fanotify fastpath handler enables handling fanotify events within the
kernel, and thus saves a trip to the user space. fanotify fastpath handler
can be useful in many use cases. For example, if a user is only interested
in events for some files in side a directory, a fastpath handler can be
used to filter out irrelevant events.
fanotify fastpath handler is attached to fsnotify_group. At most one
fastpath handler can be attached to a fsnotify_group. The attach/detach
of fastpath handlers are controlled by two new ioctls on the fanotify fds:
FAN_IOC_ADD_FP and FAN_IOC_DEL_FP.
fanotify fastpath handler is packaged in a kernel module. In the future,
it is also possible to package fastpath handler in a BPF program. Since
loading modules requires CAP_SYS_ADMIN, _loading_ fanotify fastpath
handler in kernel modules is limited to CAP_SYS_ADMIN. However,
non-SYS_CAP_ADMIN users can _attach_ fastpath handler loaded by sys admin
to their fanotify fds. To make fanotify fastpath handler more useful
for non-CAP_SYS_ADMIN users, a fastpath handler can take arguments at
attach time.
sysfs entry /sys/kernel/fanotify_fastpath is added to help users know
which fastpath handlers are available. At the moment, files are added for
each fastpath handler: flags, desc, and init_args.
Signed-off-by: Song Liu <song@xxxxxxxxxx>
---
fs/notify/fanotify/Kconfig | 13 ++
fs/notify/fanotify/Makefile | 1 +
fs/notify/fanotify/fanotify.c | 29 +++
fs/notify/fanotify/fanotify_fastpath.c | 282 +++++++++++++++++++++++++
fs/notify/fanotify/fanotify_user.c | 7 +
include/linux/fanotify.h | 131 ++++++++++++
include/linux/fsnotify_backend.h | 4 +
include/uapi/linux/fanotify.h | 25 +++
8 files changed, 492 insertions(+)
create mode 100644 fs/notify/fanotify/fanotify_fastpath.c
diff --git a/fs/notify/fanotify/Kconfig b/fs/notify/fanotify/Kconfig
index 0e36aaf379b7..74677d3699a3 100644
--- a/fs/notify/fanotify/Kconfig
+++ b/fs/notify/fanotify/Kconfig
@@ -24,3 +24,16 @@ config FANOTIFY_ACCESS_PERMISSIONS
hierarchical storage management systems.
If unsure, say N.
+
+config FANOTIFY_FASTPATH
+ bool "fanotify fastpath handler"
+ depends on FANOTIFY
+ default y
+ help
+ Say Y here if you want to use fanotify in kernel fastpath handler.
+ The fastpath handler can be implemented in a kernel module or a
+ BPF program. The fastpath handler can speed up fanotify in many
+ use cases. For example, when the listener is only interested in
+ a subset of events.
+
+ If unsure, say Y.
