eventfs: Do not use attributes for events directory

The top "events" directory has a static inode (it's created when it is and
removed when the directory is removed). There's no need to use the events
ei->attr to determine its permissions. But it is used for saving the
permissions of the "events" directory for when it is created, as that is
needed for the default permissions for the files and directories
underneath it.

For example:

 # cd /sys/kernel/tracing
 # mkdir instances/foo
 # chown 1001 instances/foo/events

The files under instances/foo/events should still have the same owner as
instances/foo (which the instances/foo/events ei->attr will hold), but the
events directory now has owner 1001.

Link: https://lore.kernel.org/lkml/20240522165032.104981011@goodmis.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 320e49056d3ab31b2dda32a1ae35ea7e618bc57b..5d88c184f0fc15321993577eca50325d78db0b68 100644 (file)
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -210,7 +210,9 @@ static int eventfs_set_attr(struct mnt_idmap *idmap, struct dentry *dentry,
         * determined by the parent directory.
         */
        if (dentry->d_inode->i_mode & S_IFDIR) {
-               update_attr(&ei->attr, iattr);
+               /* Just use the inode permissions for the events directory */
+               if (!ei->is_events)
+                       update_attr(&ei->attr, iattr);
 
        } else {
                name = dentry->d_name.name;
@@ -789,14 +791,12 @@ struct eventfs_inode *eventfs_create_events_dir(const char *name, struct dentry
        uid = d_inode(dentry->d_parent)->i_uid;
        gid = d_inode(dentry->d_parent)->i_gid;
 
-       ei->attr.uid = uid;
-       ei->attr.gid = gid;
-
        /*
-        * When the "events" directory is created, it takes on the
-        * permissions of its parent. But can be reset on remount.
+        * The ei->attr will be used as the default values for the
+        * files beneath this directory.
         */
-       ei->attr.mode |= EVENTFS_SAVE_UID | EVENTFS_SAVE_GID;
+       ei->attr.uid = uid;
+       ei->attr.gid = gid;
 
        INIT_LIST_HEAD(&ei->children);
        INIT_LIST_HEAD(&ei->list);