Re: [PATCH] mm/folio-compact: fix potential NULL pointer in pagecache_get_page

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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@xxxxxxxxxxxxxxxxxxxx/

On Jul 27, 2022, at 12:46 AM, Yongqiang Liu <liuyongqiang13@xxxxxxxxxx> 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@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 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


.




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