linux-kernel - [PATCH] fs: romfs: Fix potential uninitialized memory leak

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Message-ID:
 <PH7PR20MB5925B0893BC44476B0D2E993BF712@PH7PR20MB5925.namprd20.prod.outlook.com>
Date: Thu, 18 Jan 2024 15:14:12 +0800
From: Fullway Wang <fullwaywang@...look.com>
To: jannh@...gle.com,
	akpm@...ux-foundation.org
Cc: dhowells@...hat.com,
	linux-kernel@...r.kernel.org,
	fullwaywang@...cent.com,
	Fullway Wang <fullwaywang@...look.com>
Subject: [PATCH] fs: romfs: Fix potential uninitialized memory leak

romfs_dev_read() fetches a caller-supplied number of bytes from the
backing device in an all-or-nothing manner.

Commit bcf85fc fixed CVE-2020-29371, which exposed the bug when
the requested length crossed the filesystem size limit, the number
of bytes to requested was truncated. However, in romfs_readdir()
in super.c, the requested number is firstly truncated with
romfs_dev_strnlen() then passed to romfs_dev_read(), leaving
the bug exploitable still.

Fix this by returning an error code instead of changing the length
in romfs_dev_strnlen() when the read might go beyond the end of
the filesystem.

Signed-off-by: Fullway Wang <fullwaywang@...look.com>
---
 fs/romfs/storage.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/fs/romfs/storage.c b/fs/romfs/storage.c
index b57b3ffcbc32..e0e4ecca4e65 100644
--- a/fs/romfs/storage.c
+++ b/fs/romfs/storage.c
@@ -240,10 +240,8 @@ ssize_t romfs_dev_strnlen(struct super_block *sb,
 	size_t limit;

 	limit = romfs_maxsize(sb);
-	if (pos >= limit)
+	if (pos >= limit || buflen > limit - pos)
 		return -EIO;
-	if (maxlen > limit - pos)
-		maxlen = limit - pos;

 #ifdef CONFIG_ROMFS_ON_MTD
 	if (sb->s_mtd)
-- 
2.39.3 (Apple Git-145)