[PATCH v2 3/3] ntfs: check overflow when iterates ATTR_RECORDs

[Hawkins Jiawei <yin31149@gmail.com>]

Kernel will iterates over ATTR_RECORDs in mft record in ntfs_attr_find().
Because the ATTR_RECORDs are next to each other, kernel can get the next
ATTR_RECORD from end address of current ATTR_RECORD, through current
ATTR_RECORD length field.

The problem is that during iteration, when kernel calculates the end address
of current ATTR_RECORD, kernel may trigger an integer overflow bug in
executing `a = (ATTR_RECORD*)((u8*)a + le32_to_cpu(a->length))`. This
may wrap, leading to a forever iteration on 32bit systems.

This patch solves it by adding some checks on calculating end address
of current ATTR_RECORD during iteration.

Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/all/20220827105842.GM2030@kadam/
Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
---
v1->v2:
 * Add check bounds on ATTR_RECORD's length suggested
by Dan Carpenter.

 fs/ntfs/attrib.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/ntfs/attrib.c b/fs/ntfs/attrib.c
index cec4be2a2d23..a3865bc4a0c6 100644
--- a/fs/ntfs/attrib.c
+++ b/fs/ntfs/attrib.c
@@ -617,6 +617,14 @@ static int ntfs_attr_find(const ATTR_TYPE type, const ntfschar *name,
 			return -ENOENT;
 		if (unlikely(!a->length))
 			break;
+
+		/* check whether ATTR_RECORD's length wrap */
+		if ((u8 *)a + le32_to_cpu(a->length) < (u8 *)a)
+			break;
+		/* check whether ATTR_RECORD's length is within bounds */
+		if ((u8 *)a + le32_to_cpu(a->length) > mrec_end)
+			break;
+
 		if (a->type != type)
 			continue;
 		/*
-- 
2.25.1