linux-kernel - Re: [patch 163/227] mm: madvise: skip unmapped vma holes passed to process

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <YjraNQkmtkLiv1yz@dhcp22.suse.cz>
Date:   Wed, 23 Mar 2022 09:28:37 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...ux-foundation.org>, vbabka@...e.cz,
        surenb@...gle.com, stable@...r.kernel.org, sfr@...b.auug.org.au,
        rientjes@...gle.com, nadav.amit@...il.com,
        quic_charante@...cinc.com, patches@...ts.linux.dev,
        linux-mm@...ck.org, mm-commits@...r.kernel.org,
        torvalds@...ux-foundation.org
Subject: Re: [patch 163/227] mm: madvise: skip unmapped vma holes passed to
 process_madvise

On Tue 22-03-22 17:24:58, Minchan Kim wrote:
> On Tue, Mar 22, 2022 at 02:46:48PM -0700, Andrew Morton wrote:
> > From: Charan Teja Kalla <quic_charante@...cinc.com>
> > Subject: mm: madvise: skip unmapped vma holes passed to process_madvise
> > 
> > The process_madvise() system call is expected to skip holes in vma passed
> > through 'struct iovec' vector list.  But do_madvise, which
> > process_madvise() calls for each vma, returns ENOMEM in case of unmapped
> > holes, despite the VMA is processed.
> > 
> > Thus process_madvise() should treat ENOMEM as expected and consider the
> > VMA passed to as processed and continue processing other vma's in the
> > vector list.  Returning -ENOMEM to user, despite the VMA is processed,
> > will be unable to figure out where to start the next madvise.
> > 
> > Link: https://lkml.kernel.org/r/4f091776142f2ebf7b94018146de72318474e686.1647008754.git.quic_charante@quicinc.com
> 
> I thought it was still under discussion and Charan will post next
> version along with previous patch
> "mm: madvise: return correct bytes advised with process_madvise"
> 
> https://lore.kernel.org/linux-mm/7207b2f5-6b3e-aea4-aa1b-9c6d849abe34@quicinc.com/

Yes, I am not even sure the new semantic is sensible[1]. We should discuss
that and see all the consequences. Changing the semantic of an existing
syscall is always tricky going back and forth is even worse.
-- 
Michal Hocko
SUSE Labs