Re: [PATCH RFC 0/2] Dynamically allocate memory to store task's full name

[Bhupesh Sharma]

Hi Kees,

On 3/18/25 9:21 PM, Kees Cook wrote:
> On Tue, Mar 18, 2025 at 04:49:28PM +0530, Bhupesh Sharma wrote:
> > On 3/15/25 1:13 PM, Andres Rodriguez wrote:
> > > On 3/14/25 14:25, Kees Cook wrote:
> > > > On Fri, Mar 14, 2025 at 10:57:13AM +0530, Bhupesh wrote:
> > > > > While working with user-space debugging tools which work especially
> > > > > on linux gaming platforms, I found that the task name is truncated due
> > > > > to the limitation of TASK_COMM_LEN.
> > > > >
> > > > > For example, currently running 'ps', the task->comm value of a long
> > > > > task name is truncated due to the limitation of TASK_COMM_LEN.
> > > > >       create_very_lon
> > > > >
> > > > > This leads to the names passed from userland via pthread_setname_np()
> > > > > being truncated.
> > > > So there have been long discussions about "comm", and it mainly boils
> > > > down to "leave it alone". For the /proc-scraping tools like "ps" and
> > > > "top", they check both "comm" and "cmdline", depending on mode. The more
> > > > useful (and already untruncated) stuff is in "cmdline", so I suspect it
> > > > may make more sense to have pthread_setname_np() interact with that
> > > > instead. Also TASK_COMM_LEN is basically considered userspace ABI at
> > > > this point and we can't sanely change its length without breaking the
> > > > world.
> > > Completely agree that comm is best left untouched. TASK_COMM_LEN is
> > > embedded into the kernel and the pthread ABI changes here should be
> > > avoided.
> > So, basically my approach _does not_ touch TASK_COMM_LEN at all. The normal
> > 'TASK_COMM_LEN' 16byte design remains untouched.
> > Which means that all the legacy / existing ABi which uses 'task->comm' and
> > hence are designed / written to handle 'TASK_COMM_LEN' 16-byte name,
> > continue to work as before using '/proc/$pid/task/$tid/comm'.
> >
> > This change-set only adds a _parallel_ dynamically allocated
> > 'task->full_name' which can be used by interested users via
> > '/proc/$pid/task/$tid/full_name'.
> I don't want to add this to all processes at exec time as the existing
> solution works for those processes: read /proc/$pid/cmdline.
>
> That said, adding another pointer to task_struct isn't to bad I guess,
> and it could be updated by later calls. Maybe by default it just points
> to "comm".
Sure.

> > I am fine with adding either '/proc/$pid/task/$tid/full_name' or
> > '/proc/$pid/task/$tid/debug_name' (actually both of these achieve the same).
> > The new / modified users (especially the debug applications you listed
> > above) can switch easily to using '/proc/$pid/task/$tid/full_name' instead
> > of ''/proc/$pid/task/$tid/comm'
> >
> > AFAIK we already achieved for the kthreads using d6986ce24fc00 ("kthread:
> > dynamically allocate memory to store kthread's full name"), which adds
> > 'full_name' in parallel to 'comm' for kthread names.
> If we do this for task_struct, we should remove "full_name" from kthread
> and generalize it for all processes.
Got it. Ok, let me rework the series so that we have a unified 
'full_name' inside 'task_struct' and have kthread use it as well.

I will send a v2 accordingly.

Thanks,
Bhupesh