Re: [PATCH v2] maccess: fix strncpy_from_user_nofault empty string handling

[Mykyta Yatsenko <mykyta.yatsenko5@gmail.com>]

On 4/23/25 14:59, Steven Rostedt wrote:
> On Wed, 23 Apr 2025 12:37:46 +0100
> Mykyta Yatsenko <mykyta.yatsenko5@gmail.com> wrote:
>
>>> Does this fix any known runtime issue?  If so, please fully describe this?
>> Not that I'm aware of. The issue could be found when trying to copy empty
>> user space string in BPF program (and relying on return value).There are
>> some usage of
>> `strncpy_from_user_nofault` in tracing subsystem, but I'm not sure how to
>> hit those code paths.
>>>   
> Although your patch found a bug in the tracing subsystem, this wasn't the
> cause. It only cared if the read faulted or not. It was incorrectly
> checking for zero as non fault when in reality, it needed to check >= 0.
>
> With that fixed, it should work the same with or without this patch.
>
> -- Steve
Sure, I had in mind usages from trace_probe_kernel.h,
namely fetch_store_string_user, fetch_store_string, having a second look,
it appears these only used in trace_events_synth.c, and we are good there.