[for-linus][PATCH 4/9] eventfs: Free all of the eventfs_inode after RCU

Steven Rostedt
2024-05-03T22:50:34Z

The freeing of eventfs_inode via a kfree_rcu() callback. But the content
of the eventfs_inode was being freed after the last kref. This is
dangerous, as changes are being made that can access the content of an
eventfs_inode from an RCU loop.

Instead of using kfree_rcu() use call_rcu() that calls a function to do
all the freeing of the eventfs_inode after a RCU grace period has expired.

Link: https://lore.kernel.org/linux-trace-kernel/20240502200905.370261163@goodmis.org

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Fixes: 43aa6f97c2d03 ("eventfs: Get rid of dentry pointers without refcounts")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
fs/tracefs/event_inode.c | 25 ++++++++++++++++---------
1 file changed, 16 insertions(+), 9 deletions(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index f5510e26f0f6..cc8b838bbe62 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -73,6 +73,21 @@ enum {

#define EVENTFS_MODE_MASK (EVENTFS_SAVE_MODE - 1)

+static void free_ei_rcu(struct rcu_head *rcu)
+{
+ struct eventfs_inode *ei = container_of(rcu, struct eventfs_inode, rcu);
+ struct eventfs_root_inode *rei;
+
+ kfree(ei->entry_attrs);
+ kfree_const(ei->name);
+ if (ei->is_events) {
+ rei = get_root_inode(ei);
+ kfree(rei);
+ } else {
+ kfree(ei);
+ }
+}
+
/*
* eventfs_inode reference count management.
*
@@ -85,7 +100,6 @@ static void release_ei(struct kref *ref)
{
struct eventfs_inode *ei = container_of(ref, struct eventfs_inode, kref);
const struct eventfs_entry *entry;
- struct eventfs_root_inode *rei;

WARN_ON_ONCE(!ei->is_freed);

@@ -95,14 +109,7 @@ static void release_ei(struct kref *ref)
entry->release(entry->name, ei->data);
}

- kfree(ei->entry_attrs);
- kfree_const(ei->name);
- if (ei->is_events) {
- rei = get_root_inode(ei);
- kfree_rcu(rei, ei.rcu);
- } else {
- kfree_rcu(ei, rcu);
- }
+ call_rcu(&ei->rcu, free_ei_rcu);
}

static inline void put_ei(struct eventfs_inode *ei)
--
2.43.0