linux-kernel - Re: [PATCH] eventfs: Have event files and directories default to parent uid and gid

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Message-ID: <20231220111356.54ea0ed2@gandalf.local.home>
Date: Wed, 20 Dec 2023 11:13:56 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: LKML <linux-kernel@...r.kernel.org>, Linux Trace Kernel
 <linux-trace-kernel@...r.kernel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Dongliang Cui
 <cuidongliang390@...il.com>, Hongyu Jin  <hongyu.jin@...soc.com>,
 linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] eventfs: Have event files and directories default to
 parent uid and gid

On Wed, 20 Dec 2023 10:50:17 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> 
> Dongliang reported:
> 
>   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.
> 
> To fix this, have the files created default to taking the ownership of
> the parent dentry unless the ownership was previously set by the user.
> 
> Link: https://lore.kernel.org/linux-trace-kernel/1703063706-30539-1-git-send-email-dongliang.cui@unisoc.com/
> 

I forgot to add:

  Cc: stable@...r.kernel.org
  Fixes: 28e12c09f5aa0 ("eventfs: Save ownership and mode")


-- Steve

> Reported-by: Dongliang Cui <cuidongliang390@...il.com>
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> ---
>  fs/tracefs/event_inode.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> 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;