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Date: Mon, 3 Jun 2024 18:07:39 +0200
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Subject: Re: [PATCH] mm/memory_hotplug: prevent accessing by index=-1
To: Anastasia Belova <abelova@astralinux.ru>
Cc: Oscar Salvador <osalvador@suse.de>,
 Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
 linux-kernel@vger.kernel.org, lvc-project@linuxtesting.org
References: <20240603112830.7432-1-abelova@astralinux.ru>
From: David Hildenbrand <david@redhat.com>
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In-Reply-To: <20240603112830.7432-1-abelova@astralinux.ru>
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On 03.06.24 13:28, Anastasia Belova wrote:
> nid may be equal to NUMA_NO_NODE=-1. Prevent accessing node_data
> array by invalid index with check for nid.
> 
> Found by Linux Verification Center (linuxtesting.org) with SVACE.
> 
> Fixes: e83a437faa62 ("mm/memory_hotplug: introduce "auto-movable" online policy")
> Signed-off-by: Anastasia Belova <abelova@astralinux.ru>
> ---
>   mm/memory_hotplug.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 431b1f6753c0..bb98ee8fe698 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -846,7 +846,7 @@ static bool auto_movable_can_online_movable(int nid, struct memory_group *group,
>   	unsigned long kernel_early_pages, movable_pages;
>   	struct auto_movable_group_stats group_stats = {};
>   	struct auto_movable_stats stats = {};
> -	pg_data_t *pgdat = NODE_DATA(nid);
> +	pg_data_t *pgdat = (nid != NUMA_NO_NODE) ? NODE_DATA(nid) : NULL;
>   	struct zone *zone;
>   	int i;


pgdat is never dereferenced when "nid == NUMA_NO_NODE".

NODE_DATA is defined as

arch/arm64/include/asm/mmzone.h:#define NODE_DATA(nid)          (node_data[(nid)])
arch/loongarch/include/asm/mmzone.h:#define NODE_DATA(nid)      (node_data[(nid)])
arch/mips/include/asm/mach-ip27/mmzone.h:#define NODE_DATA(n)           (&__node_data[(n)]->pglist)
arch/mips/include/asm/mach-loongson64/mmzone.h:#define NODE_DATA(n)             (__node_data[n])
arch/powerpc/include/asm/mmzone.h:#define NODE_DATA(nid)                (node_data[nid])
arch/riscv/include/asm/mmzone.h:#define NODE_DATA(nid)          (node_data[(nid)])
arch/s390/include/asm/mmzone.h:#define NODE_DATA(nid) (node_data[nid])
arch/sh/include/asm/mmzone.h:#define NODE_DATA(nid)             (node_data[nid])
arch/sparc/include/asm/mmzone.h:#define NODE_DATA(nid)          (node_data[nid])
arch/x86/include/asm/mmzone_32.h:#define NODE_DATA(nid) (node_data[nid])
arch/x86/include/asm/mmzone_64.h:#define NODE_DATA(nid)         (node_data[nid])

Regarding architectures that's actually support memory hotplug, this is pure pointer arithmetic.
(it is for mips as well, just less obvious)

So how is that a real problem? Do we have a reproducer?

-- 
Cheers,

David / dhildenb