linux-kernel - Re: [PATCH v2 6/7] mm: add assertion for VMA count limit

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

Message-ID: <eb7820ed-3351-4cb5-8341-d6a48ed7746f@redhat.com>
Date: Wed, 17 Sep 2025 15:44:27 +0200
From: David Hildenbrand <david@...hat.com>
To: Kalesh Singh <kaleshsingh@...gle.com>, akpm@...ux-foundation.org,
 minchan@...nel.org, lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com,
 rppt@...nel.org, pfalcato@...e.de
Cc: kernel-team@...roid.com, android-mm@...gle.com,
 Alexander Viro <viro@...iv.linux.org.uk>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 Kees Cook <kees@...nel.org>, Vlastimil Babka <vbabka@...e.cz>,
 Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
 Steven Rostedt <rostedt@...dmis.org>, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
 Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>, Ben Segall
 <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
 Valentin Schneider <vschneid@...hat.com>, Jann Horn <jannh@...gle.com>,
 Shuah Khan <shuah@...nel.org>, linux-kernel@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
 linux-trace-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 6/7] mm: add assertion for VMA count limit

On 15.09.25 18:36, Kalesh Singh wrote:
> Building on the vma_count helpers, add a VM_WARN_ON_ONCE() to detect
> cases where the VMA count exceeds the sysctl_max_map_count limit.
> 
> This check will help catch future bugs or regressions where
> the VMAs are allocated exceeding the limit.
> 
> The warning is placed in the main vma_count_*() helpers, while the
> internal *_nocheck variants bypass it. _nocheck helpers are used to
> ensure that the assertion does not trigger a false positive in
> the legitimate case of a temporary VMA increase past the limit
> by a VMA split in munmap().
> 
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
> Cc: Mike Rapoport <rppt@...nel.org>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Pedro Falcato <pfalcato@...e.de>
> Signed-off-by: Kalesh Singh <kaleshsingh@...gle.com>
> ---
> 
> Changes in v2:
>    - Add assertions if exceeding max_vma_count limit, per Pedro
> 
>   include/linux/mm.h               | 12 ++++++--
>   mm/internal.h                    |  1 -
>   mm/vma.c                         | 49 +++++++++++++++++++++++++-------
>   tools/testing/vma/vma_internal.h |  7 ++++-
>   4 files changed, 55 insertions(+), 14 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 8bad1454984c..3a3749d7015c 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4219,19 +4219,27 @@ static inline bool snapshot_page_is_faithful(const struct page_snapshot *ps)
>   
>   void snapshot_page(struct page_snapshot *ps, const struct page *page);
>   
> +int vma_count_remaining(const struct mm_struct *mm);
> +
>   static inline void vma_count_init(struct mm_struct *mm)
>   {
>   	ACCESS_PRIVATE(mm, __vma_count) = 0;
>   }
>   
> -static inline void vma_count_add(struct mm_struct *mm, int nr_vmas)
> +static inline void __vma_count_add_nocheck(struct mm_struct *mm, int nr_vmas)
>   {
>   	ACCESS_PRIVATE(mm, __vma_count) += nr_vmas;
>   }
>   
> +static inline void vma_count_add(struct mm_struct *mm, int nr_vmas)
> +{
> +	VM_WARN_ON_ONCE(!vma_count_remaining(mm));

Can't that fire when changing the max count from user space at just the 
wrong time?

I assume we'll have to tolerated that and might just want to drop this 
patch from the series.

-- 
Cheers

David / dhildenb