Hi Steven,
On 2025/3/13 22:44, Steven Rostedt wrote:
> On Thu, 13 Mar 2025 10:37:19 +0000
> Tengda Wu <[email protected]> wrote:
>
>> The function event_{hist,hist_debug}_open() maintains the refcount of
>> 'file->tr' and 'file' through tracing_open_file_tr(), but it does not
>> roll back these counts when the subsequent single_open() call fails,
>> leading to a refcount leak.
>>
>> A very obvious case is that if the hist/hist_debug file belongs to a
>> certain instance, the failure of single_open() will prevent the deletion
>> of that instance, as it relies on the condition 'tr->ref == 1' within
>> __remove_instance().
>>
>> Fix this by calling tracing_release_file_tr() to correct the refcount
>> when single_open() fails.
>>
>> Fixes: 1cc111b9cddc ("tracing: Fix uaf issue when open the hist or
>> hist_debug file")
>> Signed-off-by: Tengda Wu <[email protected]>
>> Cc: [email protected] # v6.7+
>> ---
>> kernel/trace/trace_events_hist.c | 9 +++++++--
>> 1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/trace/trace_events_hist.c
>> b/kernel/trace/trace_events_hist.c
>> index ad7419e24055..900b06fa8505 100644
>> --- a/kernel/trace/trace_events_hist.c
>> +++ b/kernel/trace/trace_events_hist.c
>> @@ -5702,8 +5702,10 @@ static int event_hist_open(struct inode *inode,
>> struct file *file)
>> /* Clear private_data to avoid warning in single_open() */
>> file->private_data = NULL;
>> ret = single_open(file, hist_show, hist_file);
>> - if (ret)
>> + if (ret) {
>> kfree(hist_file);
>> + tracing_release_file_tr(inode, file);
>> + }
>
> Hmm, this function has a couple more error path exits after taking the
> ref count. If this is to be fixed, let's fix it completely. Each of
> those error paths need to call tracing_release_file_tr().
>
> -- Steve
Oops, I got it. The v2 is coming soon. Thanks a lot.
-- Tengda
>
>
>>
>> return ret;
>> }
>> @@ -5979,7 +5981,10 @@ static int event_hist_debug_open(struct inode *inode,
>> struct file *file)
>>
>> /* Clear private_data to avoid warning in single_open() */
>> file->private_data = NULL;
>> - return single_open(file, hist_debug_show, file);
>> + ret = single_open(file, hist_debug_show, file);
>> + if (ret)
>> + tracing_release_file_tr(inode, file);
>> + return ret;
>> }
>>
>> const struct file_operations event_hist_debug_fops = {
