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

[Yongqiang Liu]

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
> .