\ No newline at end of file
diff --git a/fs/notify/fanotify/Makefile b/fs/notify/fanotify/Makefile
index 25ef222915e5..543cb7aa08fc 100644
--- a/fs/notify/fanotify/Makefile
+++ b/fs/notify/fanotify/Makefile
@@ -1,2 +1,3 @@
# SPDX-License-Identifier: GPL-2.0-only
obj-$(CONFIG_FANOTIFY) += fanotify.o fanotify_user.o
+obj-$(CONFIG_FANOTIFY_FASTPATH) += fanotify_fastpath.o
diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 224bccaab4cc..b395b628a58b 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -18,6 +18,8 @@
#include "fanotify.h"
+extern struct srcu_struct fsnotify_mark_srcu;
+
static bool fanotify_path_equal(const struct path *p1, const struct path *p2)
{
return p1->mnt == p2->mnt && p1->dentry == p2->dentry;
@@ -888,6 +890,7 @@ static int fanotify_handle_event(struct fsnotify_group *group, u32 mask,
struct fsnotify_event *fsn_event;
__kernel_fsid_t fsid = {};
u32 match_mask = 0;
+ struct fanotify_fastpath_hook *fp_hook __maybe_unused;
BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
@@ -933,6 +936,27 @@ static int fanotify_handle_event(struct fsnotify_group *group, u32 mask,
if (FAN_GROUP_FLAG(group, FANOTIFY_FID_BITS))
fsid = fanotify_get_fsid(iter_info);
+#ifdef CONFIG_FANOTIFY_FASTPATH
+ fp_hook = srcu_dereference(group->fanotify_data.fp_hook, &fsnotify_mark_srcu);
+ if (fp_hook) {
+ struct fanotify_fastpath_event fp_event = {
+ .mask = mask,
+ .data = data,
+ .data_type = data_type,
+ .dir = dir,
+ .file_name = file_name,
+ .fsid = &fsid,
+ .match_mask = match_mask,
+ };
+
+ ret = fp_hook->ops->fp_handler(group, fp_hook, &fp_event);
+ if (ret == FAN_FP_RET_SKIP_EVENT) {
+ ret = 0;
+ goto finish;
+ }
+ }
+#endif
+
event = fanotify_alloc_event(group, mask, data, data_type, dir,
file_name, &fsid, match_mask);
ret = -ENOMEM;
@@ -976,6 +1000,11 @@ static void fanotify_free_group_priv(struct fsnotify_group *group)
if (mempool_initialized(&group->fanotify_data.error_events_pool))
mempool_exit(&group->fanotify_data.error_events_pool);
+
+#ifdef CONFIG_FANOTIFY_FASTPATH
+ if (group->fanotify_data.fp_hook)
+ fanotify_fastpath_hook_free(group->fanotify_data.fp_hook);
+#endif
}
static void fanotify_free_path_event(struct fanotify_event *event)
diff --git a/fs/notify/fanotify/fanotify_fastpath.c b/fs/notify/fanotify/fanotify_fastpath.c
new file mode 100644
index 000000000000..f2aefcf0ca6a
--- /dev/null
+++ b/fs/notify/fanotify/fanotify_fastpath.c
@@ -0,0 +1,282 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/fanotify.h>
+#include <linux/kobject.h>
+#include <linux/module.h>
+
+#include "fanotify.h"
+
+extern struct srcu_struct fsnotify_mark_srcu;
+
+static DEFINE_SPINLOCK(fp_list_lock);
+static LIST_HEAD(fp_list);
+
+static struct kobject *fan_fp_root_kobj;
+
+static struct {
+ enum fanotify_fastpath_flags flag;
+ const char *name;
+} fanotify_fastpath_flags_names[] = {
+ {
+ .flag = FAN_FP_F_SYS_ADMIN_ONLY,
+ .name = "SYS_ADMIN_ONLY",
+ }
+};
+
+static ssize_t flags_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ struct fanotify_fastpath_ops *ops;
+ ssize_t len = 0;
+ int i;
+
+ ops = container_of(kobj, struct fanotify_fastpath_ops, kobj);
+ for (i = 0; i < ARRAY_SIZE(fanotify_fastpath_flags_names); i++) {
+ if (ops->flags & fanotify_fastpath_flags_names[i].flag) {
+ len += sysfs_emit_at(buf, len, "%s%s", len ? " " : "",
