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Subject[PATCH =-v3 13/21] fanotify: ability for userspace to delay responses
Date
Userspace may know that it is behind, may know it is going to take a while
to get a good response, or have any number of other reasons to block an
access request. FAN_RESTTIMER will reset the timeout for an fanotify
access decision response.

Signed-off-by: Eric Paris <eparis@redhat.com>
---
fs/notify/access.c | 31 +++++++++++++++++++++++++++----
fs/notify/fanotify.h | 1 +
fs/notify/notification.c | 2 ++
include/linux/fanotify.h | 1 +
4 files changed, 31 insertions(+), 4 deletions(-)
diff --git a/fs/notify/access.c b/fs/notify/access.c
index 6a2606c..5b3b32e 100644
--- a/fs/notify/access.c
+++ b/fs/notify/access.c
@@ -55,6 +55,8 @@ int fanotify_add_event_to_access(struct fanotify_group *group, struct fanotify_e
int fanotify_get_response_from_access(struct fanotify_group *group, struct fanotify_event *event)
{
int ret;
+
+retry:
ret = wait_event_interruptible_timeout(group->access_waitq,
event->response,
msecs_to_jiffies(5000));
@@ -89,13 +91,25 @@ int fanotify_get_response_from_access(struct fanotify_group *group, struct fanot
}

/* userspace responded, convert to something usable */
+ spin_lock(&event->response_lock);
switch (event->response) {
case FAN_ALLOW:
- return 0;
+ ret = 0;
+ break;
case FAN_DENY:
+ ret = -EPERM;
+ break;
+ case FAN_RESETTIMER:
+ event->response = 0;
+ spin_unlock(&event->response_lock);
+ goto retry;
default:
- return -EPERM;
+ ret = -EPERM;
+ break;
}
+ spin_unlock(&event->response_lock);
+
+ return ret;
}

int fanotify_process_access_response(struct fanotify_group *group, unsigned long cookie, unsigned int response)
@@ -108,7 +122,7 @@ int fanotify_process_access_response(struct fanotify_group *group, unsigned long
* userspace can send a valid responce or we will clean it up after the
* timeout
*/
- if (response & ~(FAN_ALLOW | FAN_DENY))
+ if (response & ~(FAN_ALLOW | FAN_DENY | FAN_RESETTIMER))
return -EINVAL;

mutex_lock(&group->access_mutex);
@@ -117,6 +131,11 @@ int fanotify_process_access_response(struct fanotify_group *group, unsigned long
continue;

event = holder->event;
+
+ /* FAN_RESETTIMER should be left on the list for later.... */
+ if (response == FAN_RESETTIMER)
+ break;
+
spin_lock(&event->holder_spinlock);
holder->event = NULL;
/* as soon as we do this the event.holder might be reused */
@@ -132,9 +151,13 @@ int fanotify_process_access_response(struct fanotify_group *group, unsigned long
if (!event)
return -ENOENT;

+ spin_lock(&event->response_lock);
event->response = response;
+ spin_unlock(&event->response_lock);
wake_up(&group->access_waitq);
- fanotify_put_event(event);
+
+ if (response != FAN_RESETTIMER)
+ fanotify_put_event(event);

return 0;
}
diff --git a/fs/notify/fanotify.h b/fs/notify/fanotify.h
index 6423af1..4f42a1f 100644
--- a/fs/notify/fanotify.h
+++ b/fs/notify/fanotify.h
@@ -48,6 +48,7 @@ struct fanotify_event {
atomic_t refcnt; /* how many groups still are using/need to send this event */
/* if waiting for a userspace access answer this is the cookie they will send back */
unsigned long cookie;
+ spinlock_t response_lock; /* protects response */
unsigned int response; /* userspace answer to question */
};

diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index 89bb02c..dd0d2db 100644
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -27,6 +27,7 @@
#include <linux/path.h>
#include <linux/sched.h>
#include <linux/slab.h>
+#include <linux/spinlock.h>

#include <linux/fanotify.h>
#include "fanotify.h"
@@ -169,6 +170,7 @@ struct fanotify_event *create_event(struct file *file, unsigned int mask)
event->holder.event = NULL;
INIT_LIST_HEAD(&event->holder.event_list);
atomic_set(&event->refcnt, 1);
+ spin_lock_init(&event->response_lock);

spin_lock_init(&event->holder_spinlock);

diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
index 7bc15ec..b01309e 100644
--- a/include/linux/fanotify.h
+++ b/include/linux/fanotify.h
@@ -49,6 +49,7 @@
/* answers will need to be either allow or deny */
#define FAN_ALLOW 0x00000001
#define FAN_DENY 0x00000002
+#define FAN_RESETTIMER 0x00000004

#include <linux/types.h>



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