linux-kernel - Re: [PATCH]eventfs: Apply the gid in the mounting parameters to all files

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Date: Wed, 20 Dec 2023 08:30:58 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Dongliang Cui <dongliang.cui@...soc.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, <linux-kernel@...r.kernel.org>,
 <linux-trace-kernel@...r.kernel.org>, Dongliang Cui
 <cuidongliang390@...il.com>, Hongyu Jin <hongyu.jin@...soc.com>
Subject: Re: [PATCH]eventfs: Apply the gid in the mounting parameters to all
 files

On Wed, 20 Dec 2023 17:15:06 +0800
Dongliang Cui <dongliang.cui@...soc.com> wrote:

> I found that in the latest version, the nodes of 
> tracefs have been changed to dynamically created.
> 
> This has caused me to encounter a problem where 
> the gid I specified in the mounting parameters 
> cannot apply to all files, as in the following
> situation:
> 
> /data/tmp/events # mount | grep tracefs
> tracefs on /data/tmp type tracefs (rw,seclabel,relatime,gid=3012)
> 
> gid 3012 = readtracefs
> 
> /data/tmp # ls -lh
> total 0
> -r--r-----   1 root readtracefs 0 1970-01-01 08:00 README
> -r--r-----   1 root readtracefs 0 1970-01-01 08:00 available_events
> 
> ums9621_1h10:/data/tmp/events # ls -lh
> total 0
> drwxr-xr-x 2 root root 0 2023-12-19 00:56 alarmtimer
> drwxr-xr-x 2 root root 0 2023-12-19 00:56 asoc
> 
> It will prevent certain applications from accessing
> tracefs properly, I try to avoid this issue by making 
> the following modifications.
> 
> Signed-off-by: Dongliang Cui <dongliang.cui@...soc.com>


Thanks for the report, can you try this fix instead?

-- Steve

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 43e237864a42..2ccc849a5bda 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -148,7 +148,8 @@ static const struct file_operations eventfs_file_operations = {
 	.release	= eventfs_release,
 };
 
-static void update_inode_attr(struct inode *inode, struct eventfs_attr *attr, umode_t mode)
+static void update_inode_attr(struct dentry *dentry, struct inode *inode,
+			      struct eventfs_attr *attr, umode_t mode)
 {
 	if (!attr) {
 		inode->i_mode = mode;
@@ -162,9 +163,13 @@ static void update_inode_attr(struct inode *inode, struct eventfs_attr *attr, um
 
 	if (attr->mode & EVENTFS_SAVE_UID)
 		inode->i_uid = attr->uid;
+	else
+		inode->i_uid = d_inode(dentry->d_parent)->i_uid;
 
 	if (attr->mode & EVENTFS_SAVE_GID)
 		inode->i_gid = attr->gid;
+	else
+		inode->i_gid = d_inode(dentry->d_parent)->i_gid;
 }
 
 /**
@@ -206,7 +211,7 @@ static struct dentry *create_file(const char *name, umode_t mode,
 		return eventfs_failed_creating(dentry);
 
 	/* If the user updated the directory's attributes, use them */
-	update_inode_attr(inode, attr, mode);
+	update_inode_attr(dentry, inode, attr, mode);
 
 	inode->i_op = &eventfs_file_inode_operations;
 	inode->i_fop = fop;
@@ -242,7 +247,8 @@ static struct dentry *create_dir(struct eventfs_inode *ei, struct dentry *parent
 		return eventfs_failed_creating(dentry);
 
 	/* If the user updated the directory's attributes, use them */
-	update_inode_attr(inode, &ei->attr, S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO);
+	update_inode_attr(dentry, inode, &ei->attr,
+			  S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO);
 
 	inode->i_op = &eventfs_root_dir_inode_operations;
 	inode->i_fop = &eventfs_file_operations;