On Mon, Mar 15, 2021 at 03:24:01PM +0300, Vasily Averin wrote:

Unprivileged user inside memcg-limited container can create
non-accounted multi-page per-thread kernel objects for LDT

I have hard time parsing this commit message.

And I'm CCed only on patch 8 of what looks like a patchset.

And that patchset is not on lkml so I can't find the rest to read about
it, perhaps linux-mm.

/me goes and finds it on lore

I can see some bits and pieces, this, for example:

https://lore.kernel.org/linux-mm/05c448c7-d992-8d80-b423-b80bf5446d7c@virtuozzo.com/ (local)

 ( Btw, that version has your SOB and this patch doesn't even have a
   Signed-off-by. Next time, run your whole set through checkpatch please
   before sending. )

Now, this URL above talks about OOM, ok, that gets me close to the "why"
this patch.

From a quick look at the ldt.c code, we allow a single LDT struct per
mm. Manpage says so too:

DESCRIPTION
       modify_ldt()  reads  or  writes  the local descriptor table (LDT) for a process.
       The LDT is an array of segment descriptors that can be referenced by user  code.
       Linux  allows  processes  to configure a per-process (actually per-mm) LDT.

We allow

/* Maximum number of LDT entries supported. */
#define LDT_ENTRIES     8192

so there's an upper limit per mm.

Now, please explain what is this accounting for?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette