[PATCH v2] tracefs: Zero out the tracefs_inode when allocating it

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@xxxxxxxxxxx>

eventfs uses the tracefs_inode and assumes that it's already initialized
to zero. That is, it doesn't set fields to zero (like ti->private) after
getting its tracefs_inode. This causes bugs due to stale values.

Just initialize the entire structure to zero on allocation so there isn't
any more surprises.

This is a partial fix for accessing ti->private. The assignment still needs
to be made before the dentry is instantiated.

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 5790b1fb3d672 ("eventfs: Remove eventfs_file and just use eventfs_inode")
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-lkp/202401291043.e62e89dc-oliver.sang@xxxxxxxxx
Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
Changes since v1: https://lore.kernel.org/all/20240130151737.6e97ae00@xxxxxxxxxxxxxxxxxx/

- I didn't realize the slab had a constructor which prohibits __GFP_ZERO.
  Just use memset() in the constructor. I noticed the WARN_ON_ONCE
  that was triggering early in the boot process.

 fs/tracefs/inode.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index e1b172c0e091..636180d45c62 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -38,8 +38,6 @@ static struct inode *tracefs_alloc_inode(struct super_block *sb)
 	if (!ti)
 		return NULL;
 
-	ti->flags = 0;
-
 	return &ti->vfs_inode;
 }
 
@@ -779,6 +777,7 @@ static void init_once(void *foo)
 {
 	struct tracefs_inode *ti = (struct tracefs_inode *) foo;
 
+	memset(ti, 0, sizeof(*ti));
 	inode_init_once(&ti->vfs_inode);
 }
 
-- 
2.43.0