linux-kernel - [PATCH] fs/ext4: Initialize new folios before use

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Message-Id: <20251223215855.2486271-1-kubik.bartlomiej@gmail.com>
Date: Tue, 23 Dec 2025 22:58:55 +0100
From: Bartlomiej Kubik <kubik.bartlomiej@...il.com>
To: tytso@....edu
Cc: adilger.kernel@...ger.ca,
	linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	david.hunter.linux@...il.com,
	skhan@...uxfoundation.org,
	khalid@...nel.org,
	linux-kernel-mentees@...ts.linux.dev,
	Bartlomiej Kubik <kubik.bartlomiej@...il.com>,
	syzbot+703d8a2cd20971854b06@...kaller.appspotmail.com
Subject: [PATCH] fs/ext4: Initialize new folios before use

KMSAN reports an uninitialized value in adiantum_crypt, created at
write_begin_get_folio(). New folios are allocated with the FGP_CREAT
flag and may be returned uninitialized. These uninitialized folios are
then used without proper initialization.

Fixes: b799474b9aeb ("mm/pagemap: add write_begin_get_folio() helper function")
Tested-by: syzbot+703d8a2cd20971854b06@...kaller.appspotmail.com
Reported-by: syzbot+703d8a2cd20971854b06@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=703d8a2cd20971854b06

Signed-off-by: Bartlomiej Kubik <kubik.bartlomiej@...il.com>
---
 include/linux/pagemap.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 31a848485ad9..31bbc8299e08 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -787,7 +787,8 @@ static inline struct folio *write_begin_get_folio(const struct kiocb *iocb,
                 fgp_flags |= FGP_DONTCACHE;

         return __filemap_get_folio(mapping, index, fgp_flags,
-                                   mapping_gfp_mask(mapping));
+				mapping_gfp_mask(mapping)|
+				__GFP_ZERO);
 }

 /**
--
2.39.5