fanotify: introduce a generic info record copying helper

The copy_info_records_to_user() helper allows for the separation of
info record copying routines/conditionals from copy_event_to_user(),
which reduces the overall clutter within this function. This becomes
especially true as we start introducing additional info records in the
future i.e. struct fanotify_event_info_pidfd. On success, this helper
returns the total amount of bytes that have been copied into the user
supplied buffer and on error, a negative value is returned to the
caller.

The newly defined macro FANOTIFY_INFO_MODES can be used to obtain info
record types that have been enabled for a specific notification
group. This macro becomes useful in the subsequent patch when the
FAN_REPORT_PIDFD initialization flag is introduced.

Link: https://lore.kernel.org/r/8872947dfe12ce8ae6e9a7f2d49ea29bc8006af0.1628398044.git.repnop@google.com
Signed-off-by: Matthew Bobrowski <repnop@google.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 182fea2..99d145e 100644 (file)
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -173,7 +173,7 @@ static struct fanotify_event *get_one_event(struct fsnotify_group *group,
        size_t event_size = FAN_EVENT_METADATA_LEN;
        struct fanotify_event *event = NULL;
        struct fsnotify_event *fsn_event;
-       unsigned int fid_mode = FAN_GROUP_FLAG(group, FANOTIFY_FID_BITS);
+       unsigned int info_mode = FAN_GROUP_FLAG(group, FANOTIFY_INFO_MODES);
 
        pr_debug("%s: group=%p count=%zd\n", __func__, group, count);
 
@@ -183,8 +183,8 @@ static struct fanotify_event *get_one_event(struct fsnotify_group *group,
                goto out;
 
        event = FANOTIFY_E(fsn_event);
-       if (fid_mode)
-               event_size += fanotify_event_info_len(fid_mode, event);
+       if (info_mode)
+               event_size += fanotify_event_info_len(info_mode, event);
 
        if (event_size > count) {
                event = ERR_PTR(-EINVAL);
@@ -401,6 +401,86 @@ static int copy_fid_info_to_user(__kernel_fsid_t *fsid, struct fanotify_fh *fh,
        return info_len;
 }
 
+static int copy_info_records_to_user(struct fanotify_event *event,
+                                    struct fanotify_info *info,
+                                    unsigned int info_mode,
+                                    char __user *buf, size_t count)
+{
+       int ret, total_bytes = 0, info_type = 0;
+       unsigned int fid_mode = info_mode & FANOTIFY_FID_BITS;
+
+       /*
+        * Event info records order is as follows: dir fid + name, child fid.
+        */
+       if (fanotify_event_dir_fh_len(event)) {
+               info_type = info->name_len ? FAN_EVENT_INFO_TYPE_DFID_NAME :
+                                            FAN_EVENT_INFO_TYPE_DFID;
+               ret = copy_fid_info_to_user(fanotify_event_fsid(event),
+                                           fanotify_info_dir_fh(info),
+                                           info_type,
+                                           fanotify_info_name(info),
+                                           info->name_len, buf, count);
+               if (ret < 0)
+                       return ret;
+
+               buf += ret;
+               count -= ret;
+               total_bytes += ret;
+       }
+
+       if (fanotify_event_object_fh_len(event)) {
+               const char *dot = NULL;
+               int dot_len = 0;
+
+               if (fid_mode == FAN_REPORT_FID || info_type) {
+                       /*
+                        * With only group flag FAN_REPORT_FID only type FID is
+                        * reported. Second info record type is always FID.
+                        */
+                       info_type = FAN_EVENT_INFO_TYPE_FID;
+               } else if ((fid_mode & FAN_REPORT_NAME) &&
+                          (event->mask & FAN_ONDIR)) {
+                       /*
+                        * With group flag FAN_REPORT_NAME, if name was not
+                        * recorded in an event on a directory, report the name
+                        * "." with info type DFID_NAME.
+                        */
+                       info_type = FAN_EVENT_INFO_TYPE_DFID_NAME;
+                       dot = ".";
+                       dot_len = 1;
+               } else if ((event->mask & ALL_FSNOTIFY_DIRENT_EVENTS) ||
+                          (event->mask & FAN_ONDIR)) {
+                       /*
+                        * With group flag FAN_REPORT_DIR_FID, a single info
+                        * record has type DFID for directory entry modification
+                        * event and for event on a directory.
+                        */
+                       info_type = FAN_EVENT_INFO_TYPE_DFID;
+               } else {
+                       /*
+                        * With group flags FAN_REPORT_DIR_FID|FAN_REPORT_FID,
+                        * a single info record has type FID for event on a
+                        * non-directory, when there is no directory to report.
+                        * For example, on FAN_DELETE_SELF event.
+                        */
+                       info_type = FAN_EVENT_INFO_TYPE_FID;
+               }
+
+               ret = copy_fid_info_to_user(fanotify_event_fsid(event),
+                                           fanotify_event_object_fh(event),
+                                           info_type, dot, dot_len,
+                                           buf, count);
+               if (ret < 0)
+                       return ret;
+
+               buf += ret;
+               count -= ret;
+               total_bytes += ret;
+       }
+
+       return total_bytes;
+}
+
 static ssize_t copy_event_to_user(struct fsnotify_group *group,
                                  struct fanotify_event *event,
                                  char __user *buf, size_t count)
@@ -408,15 +488,14 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
        struct fanotify_event_metadata metadata;
        struct path *path = fanotify_event_path(event);
        struct fanotify_info *info = fanotify_event_info(event);
-       unsigned int fid_mode = FAN_GROUP_FLAG(group, FANOTIFY_FID_BITS);
+       unsigned int info_mode = FAN_GROUP_FLAG(group, FANOTIFY_INFO_MODES);
        struct file *f = NULL;
        int ret, fd = FAN_NOFD;
-       int info_type = 0;
 
