linux-kernel - [PATCH] ntfs3: Fix attr_punch_hole() null pointer derenference

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Message-Id: <20220815110712.36982-1-zahavi.alon@gmail.com>
Date:   Mon, 15 Aug 2022 14:07:12 +0300
From:   Alon Zahavi <zahavi.alon@...il.com>
To:     almaz.alexandrovich@...agon-software.com, ntfs3@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Cc:     Alon Zahavi <zahavi.alon@...il.com>,
        Tal Lossos <tallossos@...il.com>
Subject: [PATCH] ntfs3: Fix attr_punch_hole() null pointer derenference

From: Alon Zahavi <zahavi.alon@...il.com>

The bug occours due to a misuse of `attr` variable instead of `attr_b`.
`attr` is being initialized as NULL, then being derenfernced
as `attr->res.data_size`.

This bug causes a crash of the ntfs3 driver itself,
If compiled directly to the kernel, it crashes the whole system.

Signed-off-by: Alon Zahavi <zahavi.alon@...il.com>
Co-developed-by: Tal Lossos <tallossos@...il.com>
Signed-off-by: Tal Lossos <tallossos@...il.com>
---
 fs/ntfs3/attrib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ntfs3/attrib.c b/fs/ntfs3/attrib.c
index e8c00dda42ad..4e74bc8f01ed 100644
--- a/fs/ntfs3/attrib.c
+++ b/fs/ntfs3/attrib.c
@@ -1949,7 +1949,7 @@ int attr_punch_hole(struct ntfs_inode *ni, u64 vbo, u64 bytes, u32 *frame_size)
 		return -ENOENT;
 
 	if (!attr_b->non_res) {
-		u32 data_size = le32_to_cpu(attr->res.data_size);
+		u32 data_size = le32_to_cpu(attr_b->res.data_size);
 		u32 from, to;
 
 		if (vbo > data_size)
-- 
2.25.1