* [PATCH] mm/folio-compact: fix potential NULL pointer in pagecache_get_page
@ 2022-07-27 6:46 Yongqiang Liu
2022-07-27 11:40 ` William Kucharski
2022-07-27 13:29 ` Matthew Wilcox
0 siblings, 2 replies; 4+ messages in thread
From: Yongqiang Liu @ 2022-07-27 6:46 UTC (permalink / raw)
To: willy, dhowells, akpm, linux-mm, linux-kernel
Cc: zhangxiaoxu5, liuyongqiang13, yanaijie, vbabka, wangkefeng.wang
When __filemap_get_folio() failed and returned NULL, we would
get a NULL pointer dereference in pagecache_get_page.
Fixes: 3f0c6a07fee6 ("mm/filemap: Add filemap_get_folio")
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>
Cc: <stable@vger.kernel.org> # 5.16
---
mm/folio-compat.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/mm/folio-compat.c b/mm/folio-compat.c
index 20bc15b57d93..7b21393480e0 100644
--- a/mm/folio-compat.c
+++ b/mm/folio-compat.c
@@ -124,7 +124,9 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
struct folio *folio;
folio = __filemap_get_folio(mapping, index, fgp_flags, gfp);
- if ((fgp_flags & FGP_HEAD) || !folio || xa_is_value(folio))
+ if (!folio)
+ return NULL;
+ if ((fgp_flags & FGP_HEAD) || xa_is_value(folio))
return &folio->page;
return folio_file_page(folio, index);
}
--
2.25.1
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] mm/folio-compact: fix potential NULL pointer in pagecache_get_page
2022-07-27 6:46 [PATCH] mm/folio-compact: fix potential NULL pointer in pagecache_get_page Yongqiang Liu
@ 2022-07-27 11:40 ` William Kucharski
2022-07-28 1:36 ` Yongqiang Liu
2022-07-27 13:29 ` Matthew Wilcox
1 sibling, 1 reply; 4+ messages in thread
From: William Kucharski @ 2022-07-27 11:40 UTC (permalink / raw)
To: Yongqiang Liu
Cc: Matthew Wilcox, dhowells, akpm, linux-mm, linux-kernel,
zhangxiaoxu5, yanaijie, vbabka, wangkefeng.wang
This isn't a NULL pointer dereference; returning &(0->page) is completely legal
as was discussed regarding this exact code back in April:
https://lore.kernel.org/lkml/YmfgqKcMmstgfz+0@casper.infradead.org/
> On Jul 27, 2022, at 12:46 AM, Yongqiang Liu <liuyongqiang13@huawei.com> wrote:
>
> When __filemap_get_folio() failed and returned NULL, we would
> get a NULL pointer dereference in pagecache_get_page.
>
> Fixes: 3f0c6a07fee6 ("mm/filemap: Add filemap_get_folio")
> Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>
> Cc: <stable@vger.kernel.org> # 5.16
> ---
> mm/folio-compat.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/mm/folio-compat.c b/mm/folio-compat.c
> index 20bc15b57d93..7b21393480e0 100644
> --- a/mm/folio-compat.c
> +++ b/mm/folio-compat.c
> @@ -124,7 +124,9 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
> struct folio *folio;
>
> folio = __filemap_get_folio(mapping, index, fgp_flags, gfp);
> - if ((fgp_flags & FGP_HEAD) || !folio || xa_is_value(folio))
> + if (!folio)
> + return NULL;
> + if ((fgp_flags & FGP_HEAD) || xa_is_value(folio))
> return &folio->page;
> return folio_file_page(folio, index);
> }
> --
> 2.25.1
>
>
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH] mm/folio-compact: fix potential NULL pointer in pagecache_get_page
2022-07-27 11:40 ` William Kucharski
@ 2022-07-28 1:36 ` Yongqiang Liu
0 siblings, 0 replies; 4+ messages in thread
From: Yongqiang Liu @ 2022-07-28 1:36 UTC (permalink / raw)
To: William Kucharski
Cc: Matthew Wilcox, dhowells, akpm, linux-mm, linux-kernel,
zhangxiaoxu5, yanaijie, vbabka, wangkefeng.wang
Understood, thanks for your explanation :)
在 2022/7/27 19:40, William Kucharski 写道:
> This isn't a NULL pointer dereference; returning &(0->page) is completely legal
> as was discussed regarding this exact code back in April:
>
> https://lore.kernel.org/lkml/YmfgqKcMmstgfz+0@casper.infradead.org/
>
>> On Jul 27, 2022, at 12:46 AM, Yongqiang Liu <liuyongqiang13@huawei.com> wrote:
>>
>> When __filemap_get_folio() failed and returned NULL, we would
>> get a NULL pointer dereference in pagecache_get_page.
>>
>> Fixes: 3f0c6a07fee6 ("mm/filemap: Add filemap_get_folio")
>> Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>
>> Cc: <stable@vger.kernel.org> # 5.16
>> ---
>> mm/folio-compat.c | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/folio-compat.c b/mm/folio-compat.c
>> index 20bc15b57d93..7b21393480e0 100644
>> --- a/mm/folio-compat.c
>> +++ b/mm/folio-compat.c
>> @@ -124,7 +124,9 @@ struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
>> struct folio *folio;
>>
>> folio = __filemap_get_folio(mapping, index, fgp_flags, gfp);
>> - if ((fgp_flags & FGP_HEAD) || !folio || xa_is_value(folio))
>> + if (!folio)
>> + return NULL;
>> + if ((fgp_flags & FGP_HEAD) || xa_is_value(folio))
>> return &folio->page;
>> return folio_file_page(folio, index);
>> }
>> --
>> 2.25.1
>>
>>
> .
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] mm/folio-compact: fix potential NULL pointer in pagecache_get_page
2022-07-27 6:46 [PATCH] mm/folio-compact: fix potential NULL pointer in pagecache_get_page Yongqiang Liu
2022-07-27 11:40 ` William Kucharski
@ 2022-07-27 13:29 ` Matthew Wilcox
1 sibling, 0 replies; 4+ messages in thread
From: Matthew Wilcox @ 2022-07-27 13:29 UTC (permalink / raw)
To: Yongqiang Liu
Cc: dhowells, akpm, linux-mm, linux-kernel, zhangxiaoxu5, yanaijie,
vbabka, wangkefeng.wang
On Wed, Jul 27, 2022 at 06:46:21AM +0000, Yongqiang Liu wrote:
> When __filemap_get_folio() failed and returned NULL, we would
> get a NULL pointer dereference in pagecache_get_page.
No we wouldn't.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2022-07-27 6:46 [PATCH] mm/folio-compact: fix potential NULL pointer in pagecache_get_page Yongqiang Liu
2022-07-27 11:40 ` William Kucharski
2022-07-28 1:36 ` Yongqiang Liu
2022-07-27 13:29 ` Matthew Wilcox
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