        pr_debug("%s: group=%p event=%p\n", __func__, group, event);
 
        metadata.event_len = FAN_EVENT_METADATA_LEN +
-                               fanotify_event_info_len(fid_mode, event);
+                               fanotify_event_info_len(info_mode, event);
        metadata.metadata_len = FAN_EVENT_METADATA_LEN;
        metadata.vers = FANOTIFY_METADATA_VERSION;
        metadata.reserved = 0;
@@ -465,69 +544,11 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
        if (f)
                fd_install(fd, f);
 
-       /* Event info records order is: dir fid + name, child fid */
-       if (fanotify_event_dir_fh_len(event)) {
-               info_type = info->name_len ? FAN_EVENT_INFO_TYPE_DFID_NAME :
-                                            FAN_EVENT_INFO_TYPE_DFID;
-               ret = copy_fid_info_to_user(fanotify_event_fsid(event),
-                                           fanotify_info_dir_fh(info),
-                                           info_type,
-                                           fanotify_info_name(info),
-                                           info->name_len, buf, count);
-               if (ret < 0)
-                       goto out_close_fd;
-
-               buf += ret;
-               count -= ret;
-       }
-
-       if (fanotify_event_object_fh_len(event)) {
-               const char *dot = NULL;
-               int dot_len = 0;
-
-               if (fid_mode == FAN_REPORT_FID || info_type) {
-                       /*
-                        * With only group flag FAN_REPORT_FID only type FID is
-                        * reported. Second info record type is always FID.
-                        */
-                       info_type = FAN_EVENT_INFO_TYPE_FID;
-               } else if ((fid_mode & FAN_REPORT_NAME) &&
-                          (event->mask & FAN_ONDIR)) {
-                       /*
-                        * With group flag FAN_REPORT_NAME, if name was not
-                        * recorded in an event on a directory, report the
-                        * name "." with info type DFID_NAME.
-                        */
-                       info_type = FAN_EVENT_INFO_TYPE_DFID_NAME;
-                       dot = ".";
-                       dot_len = 1;
-               } else if ((event->mask & ALL_FSNOTIFY_DIRENT_EVENTS) ||
-                          (event->mask & FAN_ONDIR)) {
-                       /*
-                        * With group flag FAN_REPORT_DIR_FID, a single info
-                        * record has type DFID for directory entry modification
-                        * event and for event on a directory.
-                        */
-                       info_type = FAN_EVENT_INFO_TYPE_DFID;
-               } else {
-                       /*
-                        * With group flags FAN_REPORT_DIR_FID|FAN_REPORT_FID,
-                        * a single info record has type FID for event on a
-                        * non-directory, when there is no directory to report.
-                        * For example, on FAN_DELETE_SELF event.
-                        */
-                       info_type = FAN_EVENT_INFO_TYPE_FID;
-               }
-
-               ret = copy_fid_info_to_user(fanotify_event_fsid(event),
-                                           fanotify_event_object_fh(event),
-                                           info_type, dot, dot_len,
-                                           buf, count);
+       if (info_mode) {
+               ret = copy_info_records_to_user(event, info, info_mode,
+                                               buf, count);
                if (ret < 0)
                        goto out_close_fd;
-
-               buf += ret;
-               count -= ret;
        }
 
        return metadata.event_len;

diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h
index a16dbec..10a7e26 100644 (file)
--- a/include/linux/fanotify.h
+++ b/include/linux/fanotify.h
@@ -27,6 +27,8 @@ extern struct ctl_table fanotify_table[]; /* for sysctl */
 
 #define FANOTIFY_FID_BITS      (FAN_REPORT_FID | FAN_REPORT_DFID_NAME)
 
+#define FANOTIFY_INFO_MODES    (FANOTIFY_FID_BITS)
+
 /*
  * fanotify_init() flags that require CAP_SYS_ADMIN.
  * We do not allow unprivileged groups to request permission events.