linux-kernel - [PATCH] tracing: Do not free "head" on error path of filter_free_subsystem

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Message-ID: <20250610093348.33c5643a@gandalf.local.home>
Date: Tue, 10 Jun 2025 09:33:48 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: LKML <linux-kernel@...r.kernel.org>, Linux Trace Kernel
 <linux-trace-kernel@...r.kernel.org>
Cc: Masami Hiramatsu <mhiramat@...nel.org>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Dan Carpenter <dan.carpenter@...aro.org>
Subject: [PATCH] tracing: Do not free "head" on error path of 
 filter_free_subsystem_filters()

From: Steven Rostedt <rostedt@...dmis.org>

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@...el.com>
Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
Closes: https://lore.kernel.org/r/202506070424.lCiNreTI-lkp@intel.com/
Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
---
 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