+ fanotify_fastpath_flags_names[i].name);
+ }
+ }
+ len += sysfs_emit_at(buf, len, "\n");
+ return len;
+}
+
+static ssize_t desc_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ struct fanotify_fastpath_ops *ops;
+
+ ops = container_of(kobj, struct fanotify_fastpath_ops, kobj);
+
+ return sysfs_emit(buf, "%s\n", ops->desc ?: "N/A");
+}
+
+static ssize_t init_args_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ struct fanotify_fastpath_ops *ops;
+
+ ops = container_of(kobj, struct fanotify_fastpath_ops, kobj);
+
+ return sysfs_emit(buf, "%s\n", ops->init_args ?: "N/A");
+}
+
+static struct kobj_attribute flags_kobj_attr = __ATTR_RO(flags);
+static struct kobj_attribute desc_kobj_attr = __ATTR_RO(desc);
+static struct kobj_attribute init_args_kobj_attr = __ATTR_RO(init_args);
+
+static struct attribute *fan_fp_attrs[] = {
+ &flags_kobj_attr.attr,
+ &desc_kobj_attr.attr,
+ &init_args_kobj_attr.attr,
+ NULL,
+};
+ATTRIBUTE_GROUPS(fan_fp);
+
+static void fan_fp_kobj_release(struct kobject *kobj)
+{
+
+}
+
+static const struct kobj_type fan_fp_ktype = {
+ .release = fan_fp_kobj_release,
+ .sysfs_ops = &kobj_sysfs_ops,
+ .default_groups = fan_fp_groups,
+};
+
+static struct fanotify_fastpath_ops *fanotify_fastpath_find(const char *name)
+{
+ struct fanotify_fastpath_ops *ops;
+
+ list_for_each_entry(ops, &fp_list, list) {
+ if (!strcmp(ops->name, name))
+ return ops;
+ }
+ return NULL;
+}
+
+static void __fanotify_fastpath_unregister(struct fanotify_fastpath_ops *ops)
+{
+ spin_lock(&fp_list_lock);
+ list_del_init(&ops->list);
+ spin_unlock(&fp_list_lock);
+}
+
+/*
+ * fanotify_fastpath_register - Register a new fastpath handler.
+ *
+ * Add a fastpath handler to the fp_list. These fastpath handlers are
+ * available for all users in the system.
+ *
+ * @ops: pointer to fanotify_fastpath_ops to add.
+ *
+ * Returns:
+ * 0 - on success;
+ * -EEXIST - fastpath handler of the same name already exists.
+ */
+int fanotify_fastpath_register(struct fanotify_fastpath_ops *ops)
+{
+ int ret;
+
+ spin_lock(&fp_list_lock);
+ if (fanotify_fastpath_find(ops->name)) {
+ /* cannot register two handlers with the same name */
+ spin_unlock(&fp_list_lock);
+ return -EEXIST;
+ }
+ list_add_tail(&ops->list, &fp_list);
+ spin_unlock(&fp_list_lock);
+
+
+ kobject_init(&ops->kobj, &fan_fp_ktype);
+ ret = kobject_add(&ops->kobj, fan_fp_root_kobj, "%s", ops->name);
+ if (ret) {
+ __fanotify_fastpath_unregister(ops);
+ return ret;
+ }
+ return 0;
+}
+EXPORT_SYMBOL_GPL(fanotify_fastpath_register);
+
+/*
+ * fanotify_fastpath_unregister - Unregister a new fastpath handler.
+ *
+ * Remove a fastpath handler from fp_list.
+ *
+ * @ops: pointer to fanotify_fastpath_ops to remove.
+ */
+void fanotify_fastpath_unregister(struct fanotify_fastpath_ops *ops)
+{
+ kobject_put(&ops->kobj);
+ __fanotify_fastpath_unregister(ops);
+}
+EXPORT_SYMBOL_GPL(fanotify_fastpath_unregister);
+
+/*
+ * fanotify_fastpath_add - Add a fastpath handler to fsnotify_group.
+ *
+ * Add a fastpath handler from fp_list to a fsnotify_group.
+ *
+ * @group: fsnotify_group that will have add
+ * @argp: fanotify_fastpath_args that specifies the fastpath handler
+ * and the init arguments of the fastpath handler.
+ *
+ * Returns:
+ * 0 - on success;
+ * -EEXIST - fastpath handler of the same name already exists.
