;
 	struct fanotify_event *event = NULL;
@@ -197,9 +227,14 @@ static struct fanotify_event *get_one_event(struct fsnotify_group *group,
 
 	/*
 	 * Held the notification_lock the whole time, so this is the
-	 * same event we peeked above.
+	 * same event we peeked above, unless it is copied to
+	 * error_event.
 	 */
-	fsnotify_remove_first_event(group);
+	if (fanotify_is_error_event(event->mask))
+		event = fanotify_dequeue_error_event(group, event, error_event);
+	else
+		fsnotify_remove_first_event(group);
+
 	if (fanotify_is_perm_event(event->mask))
 		FANOTIFY_PERM(event)->state = FAN_EVENT_REPORTED;
 	if (fanotify_is_hashed_event(event->mask))
@@ -309,6 +344,30 @@ static int process_access_response(struct fsnotify_group *group,
 	return -ENOENT;
 }
 
+static size_t copy_error_info_to_user(struct fanotify_event *event,
+				      char __user *buf, int count)
+{
+	struct fanotify_event_info_error info;
+	struct fanotify_error_event *fee = FANOTIFY_EE(event);
+
+	info.hdr.info_type = FAN_EVENT_INFO_TYPE_ERROR;
+	info.hdr.pad = 0;
+	info.hdr.len = sizeof(struct fanotify_event_info_error);
+
+	if (WARN_ON(count < info.hdr.len))
+		return -EFAULT;
+
+	info.fsid = fee->fsid;
+	info.error = fee->error;
+	info.inode = fee->ino;
+	info.error_count = fee->err_count;
+
+	if (copy_to_user(buf, &info, sizeof(info)))
+		return -EFAULT;
+
+	return info.hdr.len;
+}
+
 static int copy_info_to_user(__kernel_fsid_t *fsid, struct fanotify_fh *fh,
 			     int info_type, const char *name, size_t name_len,
 			     char __user *buf, size_t count)
@@ -523,6 +582,14 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
 		count -= ret;
 	}
 
+	if (fanotify_is_error_event(event->mask)) {
+		ret = copy_error_info_to_user(event, buf, count);
+		if (ret < 0)
+			return ret;
+		buf += ret;
+		count -= ret;
+	}
+
 	return metadata.event_len;
 
 out_close_fd:
@@ -553,6 +620,7 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
 {
 	struct fsnotify_group *group;
 	struct fanotify_event *event;
+	struct fanotify_error_event error_event;
 	char __user *start;
 	int ret;
 	DEFINE_WAIT_FUNC(wait, woken_wake_function);
@@ -569,7 +637,7 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
 		 * in case there are lots of available events.
 		 */
 		cond_resched();
-		event = get_one_event(group, count);
+		event = get_one_event(group, count, &error_event);
 		if (IS_ERR(event)) {
 			ret = PTR_ERR(event);
 			break;
@@ -888,16 +956,33 @@ static int fanotify_remove_inode_mark(struct fsnotify_group *group,
 				    flags, umask);
 }
 
-static __u32 fanotify_mark_add_to_mask(struct fsnotify_mark *fsn_mark,
-				       __u32 mask,
-				       unsigned int flags)
+static int fanotify_mark_add_to_mask(struct fsnotify_mark *fsn_mark,
+				       __u32 mask, unsigned int flags,
+				     __u32 *modified_mask)
 {
+	struct fanotify_mark *mark = FANOTIFY_MARK(fsn_mark);
+	struct fanotify_error_event *error_event = NULL;
+	bool addition = !(flags & FAN_MARK_IGNORED_MASK);
 	__u32 oldmask = -1;
 
+	/* Only pre-alloc error_event if needed. */
+	if (addition && (mask & FAN_ERROR) && !mark->error_event) {
+		error_event = kzalloc(sizeof(*error_event), GFP_KERNEL);
+		if (!error_event)
+			return -ENOMEM;
+		fanotify_init_event(&error_event->fae, 0, FS_ERROR);
+		error_event->mark = mark;
+	}
+
 	spin_lock(&fsn_mark->lock);
-	if (!(flags & FAN_MARK_IGNORED_MASK)) {
+	if (addition) {
 		oldmask = fsn_mark->mask;
 		fsn_mark->mask |= mask;
+
+		if (!mark->error_event) {
+			mark->error_event = error_event;
+			error_event = NULL;
+		}
 	} else {
 		fsn_mark->ignored_mask |= mask;
 		if (flags & FAN_MARK_IGNORED_SURV_MODIFY)
@@ -905,7 +990,11 @@ static __u32 fanotify_mark_add_to_mask(struct fsnotify_mark *fsn_mark,
 	}
 	spin_unlock(&fsn_mark->lock);
 
