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authorJan Kara <jack@suse.cz>2019-01-08 15:18:02 +0100
committerJan Kara <jack@suse.cz>2019-02-18 12:41:16 +0100
commitfabf7f29b3e2ce5ed9741bf06f3583cd7e82ed1c (patch)
treee835a20d5acb44c7a58cf5c279a638f5d60e24d5 /fs/notify
parent40873284d7106fc0f0f4d2deae74b38fb18342cc (diff)
downloadlinux-stericsson-fabf7f29b3e2ce5ed9741bf06f3583cd7e82ed1c.tar.gz
fanotify: Use interruptible wait when waiting for permission events
When waiting for response to fanotify permission events, we currently use uninterruptible waits. That makes code simple however it can cause lots of processes to end up in uninterruptible sleep with hard reboot being the only alternative in case fanotify listener process stops responding (e.g. due to a bug in its implementation). Uninterruptible sleep also makes system hibernation fail if the listener gets frozen before the process generating fanotify permission event. Fix these problems by using interruptible sleep for waiting for response to fanotify event. This is slightly tricky though - we have to detect when the event got already reported to userspace as in that case we must not free the event. Instead we push the responsibility for freeing the event to the process that will write response to the event. Reported-by: Orion Poplawski <orion@nwra.com> Reported-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Reviewed-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Jan Kara <jack@suse.cz>
Diffstat (limited to 'fs/notify')
-rw-r--r--fs/notify/fanotify/fanotify.c35
-rw-r--r--fs/notify/fanotify/fanotify.h3
-rw-r--r--fs/notify/fanotify/fanotify_user.c9
3 files changed, 42 insertions, 5 deletions
diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 812c975df7ec..ff7b8a1cdfe1 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -77,6 +77,13 @@ static int fanotify_merge(struct list_head *list, struct fsnotify_event *event)
return 0;
}
+/*
+ * Wait for response to permission event. The function also takes care of
+ * freeing the permission event (or offloads that in case the wait is canceled
+ * by a signal). The function returns 0 in case access got allowed by userspace,
+ * -EPERM in case userspace disallowed the access, and -ERESTARTSYS in case
+ * the wait got interrupted by a signal.
+ */
static int fanotify_get_response(struct fsnotify_group *group,
struct fanotify_perm_event *event,
struct fsnotify_iter_info *iter_info)
@@ -85,8 +92,29 @@ static int fanotify_get_response(struct fsnotify_group *group,
pr_debug("%s: group=%p event=%p\n", __func__, group, event);
- wait_event(group->fanotify_data.access_waitq,
- event->state == FAN_EVENT_ANSWERED);
+ ret = wait_event_interruptible(group->fanotify_data.access_waitq,
+ event->state == FAN_EVENT_ANSWERED);
+ /* Signal pending? */
+ if (ret < 0) {
+ spin_lock(&group->notification_lock);
+ /* Event reported to userspace and no answer yet? */
+ if (event->state == FAN_EVENT_REPORTED) {
+ /* Event will get freed once userspace answers to it */
+ event->state = FAN_EVENT_CANCELED;
+ spin_unlock(&group->notification_lock);
+ return ret;
+ }
+ /* Event not yet reported? Just remove it. */
+ if (event->state == FAN_EVENT_INIT)
+ fsnotify_remove_queued_event(group, &event->fae.fse);
+ /*
+ * Event may be also answered in case signal delivery raced
+ * with wakeup. In that case we have nothing to do besides
+ * freeing the event and reporting error.
+ */
+ spin_unlock(&group->notification_lock);
+ goto out;
+ }
/* userspace responded, convert to something usable */
switch (event->response & ~FAN_AUDIT) {
@@ -104,6 +132,8 @@ static int fanotify_get_response(struct fsnotify_group *group,
pr_debug("%s: group=%p event=%p about to return ret=%d\n", __func__,
group, event, ret);
+out:
+ fsnotify_destroy_event(group, &event->fae.fse);
return ret;
}
@@ -406,7 +436,6 @@ static int fanotify_handle_event(struct fsnotify_group *group,
} else if (fanotify_is_perm_event(mask)) {
ret = fanotify_get_response(group, FANOTIFY_PE(fsn_event),
iter_info);
- fsnotify_destroy_event(group, fsn_event);
}
finish:
if (fanotify_is_perm_event(mask))
diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
index 480f281996d4..68b30504284c 100644
--- a/fs/notify/fanotify/fanotify.h
+++ b/fs/notify/fanotify/fanotify.h
@@ -12,7 +12,8 @@ extern struct kmem_cache *fanotify_perm_event_cachep;
enum {
FAN_EVENT_INIT,
FAN_EVENT_REPORTED,
- FAN_EVENT_ANSWERED
+ FAN_EVENT_ANSWERED,
+ FAN_EVENT_CANCELED,
};
/*
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 3c272f61d341..56992b32c6bb 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -147,10 +147,17 @@ static void finish_permission_event(struct fsnotify_group *group,
unsigned int response)
__releases(&group->notification_lock)
{
+ bool destroy = false;
+
assert_spin_locked(&group->notification_lock);
event->response = response;
- event->state = FAN_EVENT_ANSWERED;
+ if (event->state == FAN_EVENT_CANCELED)
+ destroy = true;
+ else
+ event->state = FAN_EVENT_ANSWERED;
spin_unlock(&group->notification_lock);
+ if (destroy)
+ fsnotify_destroy_event(group, &event->fae.fse);
}
static int process_access_response(struct fsnotify_group *group,