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.
TODO: Add some mechanism to help users discover available fastpath
handlers. For example, we can add a sysctl which is similar to
net.ipv4.tcp_available_congestion_control, or we can add some sysfs
entries.
Signed-off-by: Song Liu <song@xxxxxxxxxx>
---
fs/notify/fanotify/Makefile | 2 +-
fs/notify/fanotify/fanotify.c | 25 ++++
fs/notify/fanotify/fanotify_fastpath.c | 171 +++++++++++++++++++++++++
fs/notify/fanotify/fanotify_user.c | 7 +
include/linux/fanotify.h | 45 +++++++
include/linux/fsnotify_backend.h | 3 +
include/uapi/linux/fanotify.h | 26 ++++
7 files changed, 278 insertions(+), 1 deletion(-)
create mode 100644 fs/notify/fanotify/fanotify_fastpath.c
diff --git a/fs/notify/fanotify/Makefile b/fs/notify/fanotify/Makefile
index 25ef222915e5..fddab88dde37 100644
--- a/fs/notify/fanotify/Makefile
+++ b/fs/notify/fanotify/Makefile
@@ -1,2 +1,2 @@
# SPDX-License-Identifier: GPL-2.0-only
-obj-$(CONFIG_FANOTIFY) += fanotify.o fanotify_user.o
+obj-$(CONFIG_FANOTIFY) += fanotify.o fanotify_user.o fanotify_fastpath.o
diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 224bccaab4cc..a40ec06d0218 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;
BUILD_BUG_ON(FAN_ACCESS != FS_ACCESS);
BUILD_BUG_ON(FAN_MODIFY != FS_MODIFY);
@@ -933,6 +936,25 @@ 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);
+ 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;
+ }
+ }
+
event = fanotify_alloc_event(group, mask, data, data_type, dir,
file_name, &fsid, match_mask);
ret = -ENOMEM;
@@ -976,6 +998,9 @@ 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);
+
+ if (group->fanotify_data.fp_hook)
+ fanotify_fastpath_hook_free(group->fanotify_data.fp_hook);
}
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..0453a1ac25b1
--- /dev/null
+++ b/fs/notify/fanotify/fanotify_fastpath.c
@@ -0,0 +1,171 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/fanotify.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 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;
+}
+
+
+/*
+ * 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)
+{
+ 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);
+ 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)
+{
+ spin_lock(&fp_list_lock);
+ list_del_init(&ops->list);
+ spin_unlock(&fp_list_lock);
+}
+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;
+ int ret = 0;
+
+ ret = copy_from_user(&args, argp, sizeof(args));
+ if (ret)
+ return -EFAULT;
+
+ if (args.version != 1 || args.flags || args.init_args_len > 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 (fp_ops->fp_init) {
+ char *init_args = NULL;
+
+ if (args.init_args_len) {
+ init_args = strndup_user(u64_to_user_ptr(args.init_args),
+ args.init_args_len);
+ if (IS_ERR(init_args)) {
+ ret = PTR_ERR(init_args);
+ if (ret == -EINVAL)
+ ret = -E2BIG;
+ goto err_module_put;
+ }
+ }
+ ret = fp_ops->fp_init(fp_hook, init_args);
+ kfree(init_args);
+ if (ret)
+ goto err_module_put;
+ }
+ fp_hook->ops = fp_ops;
+ rcu_assign_pointer(group->fanotify_data.fp_hook, fp_hook);
+
+out:
+ fsnotify_group_unlock(group);
+ return ret;
+
+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);
+}
+
+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);
+}
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..cea95307a580 100644
--- a/include/linux/fanotify.h
+++ b/include/linux/fanotify.h
@@ -136,4 +136,49 @@
#undef FAN_ALL_PERM_EVENTS
#undef FAN_ALL_OUTGOING_EVENTS
+struct fsnotify_group;
+struct qstr;
+struct inode;
+struct fanotify_fastpath_hook;
+
+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;
+};
+
+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, const char *args);
+ void (*fp_free)(struct fanotify_fastpath_hook *hook);
+
+ char name[FAN_FP_NAME_MAX];
+ struct module *owner;
+ struct list_head list;
+ int flags;
+};
+
+enum fanotify_fastpath_return {
+ FAN_FP_RET_SEND_TO_USERSPACE = 0,
+ FAN_FP_RET_SKIP_EVENT = 1,
+};
+
+struct fanotify_fastpath_hook {
+ struct fanotify_fastpath_ops *ops;
+ void *data;
+};
+
+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);
+
#endif /* _LINUX_FANOTIFY_H */
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 3ecf7768e577..ef251b4e4e6f 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 +256,8 @@ struct fsnotify_group {
int f_flags; /* event_f_flags from fanotify_init() */
struct ucounts *ucounts;
mempool_t error_events_pool;
+
+ struct fanotify_fastpath_hook __rcu *fp_hook;
} fanotify_data;
#endif /* CONFIG_FANOTIFY */
};
diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
index 34f221d3a1b9..9c30baeebae0 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 +244,29 @@ 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 1024
+
+/* This is the arguments used to add fastpath handler to a group. */
+struct fanotify_fastpath_args {
+ /* user space pointer to the name of fastpath handler */
+ 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;
+ /* length of init_args */
+ __u32 init_args_len;
+} __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