+ */
+int fanotify_fastpath_add(struct fsnotify_group *group,
+ struct fanotify_fastpath_args __user *argp)
+{
+ struct fanotify_fastpath_hook *fp_hook;
+ struct fanotify_fastpath_ops *fp_ops;
+ struct fanotify_fastpath_args args;
+ void *init_args = NULL;
+ int ret = 0;
+
+ ret = copy_from_user(&args, argp, sizeof(args));
+ if (ret)
+ return -EFAULT;
+
+ if (args.version != 1 || args.flags || args.init_args_size > FAN_FP_ARGS_MAX)
+ return -EINVAL;
+
+ args.name[FAN_FP_NAME_MAX - 1] = '\0';
+
+ fsnotify_group_lock(group);
+
+ if (rcu_access_pointer(group->fanotify_data.fp_hook)) {
+ fsnotify_group_unlock(group);
+ return -EBUSY;
+ }
+
+ fp_hook = kzalloc(sizeof(*fp_hook), GFP_KERNEL);
+ if (!fp_hook) {
+ ret = -ENOMEM;
+ goto out;
+ }
+
+ spin_lock(&fp_list_lock);
+ fp_ops = fanotify_fastpath_find(args.name);
+ if (!fp_ops || !try_module_get(fp_ops->owner)) {
+ spin_unlock(&fp_list_lock);
+ ret = -ENOENT;
+ goto err_free_hook;
+ }
+ spin_unlock(&fp_list_lock);
+
+ if (!capable(CAP_SYS_ADMIN) && (fp_ops->flags & FAN_FP_F_SYS_ADMIN_ONLY)) {
+ ret = -EPERM;
+ goto err_module_put;
+ }
+
+ if (fp_ops->fp_init) {
+ if (args.init_args_size) {
+ init_args = kzalloc(args.init_args_size, GFP_KERNEL);
+ if (!init_args) {
+ ret = -ENOMEM;
+ goto err_module_put;
+ }
+ if (copy_from_user(init_args, (void __user *)args.init_args,
+ args.init_args_size)) {
+ ret = -EFAULT;
+ goto err_free_args;
+ }
+
+ }
+ ret = fp_ops->fp_init(fp_hook, init_args);
+ if (ret)
+ goto err_free_args;
+ kfree(init_args);
+ }
+ fp_hook->ops = fp_ops;
+ rcu_assign_pointer(group->fanotify_data.fp_hook, fp_hook);
+
+out:
+ fsnotify_group_unlock(group);
+ return ret;
+
+err_free_args:
+ kfree(init_args);
+err_module_put:
+ module_put(fp_ops->owner);
+err_free_hook:
+ kfree(fp_hook);
+ goto out;
+}
+
+void fanotify_fastpath_hook_free(struct fanotify_fastpath_hook *fp_hook)
+{
+ if (fp_hook->ops->fp_free)
+ fp_hook->ops->fp_free(fp_hook);
+
+ module_put(fp_hook->ops->owner);
+ kfree(fp_hook);
+}
+
+/*
+ * fanotify_fastpath_add - Delete a fastpath handler from fsnotify_group.
+ */
+void fanotify_fastpath_del(struct fsnotify_group *group)
+{
+ struct fanotify_fastpath_hook *fp_hook;
+
+ fsnotify_group_lock(group);
+ fp_hook = group->fanotify_data.fp_hook;
+ if (!fp_hook)
+ goto out;
+
+ rcu_assign_pointer(group->fanotify_data.fp_hook, NULL);
+ fanotify_fastpath_hook_free(fp_hook);
+
+out:
+ fsnotify_group_unlock(group);
+}
+
+static int __init fanotify_fastpath_init(void)
+{
+ fan_fp_root_kobj = kobject_create_and_add("fanotify_fastpath", kernel_kobj);
+ if (!fan_fp_root_kobj)
+ return -ENOMEM;
+ return 0;
+}
+device_initcall(fanotify_fastpath_init);
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 8e2d43fc6f7c..e96cb83f8409 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -987,6 +987,13 @@ static long fanotify_ioctl(struct file *file, unsigned int cmd, unsigned long ar
spin_unlock(&group->notification_lock);
ret = put_user(send_len, (int __user *) p);
break;
+ case FAN_IOC_ADD_FP:
+ ret = fanotify_fastpath_add(group, p);
+ break;
+ case FAN_IOC_DEL_FP:
