FAILED: patch "[PATCH] eventfs: Have "events" directory get permissions from its" failed to apply to 6.8-stable tree

The patch below does not apply to the 6.8-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.8.y
git checkout FETCH_HEAD
git cherry-pick -x d57cf30c4c07837799edec949102b0adf58bae79
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2024051331-sediment-viewable-33bc@gregkh' --subject-prefix 'PATCH 6.8.y' HEAD^..

Possible dependencies:

d57cf30c4c07 ("eventfs: Have "events" directory get permissions from its parent") d53891d348ac ("eventfs: Do not differentiate the toplevel events directory") c3137ab6318d ("eventfs: Create eventfs_root_inode to store dentry")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d57cf30c4c07837799edec949102b0adf58bae79 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Google)" <[email protected]>
Date: Thu, 2 May 2024 16:08:27 -0400
Subject: [PATCH] eventfs: Have "events" directory get permissions from its
parent

The events directory gets its permissions from the root inode. But this can cause an inconsistency if the instances directory changes its permissions, as the permissions of the created directories under it should inherit the permissions of the instances directory when directories under it are created.

Currently the behavior is:

 # cd /sys/kernel/tracing
 # chgrp 1002 instances
 # mkdir instances/foo
 # ls -l instances/foo
[..]
 -r--r-----  1 root lkp  0 May  1 18:55 buffer_total_size_kb
 -rw-r-----  1 root lkp  0 May  1 18:55 current_tracer
 -rw-r-----  1 root lkp  0 May  1 18:55 error_log
 drwxr-xr-x  1 root root 0 May  1 18:55 events
 --w-------  1 root lkp  0 May  1 18:55 free_buffer
 drwxr-x---  2 root lkp  0 May  1 18:55 options
 drwxr-x--- 10 root lkp  0 May  1 18:55 per_cpu
 -rw-r-----  1 root lkp  0 May  1 18:55 set_event

All the files and directories under "foo" has the "lkp" group except the "events" directory. That's because its getting its default value from the mount point instead of its parent.

Have the "events" directory make its default value based on its parent's permissions. That now gives:

 # ls -l instances/foo
[..]
 -rw-r-----  1 root lkp 0 May  1 21:16 buffer_subbuf_size_kb
 -r--r-----  1 root lkp 0 May  1 21:16 buffer_total_size_kb
 -rw-r-----  1 root lkp 0 May  1 21:16 current_tracer
 -rw-r-----  1 root lkp 0 May  1 21:16 error_log
 drwxr-xr-x  1 root lkp 0 May  1 21:16 events
 --w-------  1 root lkp 0 May  1 21:16 free_buffer
 drwxr-x---  2 root lkp 0 May  1 21:16 options
 drwxr-x--- 10 root lkp 0 May  1 21:16 per_cpu
 -rw-r-----  1 root lkp 0 May  1 21:16 set_event

index 6e08405892ae..a878cea70f4c 100644
@@ -37,6 +37,7 @@ static DEFINE_MUTEX(eventfs_mutex);
 
 struct eventfs_root_inode {
 	struct eventfs_inode		ei;
+	struct inode			*parent_inode;
 	struct dentry			*events_dir;
 };
 

@@ -226,12 +227,23 @@ static int eventfs_set_attr(struct mnt_idmap *idmap, struct dentry *dentry,
 
 static void update_events_attr(struct eventfs_inode *ei, struct super_block *sb)
 {
-	struct inode *root;
+	struct eventfs_root_inode *rei;
+	struct inode *parent;
 
-	/* Get the tracefs root inode. */
-	root = d_inode(sb->s_root);
-	ei->attr.uid = root->i_uid;
-	ei->attr.gid = root->i_gid;
+	rei = get_root_inode(ei);
+
+	/* Use the parent inode permissions unless root set its permissions */
+	parent = rei->parent_inode;
+
+	if (rei->ei.attr.mode & EVENTFS_SAVE_UID)
+		ei->attr.uid = rei->ei.attr.uid;
+	else
+		ei->attr.uid = parent->i_uid;
+
+	if (rei->ei.attr.mode & EVENTFS_SAVE_GID)
+		ei->attr.gid = rei->ei.attr.gid;
+	else
+		ei->attr.gid = parent->i_gid;
 }
 
 static void set_top_events_ownership(struct inode *inode)

@@ -817,6 +829,7 @@ struct eventfs_inode *eventfs_create_events_dir(const char *name, struct dentry
 	// Note: we have a ref to the dentry from tracefs_start_creating()
 	rei = get_root_inode(ei);
 	rei->events_dir = dentry;
+	rei->parent_inode = d_inode(dentry->d_sb->s_root);
 
 	ei->entries = entries;
 	ei->nr_entries = size;

@@ -826,10 +839,15 @@ 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;
 
-	/* This is used as the default ownership of the files and directories */
 	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.
+	 */
+	ei->attr.mode |= EVENTFS_SAVE_UID | EVENTFS_SAVE_GID;
+
 	INIT_LIST_HEAD(&ei->children);
 	INIT_LIST_HEAD(&ei->list);