-	return mask & ~oldmask;
+	kfree(error_event);
+
+	*modified_mask = mask & ~oldmask;
+	return 0;
+
 }
 
 static struct fsnotify_mark *fanotify_add_new_mark(struct fsnotify_group *group,
@@ -955,6 +1044,7 @@ static int fanotify_add_mark(struct fsnotify_group *group,
 {
 	struct fsnotify_mark *fsn_mark;
 	__u32 added;
+	int ret = 0;
 
 	mutex_lock(&group->mark_mutex);
 	fsn_mark = fsnotify_find_mark(connp, group);
@@ -965,13 +1055,18 @@ static int fanotify_add_mark(struct fsnotify_group *group,
 			return PTR_ERR(fsn_mark);
 		}
 	}
-	added = fanotify_mark_add_to_mask(fsn_mark, mask, flags);
+	ret = fanotify_mark_add_to_mask(fsn_mark, mask, flags, &added);
+	if (ret)
+		goto out;
+
 	if (added & ~fsnotify_conn_mask(fsn_mark->connector))
 		fsnotify_recalc_mask(fsn_mark->connector);
+
+out:
 	mutex_unlock(&group->mark_mutex);
 
 	fsnotify_put_mark(fsn_mark);
-	return 0;
+	return ret;
 }
 
 static int fanotify_add_vfsmount_mark(struct fsnotify_group *group,
@@ -1377,6 +1472,12 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
 
 		fsid = &__fsid;
 	}
+	if (mask & FAN_ERROR) {
+		ret = fanotify_test_fsid(path.dentry, &__fsid);
+		if (ret)
+			goto path_put_and_out;
+		fsid = &__fsid;
+	}
 
 	/* inode held in place by reference to path; group by fget on fd */
 	if (mark_type == FAN_MARK_INODE)
diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
index bad41bcb25df..05c929d588e4 100644
--- a/include/linux/fanotify.h
+++ b/include/linux/fanotify.h
@@ -81,9 +81,12 @@ extern struct ctl_table fanotify_table[]; /* for sysctl */
 #define FANOTIFY_INODE_EVENTS	(FANOTIFY_DIRENT_EVENTS | \
 				 FAN_ATTRIB | FAN_MOVE_SELF | FAN_DELETE_SELF)
 
+#define FANOTIFY_ERROR_EVENTS	(FAN_ERROR)
+
 /* Events that user can request to be notified on */
 #define FANOTIFY_EVENTS		(FANOTIFY_PATH_EVENTS | \
-				 FANOTIFY_INODE_EVENTS)
+				 FANOTIFY_INODE_EVENTS | \
+				 FANOTIFY_ERROR_EVENTS)
 
 /* Events that require a permission response from user */
 #define FANOTIFY_PERM_EVENTS	(FAN_OPEN_PERM | FAN_ACCESS_PERM | \
@@ -95,6 +98,7 @@ extern struct ctl_table fanotify_table[]; /* for sysctl */
 /* Events that may be reported to user */
 #define FANOTIFY_OUTGOING_EVENTS	(FANOTIFY_EVENTS | \
 					 FANOTIFY_PERM_EVENTS | \
+					 FANOTIFY_ERROR_EVENTS | \
 					 FAN_Q_OVERFLOW | FAN_ONDIR)
 
 #define ALL_FANOTIFY_EVENT_BITS		(FANOTIFY_OUTGOING_EVENTS | \
diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
index fbf9c5c7dd59..e3920597112f 100644
--- a/include/uapi/linux/fanotify.h
+++ b/include/uapi/linux/fanotify.h
@@ -20,6 +20,7 @@
 #define FAN_OPEN_EXEC		0x00001000	/* File was opened for exec */
 
 #define FAN_Q_OVERFLOW		0x00004000	/* Event queued overflowed */
+#define FAN_ERROR		0x00008000	/* Filesystem error */
 
 #define FAN_OPEN_PERM		0x00010000	/* File open in perm check */
 #define FAN_ACCESS_PERM		0x00020000	/* File accessed in perm check */
@@ -123,6 +124,7 @@ struct fanotify_event_metadata {
 #define FAN_EVENT_INFO_TYPE_FID		1
 #define FAN_EVENT_INFO_TYPE_DFID_NAME	2
 #define FAN_EVENT_INFO_TYPE_DFID	3
+#define FAN_EVENT_INFO_TYPE_ERROR	4
 
 /* Variable length info record following event metadata */
 struct fanotify_event_info_header {
@@ -148,6 +150,14 @@ struct fanotify_event_info_fid {
 	unsigned char handle[0];
 };
 
+struct fanotify_event_info_error {
+	struct fanotify_event_info_header hdr;
+	int error;
+	__kernel_fsid_t fsid;
+	unsigned long inode;
+	__u32 error_count;
+};
+
 struct fanotify_response {
 	__s32 fd;
 	__u32 response;
-- 
2.31.0

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