+ fanotify_fastpath_del(group);
+ ret = 0;
+ break;
}
return ret;
diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
index 89ff45bd6f01..8645d0b29e9d 100644
--- a/include/linux/fanotify.h
+++ b/include/linux/fanotify.h
@@ -2,6 +2,7 @@
#ifndef _LINUX_FANOTIFY_H
#define _LINUX_FANOTIFY_H
+#include <linux/kobject.h>
#include <linux/sysctl.h>
#include <uapi/linux/fanotify.h>
@@ -136,4 +137,134 @@
#undef FAN_ALL_PERM_EVENTS
#undef FAN_ALL_OUTGOING_EVENTS
+struct fsnotify_group;
+struct qstr;
+struct inode;
+struct fanotify_fastpath_hook;
+
+/*
+ * Event passed to fanotify fastpath handler
+ *
+ * @mask: event type and flags
+ * @data: object that event happened on
+ * @data_type: type of object for fanotify_data_XXX() accessors
+ * @dir: optional directory associated with event -
+ * if @file_name is not NULL, this is the directory that
+ * @file_name is relative to
+ * @file_name: optional file name associated with event
+ * @match_mask: mark types of this group that matched the event
+ */
+struct fanotify_fastpath_event {
+ u32 mask;
+ const void *data;
+ int data_type;
+ struct inode *dir;
+ const struct qstr *file_name;
+ __kernel_fsid_t *fsid;
+ u32 match_mask;
+};
+
+/*
+ * fanotify fastpath handler should implement these ops.
+ *
+ * fp_handler - Main call for the fastpath handler.
+ * @group: The group being notified
+ * @fp_hook: fanotify_fastpath_hook for the attach on @group.
+ * Returns: enum fanotify_fastpath_return.
+ *
+ * fp_init - Initialize the fanotify_fastpath_hook.
+ * @hook: fanotify_fastpath_hook to be initialized
+ * @args: Arguments used to initialize @hook
+ *
+ * fp_free - Free the fanotify_fastpath_hook.
+ * @hook: fanotify_fastpath_hook to be freed.
+ *
+ * @name: Name of the fanotify_fastpath_ops. This need to be unique
+ * in the system
+ * @owner: Owner module of this fanotify_fastpath_ops
+ * @list: Attach to global list of fanotify_fastpath_ops
+ * @flags: Flags for the fanotify_fastpath_ops
+ * @desc: Description of what this fastpath handler do (optional)
+ * @init_args: Description of the init_args in a string (optional)
+ */
+struct fanotify_fastpath_ops {
+ int (*fp_handler)(struct fsnotify_group *group,
+ struct fanotify_fastpath_hook *fp_hook,
+ struct fanotify_fastpath_event *fp_event);
+ int (*fp_init)(struct fanotify_fastpath_hook *hook, void *args);
+ void (*fp_free)(struct fanotify_fastpath_hook *hook);
+
+ char name[FAN_FP_NAME_MAX];
+ struct module *owner;
+ struct list_head list;
+ u32 flags;
+ const char *desc;
+ const char *init_args;
+
+ /* internal */
+ struct kobject kobj;
+};
+
+/* Flags for fanotify_fastpath_ops->flags */
+enum fanotify_fastpath_flags {
+ /* CAP_SYS_ADMIN is required to use this fastpath handler */
+ FAN_FP_F_SYS_ADMIN_ONLY = BIT(0),
+
+ FAN_FP_F_ALL = FAN_FP_F_SYS_ADMIN_ONLY,
+};
+
+/* Return value of fp_handler */
+enum fanotify_fastpath_return {
+ /* The event should be sent to user space */
+ FAN_FP_RET_SEND_TO_USERSPACE = 0,
+ /* The event should NOT be sent to user space */
+ FAN_FP_RET_SKIP_EVENT = 1,
+};
+
+/*
+ * Hook that attaches fanotify_fastpath_ops to a group.
