fanotify: prepare for implicit event flags in mark mask

So far, all flags that can be set in an fanotify mark mask can be set
explicitly by a call to fanotify_mark(2).

Prepare for defining implicit event flags that cannot be set by user with
fanotify_mark(2), similar to how inotify/dnotify implicitly set the
FS_EVENT_ON_CHILD flag.

Implicit event flags cannot be removed by user and mark gets destroyed
when only implicit event flags remain in the mask.

Link: https://lore.kernel.org/r/20200716084230.30611-7-amir73il@gmail.com
Signed-off-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 6d30beb320f36107435bfaa7a2ee7875b8be9506..ab974cd234f7a01dddc5b96c86e97ef8880fabea 100644 (file)
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -656,12 +656,13 @@ out:
 }
 
 static __u32 fanotify_mark_remove_from_mask(struct fsnotify_mark *fsn_mark,
-                                           __u32 mask,
-                                           unsigned int flags,
-                                           int *destroy)
+                                           __u32 mask, unsigned int flags,
+                                           __u32 umask, int *destroy)
 {
        __u32 oldmask = 0;
 
+       /* umask bits cannot be removed by user */
+       mask &= ~umask;
        spin_lock(&fsn_mark->lock);
        if (!(flags & FAN_MARK_IGNORED_MASK)) {
                oldmask = fsn_mark->mask;
@@ -669,7 +670,13 @@ static __u32 fanotify_mark_remove_from_mask(struct fsnotify_mark *fsn_mark,
        } else {
                fsn_mark->ignored_mask &= ~mask;
        }
-       *destroy = !(fsn_mark->mask | fsn_mark->ignored_mask);
+       /*
+        * We need to keep the mark around even if remaining mask cannot
+        * result in any events (e.g. mask == FAN_ONDIR) to support incremenal
+        * changes to the mask.
+        * Destroy mark when only umask bits remain.
+        */
+       *destroy = !((fsn_mark->mask | fsn_mark->ignored_mask) & ~umask);
        spin_unlock(&fsn_mark->lock);
 
        return mask & oldmask;
@@ -677,7 +684,7 @@ static __u32 fanotify_mark_remove_from_mask(struct fsnotify_mark *fsn_mark,
 
 static int fanotify_remove_mark(struct fsnotify_group *group,
                                fsnotify_connp_t *connp, __u32 mask,
-                               unsigned int flags)
+                               unsigned int flags, __u32 umask)
 {
        struct fsnotify_mark *fsn_mark = NULL;
        __u32 removed;
@@ -691,7 +698,7 @@ static int fanotify_remove_mark(struct fsnotify_group *group,
        }
 
        removed = fanotify_mark_remove_from_mask(fsn_mark, mask, flags,
-                                                &destroy_mark);
+                                                umask, &destroy_mark);
        if (removed & fsnotify_conn_mask(fsn_mark->connector))
                fsnotify_recalc_mask(fsn_mark->connector);
        if (destroy_mark)
@@ -707,25 +714,26 @@ static int fanotify_remove_mark(struct fsnotify_group *group,
 
 static int fanotify_remove_vfsmount_mark(struct fsnotify_group *group,
                                         struct vfsmount *mnt, __u32 mask,
-                                        unsigned int flags)
+                                        unsigned int flags, __u32 umask)
 {
        return fanotify_remove_mark(group, &real_mount(mnt)->mnt_fsnotify_marks,
-                                   mask, flags);
+                                   mask, flags, umask);
 }
 
 static int fanotify_remove_sb_mark(struct fsnotify_group *group,
-                                     struct super_block *sb, __u32 mask,
-                                     unsigned int flags)
+                                  struct super_block *sb, __u32 mask,
+                                  unsigned int flags, __u32 umask)
 {
-       return fanotify_remove_mark(group, &sb->s_fsnotify_marks, mask, flags);
+       return fanotify_remove_mark(group, &sb->s_fsnotify_marks, mask,
+                                   flags, umask);
 }
 
 static int fanotify_remove_inode_mark(struct fsnotify_group *group,
                                      struct inode *inode, __u32 mask,
-                                     unsigned int flags)
+                                     unsigned int flags, __u32 umask)
 {
        return fanotify_remove_mark(group, &inode->i_fsnotify_marks, mask,
-                                   flags);
+                                   flags, umask);
 }
 
 static __u32 fanotify_mark_add_to_mask(struct fsnotify_mark *fsn_mark,
@@ -1175,13 +1183,13 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask,
        case FAN_MARK_REMOVE:
                if (mark_type == FAN_MARK_MOUNT)
                        ret = fanotify_remove_vfsmount_mark(group, mnt, mask,
-                                                           flags);
+                                                           flags, 0);
                else if (mark_type == FAN_MARK_FILESYSTEM)
                        ret = fanotify_remove_sb_mark(group, mnt->mnt_sb, mask,
-                                                     flags);
+                                                     flags, 0);
                else
                        ret = fanotify_remove_inode_mark(group, inode, mask,
-                                                        flags);
+                                                        flags, 0);
                break;
        default:
                ret = -EINVAL;