From 2cd88c498ecff8e22bf4c397b8eb226db70ac343 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Fri, 9 Oct 2026 23:51:54 +0200 Subject: [PATCH] eventfs: Free the eventfs_inode after an rcu grace period too tracefs_d_revalidate() reads ->is_freed of the eventfs_inode that dentry->d_fsdata points to, and ->d_revalidate() is called in rcu pathwalk mode with nothing but rcu_read_lock() held. The dentry itself stays around for such a walker, but tracefs_d_release() drops its reference to the eventfs_inode when the dentry is killed, and release_ei() then frees it after a grace period of eventfs_srcu. An SRCU grace period doesn't wait for rcu_read_lock() sections, so the walker can read an eventfs_inode that is already gone. With a pathwalk held up in tracefs_d_revalidate() while the dentry goes away: BUG: KASAN: slab-use-after-free in tracefs_d_revalidate+0x76/0x90 Read of size 1 at addr ff1100010152d8d0 by task walker/97 Call Trace: tracefs_d_revalidate+0x76/0x90 lookup_fast+0x320/0x640 path_lookupat+0x160/0xb00 filename_lookup+0x1f1/0x5b0 vfs_statx+0xd7/0x3b0 vfs_fstatat+0x4d/0x90 __do_sys_newfstatat+0xa0/0x100 do_syscall_64+0x10e/0x5e0 entry_SYSCALL_64_after_hwframe+0x77/0x7f [...] Allocated by task 1: __kmalloc_cache_noprof+0x249/0x560 eventfs_create_dir+0x7a/0x590 event_create_dir+0x2fb/0xcf0 trace_add_event_call+0xbf/0x150 [...] Freed by task 11: kfree+0x1db/0x5b0 srcu_invoke_callbacks+0x3a3/0x620 process_one_work+0x937/0x1810 worker_thread+0x4f1/0xd60 Before commit 8e556432477e ("eventfs: Use SRCU for freeing eventfs_inodes") release_ei() used call_rcu(), which covered the walker, while eventfs_iterate() needs the SRCU grace period. Wait for both and chain call_rcu() from the SRCU callback. Cc: stable@vger.kernel.org Fixes: 8e556432477e ("eventfs: Use SRCU for freeing eventfs_inodes") Link: https://patch.msgid.link/20261009-work-fixes-rcu-v1-4-7446d2d335e6@kernel.org Signed-off-by: Christian Brauner (Amutable) Signed-off-by: Steven Rostedt --- fs/tracefs/event_inode.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c index 6e3513b13cfa..090aca946717 100644 --- a/fs/tracefs/event_inode.c +++ b/fs/tracefs/event_inode.c @@ -91,6 +91,14 @@ static void free_ei_rcu(struct rcu_head *rcu) } } +/* read under eventfs_srcu and, by tracefs_d_revalidate(), in rcu pathwalk */ +static void free_ei_srcu(struct rcu_head *rcu) +{ + struct eventfs_inode *ei = container_of(rcu, struct eventfs_inode, rcu); + + call_rcu(&ei->rcu, free_ei_rcu); +} + /* * eventfs_inode reference count management. * @@ -112,7 +120,7 @@ static void release_ei(struct kref *ref) entry->release(entry->name, ei->data); } - call_srcu(&eventfs_srcu, &ei->rcu, free_ei_rcu); + call_srcu(&eventfs_srcu, &ei->rcu, free_ei_srcu); } static inline void put_ei(struct eventfs_inode *ei)