linux-kernel - [PATCH] mm/filemap: Fix NULL pointer dereference in pagecache_get

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Date:   Tue, 26 Apr 2022 16:25:48 +0800
From:   Wan Jiabing <wanjiabing@...o.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Howells <dhowells@...hat.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Wan Jiabing <wanjiabing@...o.com>
Subject: [PATCH] mm/filemap: Fix NULL pointer dereference in pagecache_get_page

Fix following coccicheck error:
mm/folio-compat.c:128:17-21: ERROR: folio is NULL but dereferenced.

'folio' would be NULL when getting a reference to a folio failed.
Add a NULL check before dereferring 'folio'.

Fixes: 3f0c6a07fee6 ("mm/filemap: Add filemap_get_folio")
Signed-off-by: Wan Jiabing <wanjiabing@...o.com>
---
 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 46fa179e32fb..54b17c1246c4 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);
 }
-- 
2.35.3