[PATCH v7 19/28] fanotify: Limit number of marks with FAN_FS_ERROR per group

[Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>]

Since FAN_FS_ERROR memory must be pre-allocated, limit a single group
from watching too many file systems at once.  The current scheme
guarantees 1 slot per filesystem, so limit the number of marks with
FAN_FS_ERROR per group.

Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
---
 fs/notify/fanotify/fanotify_user.c | 10 ++++++++++
 include/linux/fsnotify_backend.h   |  1 +
 2 files changed, 11 insertions(+)

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index f1cf863d6f9f..5324890500fc 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -959,6 +959,10 @@ static int fanotify_remove_mark(struct fsnotify_group *group,
 
 	removed = fanotify_mark_remove_from_mask(fsn_mark, mask, flags,
 						 umask, &destroy_mark);
+
+	if (removed & FAN_FS_ERROR)
+		group->fanotify_data.error_event_marks--;
+
 	if (removed & fsnotify_conn_mask(fsn_mark->connector))
 		fsnotify_recalc_mask(fsn_mark->connector);
 	if (destroy_mark)
@@ -1057,6 +1061,9 @@ static struct fsnotify_mark *fanotify_add_new_mark(struct fsnotify_group *group,
 
 static int fanotify_group_init_error_pool(struct fsnotify_group *group)
 {
+	if (group->fanotify_data.error_event_marks >= FANOTIFY_DEFAULT_FEE_POOL)
+		return -ENOMEM;
+
 	if (mempool_initialized(&group->fanotify_data.error_events_pool))
 		return 0;
 
@@ -1098,6 +1105,9 @@ static int fanotify_add_mark(struct fsnotify_group *group,
 	if (added & ~fsnotify_conn_mask(fsn_mark->connector))
 		fsnotify_recalc_mask(fsn_mark->connector);
 
+	if (!(flags & FAN_MARK_IGNORED_MASK) && (mask & FAN_FS_ERROR))
+		group->fanotify_data.error_event_marks++;
+
 out:
 	mutex_unlock(&group->mark_mutex);
 
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 9941c06b8c8a..96e1d31394ce 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -247,6 +247,7 @@ struct fsnotify_group {
 			int f_flags; /* event_f_flags from fanotify_init() */
 			struct ucounts *ucounts;
 			mempool_t error_events_pool;
+			unsigned int error_event_marks;
 		} fanotify_data;
 #endif /* CONFIG_FANOTIFY */
 	};
-- 
2.33.0