Commit f0ece16ffca7 for kernel

commit f0ece16ffca7384787b692431961ce202907acf5
Author: Steven Rostedt <rostedt@goodmis.org>
Date:   Sat Aug 8 09:42:15 2026 -0400

    eventfs: Use children field for rcu head and add memory barriers

    When an eventfs inode is freed, it sets ei->is_freed and then uses its
    ei->list to add it to the srcu link list as the list field is a union with
    the rcu list head. As the ei->list is used to iterate over an SRCU
    protected list without taking the eventfs_mutex, there's nothing stopping
    the iteration over that list to see the ei->rcu instead of the ei->list
    and it will read a corrupt target.

    To fix this, change the union of the rcu list head with the children list.
    On freeing the eventfs inode, set the is_free and execute a smp_wmb()
    before adding the eventfs inode to the SRCU list.

    On iteration of the ei->children list, at the start, execute a smp_rmb()
    and then read the is_freed of the ei to see if the children list is still
    valid. If is_freed is set, then the ei_child read is not valid and the
    loop should exit immediately.

    Cc: stable@vger.kernel.org
    Link: https://patch.msgid.link/20260808094215.4252430d@robin
    Fixes: 704f960dbee2f ("eventfs: Read ei->entries before ei->children in eventfs_iterate()")
    Reported-by: Sashiko <sashiko-bot@kernel.org>
    Closes: https://sashiko.dev/#/patchset/20260806022719.375354-1-shuangpeng.kernel%40gmail.com
    Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
    Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 93bc4f83b73e..a52458435327 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -124,7 +124,17 @@ static inline void put_ei(struct eventfs_inode *ei)
 static inline void free_ei(struct eventfs_inode *ei)
 {
 	if (ei) {
+		/* The ei should have no children if it is being freed. */
+		WARN_ON_ONCE(!list_empty(&ei->children));
 		ei->is_freed = 1;
+		/*
+		 * The SRCU iteration has a smp_rmb() to make sure it
+		 * sees a child (that may have already been freed)
+		 * before it reads is_free. If is_free is set, it must
+		 * not use the child it acquired from ei->children, as
+		 * the list may be used for SRCU.
+		 */
+		smp_wmb();
 		put_ei(ei);
 	}
 }
@@ -627,6 +637,20 @@ static int eventfs_iterate(struct file *file, struct dir_context *ctx)
 	list_for_each_entry_srcu(ei_child, &ei->children, list,
 				 srcu_read_lock_held(&eventfs_srcu)) {

+		/*
+		 * If the ei is being freed, then the ei->children may be
+		 * being used as the rcu list, which means the next element
+		 * may be garbage. The ei->is_free is set before switching
+		 * the ei->children over to ei->rcu. The read memory barrier
+		 * here makes sure the ei_child is read before is_free is
+		 * updated.
+		 *
+		 * Matches the smp_wmb() in free_ei()
+		 */
+		smp_rmb();
+		if (ei->is_freed)
+			return -EINVAL;
+
 		if (c > 0) {
 			c--;
 			continue;
diff --git a/fs/tracefs/internal.h b/fs/tracefs/internal.h
index a4a7f8431aff..c61481d04c8e 100644
--- a/fs/tracefs/internal.h
+++ b/fs/tracefs/internal.h
@@ -46,11 +46,11 @@ struct eventfs_attr {
  * @ino:	The saved inode number
  */
 struct eventfs_inode {
+	struct list_head	list;
 	union {
-		struct list_head	list;
+		struct list_head	children;
 		struct rcu_head		rcu;
 	};
-	struct list_head		children;
 	const struct eventfs_entry	*entries;
 	const char			*name;
 	struct eventfs_attr		*entry_attrs;