[PATCH v2] ntfs3: Add bounds checking to mi_enum_attr()

[lei lu <llfamsec@gmail.com>]

Added bounds checking to make sure that every attr don't stray beyond
valid memory region.

Signed-off-by: lei lu <llfamsec@gmail.com>
---
 fs/ntfs3/record.c | 23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/fs/ntfs3/record.c b/fs/ntfs3/record.c
index 6aa3a9d44df1..973e2a371bc2 100644
--- a/fs/ntfs3/record.c
+++ b/fs/ntfs3/record.c
@@ -223,28 +223,19 @@ struct ATTRIB *mi_enum_attr(struct mft_inode *mi, struct ATTRIB *attr)
 		prev_type = 0;
 		attr = Add2Ptr(rec, off);
 	} else {
-		/* Check if input attr inside record. */
+		/*
+		 * We don't need to check previous attr here. There is
+		 * a bounds checking in the previous round.
+		 */
 		off = PtrOffset(rec, attr);
-		if (off >= used)
-			return NULL;
 
 		asize = le32_to_cpu(attr->size);
-		if (asize < SIZEOF_RESIDENT) {
-			/* Impossible 'cause we should not return such attribute. */
-			return NULL;
-		}
-
-		/* Overflow check. */
-		if (off + asize < off)
-			return NULL;
 
 		prev_type = le32_to_cpu(attr->type);
 		attr = Add2Ptr(attr, asize);
 		off += asize;
 	}
 
-	asize = le32_to_cpu(attr->size);
-
 	/* Can we use the first field (attr->type). */
 	if (off + 8 > used) {
 		static_assert(ALIGN(sizeof(enum ATTR_TYPE), 8) == 8);
@@ -265,6 +256,12 @@ struct ATTRIB *mi_enum_attr(struct mft_inode *mi, struct ATTRIB *attr)
 	if (t32 < prev_type)
 		return NULL;
 
+	asize = le32_to_cpu(attr->size);
+	if (asize < SIZEOF_RESIDENT) {
+		/* Impossible 'cause we should not return such attribute. */
+		return NULL;
+	}
+
 	/* Check overflow and boundary. */
 	if (off + asize < off || off + asize > used)
 		return NULL;
-- 
2.34.1