On Mon, Apr 26, 2021 at 9:42 PM Gabriel Krisman Bertazi
<krisman@xxxxxxxxxxxxx> wrote:
>
> This adds support for the ring buffer mode in fanotify. It is enabled
> by a new flag FAN_PREALLOC_QUEUE passed to fanotify_init. If this flag
> is enabled, the group only allows marks that support the ring buffer
I don't like this limitation.
I think FAN_PREALLOC_QUEUE can work with other events, why not?
In any case if we keep ring buffer, please use a different set of
fanotify_ring_buffer_ops struct instead of spraying if/else all over the
event queue implementation.
> submission. In a following patch, FAN_ERROR will make use of this
> mechanism.
>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
> ---
> fs/notify/fanotify/fanotify.c | 77 +++++++++++++++++++---------
> fs/notify/fanotify/fanotify_user.c | 81 ++++++++++++++++++------------
> include/linux/fanotify.h | 5 +-
> include/uapi/linux/fanotify.h | 1 +
> 4 files changed, 105 insertions(+), 59 deletions(-)
>
> diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> index e3669d8a4a64..98591a8155a7 100644
> --- a/fs/notify/fanotify/fanotify.c
> +++ b/fs/notify/fanotify/fanotify.c
> @@ -612,6 +612,26 @@ static struct fanotify_event *fanotify_alloc_event(struct fsnotify_group *group,
> return event;
> }
>
> +static struct fanotify_event *fanotify_ring_get_slot(struct fsnotify_group *group,
> + u32 mask, const void *data,
> + int data_type)
> +{
> + size_t size = 0;
> +
> + pr_debug("%s: group=%p mask=%x size=%lu\n", __func__, group, mask, size);
> +
> + return FANOTIFY_E(fsnotify_ring_alloc_event_slot(group, size));
> +}
> +
> +static void fanotify_ring_write_event(struct fsnotify_group *group,
> + struct fanotify_event *event, u32 mask,
> + const void *data, __kernel_fsid_t *fsid)
> +{
> + fanotify_init_event(group, event, 0, mask);
> +
> + event->pid = get_pid(task_tgid(current));
> +}
> +
> /*
> * 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
> @@ -701,31 +721,38 @@ static int fanotify_handle_event(struct fsnotify_group *group, u32 mask,
> return 0;
> }
>
> - event = fanotify_alloc_event(group, mask, data, data_type, dir,
> - file_name, &fsid);
> - ret = -ENOMEM;
> - if (unlikely(!event)) {
> - /*
> - * We don't queue overflow events for permission events as
> - * there the access is denied and so no event is in fact lost.
> - */
> - if (!fanotify_is_perm_event(mask))
> - fsnotify_queue_overflow(group);
> - goto finish;
> - }
> -
> - fsn_event = &event->fse;
> - ret = fsnotify_add_event(group, fsn_event, fanotify_merge);
> - if (ret) {
> - /* Permission events shouldn't be merged */
> - BUG_ON(ret == 1 && mask & FANOTIFY_PERM_EVENTS);
> - /* Our event wasn't used in the end. Free it. */
> - fsnotify_destroy_event(group, fsn_event);
> -
> - ret = 0;
> - } else if (fanotify_is_perm_event(mask)) {
> - ret = fanotify_get_response(group, FANOTIFY_PERM(event),
> - iter_info);
> + if (group->flags & FSN_SUBMISSION_RING_BUFFER) {
> + event = fanotify_ring_get_slot(group, mask, data, data_type);
> + if (IS_ERR(event))
> + return PTR_ERR(event);
So no FAN_OVERFLOW with the ring buffer implementation?
This will be unexpected for fanotify users and frankly, less useful IMO.
I also don't see the technical reason to omit the overflow event.
> + fanotify_ring_write_event(group, event, mask, data, &fsid);
> + fsnotify_ring_commit_slot(group, &event->fse);
> + } else {
> + event = fanotify_alloc_event(group, mask, data, data_type, dir,
> + file_name, &fsid);
> + ret = -ENOMEM;
> + if (unlikely(!event)) {
> + /*
> + * We don't queue overflow events for permission events as
> + * there the access is denied and so no event is in fact lost.
> + */
> + if (!fanotify_is_perm_event(mask))
> + fsnotify_queue_overflow(group);
> + goto finish;
> + }
> + fsn_event = &event->fse;
> + ret = fsnotify_add_event(group, fsn_event, fanotify_merge);
> + if (ret) {
> + /* Permission events shouldn't be merged */
> + BUG_ON(ret == 1 && mask & FANOTIFY_PERM_EVENTS);
> + /* Our event wasn't used in the end. Free it. */
> + fsnotify_destroy_event(group, fsn_event);
> +
> + ret = 0;
> + } else if (fanotify_is_perm_event(mask)) {
> + ret = fanotify_get_response(group, FANOTIFY_PERM(event),
> + iter_info);
> + }
> }
> finish:
> if (fanotify_is_perm_event(mask))
> diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> index fe605359af88..5031198bf7db 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -521,7 +521,9 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
> * Permission events get queued to wait for response. Other
> * events can be destroyed now.
> */
> - if (!fanotify_is_perm_event(event->mask)) {
> + if (group->fanotify_data.flags & FAN_PREALLOC_QUEUE) {
> + fsnotify_ring_buffer_consume_event(group, &event->fse);
> + } else if (!fanotify_is_perm_event(event->mask)) {
> fsnotify_destroy_event(group, &event->fse);
> } else {
> if (ret <= 0) {
> @@ -587,40 +589,39 @@ static int fanotify_release(struct inode *ignored, struct file *file)
> */
> fsnotify_group_stop_queueing(group);
>
> - /*
> - * Process all permission events on access_list and notification queue
> - * and simulate reply from userspace.
