linux-kernel - [PATCH] tracefs/eventfs: Use dput to free the toplevel events directory

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Message-ID: <20230905183332.628d7cc0@gandalf.local.home>
Date:   Tue, 5 Sep 2023 18:33:32 -0400
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>,
        Mark Rutland <mark.rutland@....com>,
        Ajay Kaher <akaher@...are.com>,
        Zheng Yejian <zhengyejian1@...wei.com>
Subject: [PATCH] tracefs/eventfs: Use dput to free the toplevel events
 directory

From: "Steven Rostedt (Google)" <rostedt@...dmis.org>

Currently when rmdir on an instance is done, eventfs_remove_events_dir()
is called and it does a dput on the dentry and then frees the
eventfs_inode that represents the events directory.

But there's no protection against a reader reading the top level events
directory at the same time and we can get a use after free error. Instead,
use the dput() associated to the dentry to also free the eventfs_inode
associated to the events directory, as that will get called when the last
reference to the directory is released.

Link: https://lore.kernel.org/all/1cb3aee2-19af-c472-e265-05176fe9bd84@huawei.com/

Fixes: 5bdcd5f5331a2 eventfs: ("Implement removal of meta data from eventfs")
Reported-by: Zheng Yejian <zhengyejian1@...wei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 fs/tracefs/event_inode.c | 15 ++++++++++++---
 fs/tracefs/inode.c       |  2 +-
 fs/tracefs/internal.h    |  5 +++--
 3 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index fa1a1679a886..f4ceae9eac19 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -185,17 +185,27 @@ static struct dentry *create_dir(const char *name, struct dentry *parent, void *
 
 /**
  * eventfs_set_ef_status_free - set the ef->status to free
+ * @ti: the tracefs_inode of the dentry
  * @dentry: dentry who's status to be freed
  *
  * eventfs_set_ef_status_free will be called if no more
  * references remain
  */
-void eventfs_set_ef_status_free(struct dentry *dentry)
+void eventfs_set_ef_status_free(struct tracefs_inode *ti, struct dentry *dentry)
 {
 	struct tracefs_inode *ti_parent;
+	struct eventfs_inode *ei;
 	struct eventfs_file *ef;
 
 	mutex_lock(&eventfs_mutex);
+
+	/* The top level events directory may be freed by this */
+	if (unlikely(ti->flags & TRACEFS_EVENT_TOP_INODE)) {
+		ei = ti->private;
+		kfree(ei);
+		goto out;
+	}
+
 	ti_parent = get_tracefs(dentry->d_parent->d_inode);
 	if (!ti_parent || !(ti_parent->flags & TRACEFS_EVENT_INODE))
 		goto out;
@@ -510,7 +520,7 @@ struct dentry *eventfs_create_events_dir(const char *name,
 	INIT_LIST_HEAD(&ei->e_top_files);
 
 	ti = get_tracefs(inode);
-	ti->flags |= TRACEFS_EVENT_INODE;
+	ti->flags |= TRACEFS_EVENT_INODE | TRACEFS_EVENT_TOP_INODE;
 	ti->private = ei;
 
 	inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
@@ -818,5 +828,4 @@ void eventfs_remove_events_dir(struct dentry *dentry)
 	ei = ti->private;
 	d_invalidate(dentry);
 	dput(dentry);
-	kfree(ei);
 }
diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index 3b8dd938b1c8..891653ba9cf3 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -385,7 +385,7 @@ static void tracefs_dentry_iput(struct dentry *dentry, struct inode *inode)
 
 	ti = get_tracefs(inode);
 	if (ti && ti->flags & TRACEFS_EVENT_INODE)
-		eventfs_set_ef_status_free(dentry);
+		eventfs_set_ef_status_free(ti, dentry);
 	iput(inode);
 }
 
diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h
index 69c2b1d87c46..4f2e49e2197b 100644
--- a/fs/tracefs/internal.h
+++ b/fs/tracefs/internal.h
@@ -3,7 +3,8 @@
 #define _TRACEFS_INTERNAL_H
 
 enum {
-	TRACEFS_EVENT_INODE     = BIT(1),
+	TRACEFS_EVENT_INODE		= BIT(1),
+	TRACEFS_EVENT_TOP_INODE		= BIT(2),
 };
 
 struct tracefs_inode {
@@ -24,6 +25,6 @@ struct inode *tracefs_get_inode(struct super_block *sb);
 struct dentry *eventfs_start_creating(const char *name, struct dentry *parent);
 struct dentry *eventfs_failed_creating(struct dentry *dentry);
 struct dentry *eventfs_end_creating(struct dentry *dentry);
-void eventfs_set_ef_status_free(struct dentry *dentry);
+void eventfs_set_ef_status_free(struct tracefs_inode *ti, struct dentry *dentry);
 
 #endif /* _TRACEFS_INTERNAL_H */
-- 
2.40.1