Re: [PATCH 1/5] kprobes: Do not use local variable when creating debugfs file

Punit Agrawal
2021-06-10T23:33:06Z

Hi Masami,

Masami Hiramatsu <mhiramat@kernel.org> writes:

> On Wed, 9 Jun 2021 19:50:15 +0900
> Punit Agrawal <punitagrawal@gmail.com> wrote:
>
>> debugfs_create_file() takes a pointer argument that can be used during
>> file operation callbacks (accessible via i_private in the inode
>> structure). An obvious requirement is for the pointer to refer to
>> valid memory when used.
>>
>> When creating the debugfs file to dynamically enable / disable
>> kprobes, a pointer to local variable is passed to
>> debugfs_create_file(); which will go out of scope when the init
>> function returns. The reason this hasn't triggered random memory
>> corruption is because the pointer is not accessed during the debugfs
>> file callbacks.
>>
>> Fix the incorrect (and unnecessary) usage of local variable during
>> debugfs_file_create() by passing NULL instead.
>>
>
> Good catch! Since the enabled state is managed by the kprobes_all_disabled
> global variable, it is not needed.
>
> Fixes: bf8f6e5b3e51 ("Kprobes: The ON/OFF knob thru debugfs")
> Acked-by: Masami Hiramatsu <mhiramat@kernel.org>

Thanks a lot for reviewing the patches.

I am assuming the tags can be picked up when applying. Let me know if I
need to resend.

Thanks,
Punit

>
> Thank you!
>
>> Signed-off-by: Punit Agrawal <punitagrawal@gmail.com>
>> ---
>> kernel/kprobes.c | 3 +--
>> 1 file changed, 1 insertion(+), 2 deletions(-)
>>
>> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
>> index 745f08fdd7a6..fdb1ea2e963b 100644
>> --- a/kernel/kprobes.c
>> +++ b/kernel/kprobes.c
>> @@ -2816,13 +2816,12 @@ static const struct file_operations fops_kp = {
>> static int __init debugfs_kprobe_init(void)
>> {
>> struct dentry *dir;
>> - unsigned int value = 1;
>>
>> dir = debugfs_create_dir("kprobes", NULL);
>>
>> debugfs_create_file("list", 0400, dir, NULL, &kprobes_fops);
>>
>> - debugfs_create_file("enabled", 0600, dir, &value, &fops_kp);
>> + debugfs_create_file("enabled", 0600, dir, NULL, &fops_kp);
>>
>> debugfs_create_file("blacklist", 0400, dir, NULL,
>> &kprobe_blacklist_fops);
>> --
>> 2.30.2
>>