[PATCH v2] ntfs: fix name offset validation in ntfs_non_resident_attr_value_is_valid

ntfs_attr_update_meta() performs memmove operations on attribute names
when converting between sparse and non-sparse attributes:

- Converting to sparse shifts the name forward by 8 bytes
  (name_offset + 8)
- Converting from sparse shifts the name backward by 8 bytes
  (name_offset - 8)

However, the validator does not check that name_offset is within safe
boundaries for these operations. A malicious MFT record could set
name_offset such that:

1. The name is positioned at the very end of a non-sparse attribute.
   Converting to sparse would shift the name forward by 8 bytes,
   writing beyond the attribute boundary.

2. The name overlaps with the mapping pairs, causing corruption during
   conversion.

Add validation to ensure:
- For named attributes, name_offset is within valid bounds
- Name does not extend beyond the attribute or overlap with mapping pairs
- For non-sparse attributes, name_end + 8 fits within attr_len to allow
  room for the forward shift when becoming sparse

Note: name_offset validation only applies when name_length != 0, as
unnamed attributes use name_offset = 0 which is valid.

Fixes: 7e2a1c554bc4 ("ntfs: Fix min_len for compressed/sparse attributes in ntfs_non_resident_attr_value_is_valid()")
Cc: [email protected]
Signed-off-by: Hongling Zeng <[email protected]>
---
Changes in v2:
- Read name_length directly as an 8-bit field instead of using
  le16_to_cpu().
- Restrict the name forward-shift bounds check to the same attribute
  types that can actually be converted by ntfs_attr_update_meta().
---
 fs/ntfs/attrib.c | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/fs/ntfs/attrib.c b/fs/ntfs/attrib.c
index d354c3b0fae1..ffd08633970a 100644
--- a/fs/ntfs/attrib.c
+++ b/fs/ntfs/attrib.c
@@ -693,6 +693,9 @@ static bool ntfs_non_resident_attr_value_is_valid(const struct attr_record *a)
 	u32 attr_len;
 	u32 min_len;
 	u16 mp_offset;
+	u16 name_offset;
+	u8 name_len;
+	u32 name_end;
 
 	attr_len = le32_to_cpu(a->length);
 	min_len = offsetof(struct attr_record, data.non_resident.initialized_size) +
@@ -706,7 +709,35 @@ static bool ntfs_non_resident_attr_value_is_valid(const struct attr_record *a)
 		return false;
 
 	mp_offset = le16_to_cpu(a->data.non_resident.mapping_pairs_offset);
-	return mp_offset >= min_len && mp_offset <= attr_len;
+	if (mp_offset < min_len || mp_offset > attr_len)
+		return false;
+
+	/*
+	 * Validate name_offset for named attributes.
+	 * may be zero for unnamed attributes.
+	 */
+	name_len = a->name_length;
+	if (name_len) {
+		name_offset = le16_to_cpu(a->name_offset);
+
+		if (name_offset < min_len || name_offset >= attr_len)
+			return false;
+
+		name_end = name_offset + name_len * sizeof(__le16);
+		if (name_end > attr_len || name_end > mp_offset)
+			return false;
+
+		/*
+		 * A normal non-resident attribute moves its name forward when
+		 * it is converted to a sparse attribute.
+		 */
+		if (!(a->flags & (ATTR_IS_SPARSE | ATTR_COMPRESSION_MASK)) &&
+		     name_end + 8 > attr_len)
+			return false;
+	}
+
+	return true;
+
 }
 
 static bool ntfs_attr_value_is_valid(struct ntfs_volume *vol,
-- 
2.25.1