> - */
> - spin_lock(&group->notification_lock);
> - while (!list_empty(&group->fanotify_data.access_list)) {
> - struct fanotify_perm_event *event;
> -
> - 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);
> + if (!(group->flags & FSN_SUBMISSION_RING_BUFFER)) {
> + /*
> + * Process all permission events on access_list and notification queue
> + * and simulate reply from userspace.
> + */
> spin_lock(&group->notification_lock);
> - }
> -
> - /*
> - * Destroy all non-permission events. For permission events just
> - * dequeue them and set the response. They will be freed once the
> - * response is consumed and fanotify_get_response() returns.
> - */
> - while (!fsnotify_notify_queue_is_empty(group)) {
> - struct fanotify_event *event;
> -
> - event = FANOTIFY_E(fsnotify_remove_first_event(group));
> - if (!(event->mask & FANOTIFY_PERM_EVENTS)) {
> - spin_unlock(&group->notification_lock);
> - fsnotify_destroy_event(group, &event->fse);
> - } else {
> - finish_permission_event(group, FANOTIFY_PERM(event),
> - FAN_ALLOW);
> + while (!list_empty(&group->fanotify_data.access_list)) {
> + struct fanotify_perm_event *event;
> + 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);
> + spin_lock(&group->notification_lock);
> }
> - spin_lock(&group->notification_lock);
> + /*
> + * Destroy all non-permission events. For permission events just
> + * dequeue them and set the response. They will be freed once the
> + * response is consumed and fanotify_get_response() returns.
> + */
> + while (!fsnotify_notify_queue_is_empty(group)) {
> + struct fanotify_event *event;
> + event = FANOTIFY_E(fsnotify_remove_first_event(group));
> + if (!(event->mask & FANOTIFY_PERM_EVENTS)) {
> + spin_unlock(&group->notification_lock);
> + fsnotify_destroy_event(group, &event->fse);
> + } else {
> + finish_permission_event(group, FANOTIFY_PERM(event),
> + FAN_ALLOW);
> + }
> + spin_lock(&group->notification_lock);
> + }
> + spin_unlock(&group->notification_lock);
> }
> - spin_unlock(&group->notification_lock);
>
> /* Response for all permission events it set, wakeup waiters */
> wake_up(&group->fanotify_data.access_waitq);
> @@ -981,6 +982,16 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
> if (flags & FAN_NONBLOCK)
> f_flags |= O_NONBLOCK;
>
> + if (flags & FAN_PREALLOC_QUEUE) {
> + if (!capable(CAP_SYS_ADMIN))
> + return -EPERM;
> +
> + if (flags & FAN_UNLIMITED_QUEUE)
> + return -EINVAL;
> +
> + fsn_flags = FSN_SUBMISSION_RING_BUFFER;
> + }
> +
> /* fsnotify_alloc_group takes a ref. Dropped in fanotify_release */
> group = fsnotify_alloc_user_group(&fanotify_fsnotify_ops, fsn_flags);
> if (IS_ERR(group)) {
> @@ -1223,6 +1234,10 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
> goto fput_and_out;
> }
>
> + if ((group->flags & FSN_SUBMISSION_RING_BUFFER) &&
> + (mask & ~FANOTIFY_SUBMISSION_BUFFER_EVENTS))
> + goto fput_and_out;
> +
> ret = fanotify_find_path(dfd, pathname, &path, flags,
> (mask & ALL_FSNOTIFY_EVENTS), obj_type);
> if (ret)
> @@ -1327,7 +1342,7 @@ SYSCALL32_DEFINE6(fanotify_mark,
> */
> static int __init fanotify_user_setup(void)
> {
> - BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 10);
> + BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 11);
> BUILD_BUG_ON(HWEIGHT32(FANOTIFY_MARK_FLAGS) != 9);
>
> fanotify_mark_cache = KMEM_CACHE(fsnotify_mark,
> diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
> index 3e9c56ee651f..5a4cefb4b1c3 100644
> --- a/include/linux/fanotify.h
> +++ b/include/linux/fanotify.h
> @@ -23,7 +23,8 @@
> #define FANOTIFY_INIT_FLAGS (FANOTIFY_CLASS_BITS | FANOTIFY_FID_BITS | \
> FAN_REPORT_TID | \
> FAN_CLOEXEC | FAN_NONBLOCK | \
> - FAN_UNLIMITED_QUEUE | FAN_UNLIMITED_MARKS)
> + FAN_UNLIMITED_QUEUE | FAN_UNLIMITED_MARKS | \
> + FAN_PREALLOC_QUEUE)
>
> #define FANOTIFY_MARK_TYPE_BITS (FAN_MARK_INODE | FAN_MARK_MOUNT | \
> FAN_MARK_FILESYSTEM)
> @@ -71,6 +72,8 @@
> FANOTIFY_PERM_EVENTS | \
> FAN_Q_OVERFLOW | FAN_ONDIR)
>
> +#define FANOTIFY_SUBMISSION_BUFFER_EVENTS 0
FANOTIFY_RING_BUFFER_EVENTS? FANOTIFY_PREALLOC_EVENTS?
Please leave a comment above to state what this group means.
I *think* there is no reason to limit the set of events, only the sort of
information that is possible with FAN_PREALLOC_QUEUE.
Perhaps FAN_REPORT_FID cannot be allowed and as a result
FANOTIFY_INODE_EVENTS will not be allowed, but I am not even
sure if that limitation is needed.
Thanks,
Amir.
