[PATCH] tracing: Do not free "head" on error path of filter_free_subsystem_filters()

[Steven Rostedt]

From: Steven Rostedt <rostedt@xxxxxxxxxxx>

The variable "head" is allocated and initialized as a list before
allocating the first "item" for the list. If the allocation of "item"
fails, it frees "head" and then jumps to the label "free_now" which will
process head and free it.

This will cause a UAF of "head", and it doesn't need to free it before
jumping to the "free_now" label as that code will free it.

Fixes: a9d0aab5eb33 ("tracing: Fix regression of filter waiting a long time on RCU synchronization")
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Closes: https://lore.kernel.org/r/202506070424.lCiNreTI-lkp@xxxxxxxxx/
Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
---
 kernel/trace/trace_events_filter.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index ea8b364b6818..08141f105c95 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -1437,10 +1437,8 @@ static void filter_free_subsystem_filters(struct trace_subsystem_dir *dir,
 	INIT_LIST_HEAD(&head->list);
 
 	item = kmalloc(sizeof(*item), GFP_KERNEL);
-	if (!item) {
-		kfree(head);
+	if (!item)
 		goto free_now;
-	}
 
 	item->filter = filter;
 	list_add_tail(&item->list, &head->list);
-- 
2.47.2