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Message-ID: <2a3d6cd7-ee80-4a60-939c-129e7d3e169d@redhat.com>
Date: Thu, 7 Nov 2024 13:04:31 +0100
From: David Hildenbrand <david@...hat.com>
To: Qiu-ji Chen <chenqiuji666@...il.com>, akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, baijiaju1990@...il.com,
stable@...r.kernel.org
Subject: Re: [PATCH] mm: fix a possible null pointer dereference in
setup_zone_pageset()
On 07.11.24 12:34, Qiu-ji Chen wrote:
> The function call alloc_percpu() returns a pointer to the memory address,
> but it hasn't been checked. Our static analysis tool indicates that null
> pointer dereference may exist in pointer zone->per_cpu_pageset. It is
> always safe to judge the null pointer before use.
>
> Signed-off-by: Qiu-ji Chen <chenqiuji666@...il.com>
> Cc: stable@...r.kernel.org
> Fixes: 9420f89db2dd ("mm: move most of core MM initialization to mm/mm_init.c")
> ---
> mm/page_alloc.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 8afab64814dc..5deae1193dc3 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5703,8 +5703,14 @@ void __meminit setup_zone_pageset(struct zone *zone)
> /* Size may be 0 on !SMP && !NUMA */
> if (sizeof(struct per_cpu_zonestat) > 0)
> zone->per_cpu_zonestats = alloc_percpu(struct per_cpu_zonestat);
> + if (!zone->per_cpu_pageset)
> + return;
Don't we initialize this for all with &boot_pageset? How could this ever
happen?
>
> zone->per_cpu_pageset = alloc_percpu(struct per_cpu_pages);
> + if (!zone->per_cpu_pageset) {
> + free_percpu(zone->per_cpu_pageset);
> + return;
If it's NULL, we free it. Why?
> + }
> for_each_possible_cpu(cpu) {
> struct per_cpu_pages *pcp;
> struct per_cpu_zonestat *pzstats;
Also, how could core code ever recover if this function would return
early, leaving something partially initialized?
The missing NULL check is concerning, but looking into alloc_percpu() we
treat these as atomic allocations and would print a warning in case this
would ever happen. So likely it never really happens in practice.
I wonder if we simply want to leave it unmodified (IOW set to
&boot_pageset) in case the allocation fails. We'd already print a
warning in this unexpected scenario.
--
Cheers,
David / dhildenb
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