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

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Date: Wed, 20 Dec 2023 17:15:06 +0800
From: Dongliang Cui <dongliang.cui@...soc.com>
To: Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu
	<mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        <linux-kernel@...r.kernel.org>, <linux-trace-kernel@...r.kernel.org>
CC: Dongliang Cui <cuidongliang390@...il.com>,
        Hongyu Jin
	<hongyu.jin@...soc.com>
Subject: [PATCH]eventfs: Apply the gid in the mounting parameters to all files

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>
---
 fs/tracefs/inode.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index ae648de..5296ff7 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -560,6 +560,16 @@ struct dentry *eventfs_failed_creating(struct dentry *dentry)
  */
 struct dentry *eventfs_end_creating(struct dentry *dentry)
 {
+	struct tracefs_fs_info *fsi;
+	struct tracefs_mount_opts *opts;
+
+	if (dentry && dentry->d_inode) {
+		fsi = dentry->d_inode->i_sb->s_fs_info;
+		opts = &fsi->mount_opts;
+		if (opts->opts & BIT(Opt_gid))
+			change_gid(dentry, opts->gid);
+	}
+
 	return dentry;
 }
 
-- 
2.7.4