+ * @ops: the ops
+ * @data: per group data used by the ops
+ */
+struct fanotify_fastpath_hook {
+ struct fanotify_fastpath_ops *ops;
+ void *data;
+};
+
+#ifdef CONFIG_FANOTIFY_FASTPATH
+
+int fanotify_fastpath_register(struct fanotify_fastpath_ops *ops);
+void fanotify_fastpath_unregister(struct fanotify_fastpath_ops *ops);
+int fanotify_fastpath_add(struct fsnotify_group *group,
+ struct fanotify_fastpath_args __user *args);
+void fanotify_fastpath_del(struct fsnotify_group *group);
+void fanotify_fastpath_hook_free(struct fanotify_fastpath_hook *fp_hook);
+
+#else /* CONFIG_FANOTIFY_FASTPATH */
+
+static inline int fanotify_fastpath_register(struct fanotify_fastpath_ops *ops)
+{
+ return -EOPNOTSUPP;
+}
+
+static inline void fanotify_fastpath_unregister(struct fanotify_fastpath_ops *ops)
+{
+}
+
+static inline int fanotify_fastpath_add(struct fsnotify_group *group,
+ struct fanotify_fastpath_args __user *args)
+{
+ return -ENOENT;
+}
+
+static inline void fanotify_fastpath_del(struct fsnotify_group *group)
+{
+}
+
+static inline void fanotify_fastpath_hook_free(struct fanotify_fastpath_hook *fp_hook)
+{
+}
+
+#endif /* CONFIG_FANOTIFY_FASTPATH */
+
#endif /* _LINUX_FANOTIFY_H */
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 3ecf7768e577..9b22d9b9d0bb 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -117,6 +117,7 @@ struct fsnotify_fname;
struct fsnotify_iter_info;
struct mem_cgroup;
+struct fanotify_fastpath_hook;
/*
* Each group much define these ops. The fsnotify infrastructure will call
@@ -255,6 +256,9 @@ struct fsnotify_group {
int f_flags; /* event_f_flags from fanotify_init() */
struct ucounts *ucounts;
mempool_t error_events_pool;
+#ifdef CONFIG_FANOTIFY_FASTPATH
+ struct fanotify_fastpath_hook __rcu *fp_hook;
+#endif /* CONFIG_FANOTIFY_FASTPATH */
} fanotify_data;
#endif /* CONFIG_FANOTIFY */
};
diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
index 34f221d3a1b9..654d5ab44143 100644
--- a/include/uapi/linux/fanotify.h
+++ b/include/uapi/linux/fanotify.h
@@ -3,6 +3,7 @@
#define _UAPI_LINUX_FANOTIFY_H
#include <linux/types.h>
+#include <linux/ioctl.h>
/* the following events that user-space can register for */
#define FAN_ACCESS 0x00000001 /* File was accessed */
@@ -243,4 +244,28 @@ struct fanotify_response_info_audit_rule {
(long)(meta)->event_len >= (long)FAN_EVENT_METADATA_LEN && \
(long)(meta)->event_len <= (long)(len))
+#define FAN_FP_NAME_MAX 64
+#define FAN_FP_ARGS_MAX 64
+
+/* This is the arguments used to add fastpath handler to a group. */
+struct fanotify_fastpath_args {
+ char name[FAN_FP_NAME_MAX];
+
+ __u32 version;
+ __u32 flags;
+
+ /*
+ * user space pointer to the init args of fastpath handler,
+ * up to init_args_len (<= FAN_FP_ARGS_MAX).
+ */
+ __u64 init_args;
+ /* size of init_args */
+ __u32 init_args_size;
+} __attribute__((__packed__));
+
+#define FAN_IOC_MAGIC 'F'
+
+#define FAN_IOC_ADD_FP _IOW(FAN_IOC_MAGIC, 0, struct fanotify_fastpath_args)
+#define FAN_IOC_DEL_FP _IOW(FAN_IOC_MAGIC, 1, char[FAN_FP_NAME_MAX])
+
#endif /* _UAPI_LINUX_FANOTIFY_H */
--
2.43.5
