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
