[PATCH] fs/ntfs3: fix out-of-bounds read of INDEX_ROOT in reparse/objid init

[Weiming Shi <bestswngs@gmail.com>]

From: Weiming Wu <weiming3@asu.edu>

ntfs_reparse_init() and ntfs_objid_init() parse the index root of the
$Extend/$Reparse and $Extend/$ObjId metafiles (the INDEX_ROOT attributes
named $R and $O). They read its type and rule fields through
resident_data(), which does not check that the resident attribute is
large enough to hold them.

mi_enum_attr() accepts a resident attribute with data_off == asize and
data_size == 0. For such an attribute placed last in its MFT record,
resident_data() returns a pointer to the end of the record_size buffer,
so reading root->type / root->rule reads past the allocation.

Use resident_data_ex(attr, sizeof(struct INDEX_ROOT)) and bail out when
it returns NULL, as ntfs_security_init() already does for $SDH / $SII.

The attribute is only parsed while mounting a crafted image, so this
needs CAP_SYS_ADMIN.

 BUG: KASAN: slab-out-of-bounds in ntfs_reparse_init (fs/ntfs3/fsntfs.c:2306)
 Read of size 4 at addr ffff88801219dc00 by task mount
  ntfs_reparse_init (fs/ntfs3/fsntfs.c:2306)
  ntfs_fill_super (fs/ntfs3/super.c:1604)
  get_tree_bdev_flags (fs/super.c:1703)
  vfs_get_tree (fs/super.c:1758)
  path_mount (fs/namespace.c:4131)
  __x64_sys_mount (fs/namespace.c:4360)

Fixes: 82cae269cfa9 ("fs/ntfs3: Add initialization of super block")
Reported-by: Xiang Mei <xmei5@asu.edu>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
---
 fs/ntfs3/fsntfs.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/ntfs3/fsntfs.c b/fs/ntfs3/fsntfs.c
index d0434756029b6..42493a2da24ef 100644
--- a/fs/ntfs3/fsntfs.c
+++ b/fs/ntfs3/fsntfs.c
@@ -2302,8 +2302,8 @@ int ntfs_reparse_init(struct ntfs_sb_info *sbi)
 		goto out;
 	}
 
-	root_r = resident_data(attr);
-	if (root_r->type != ATTR_ZERO ||
+	root_r = resident_data_ex(attr, sizeof(struct INDEX_ROOT));
+	if (!root_r || root_r->type != ATTR_ZERO ||
 	    root_r->rule != NTFS_COLLATION_TYPE_UINTS) {
 		err = -EINVAL;
 		goto out;
@@ -2340,8 +2340,8 @@ int ntfs_objid_init(struct ntfs_sb_info *sbi)
 		goto out;
 	}
 
-	root = resident_data(attr);
-	if (root->type != ATTR_ZERO ||
+	root = resident_data_ex(attr, sizeof(struct INDEX_ROOT));
+	if (!root || root->type != ATTR_ZERO ||
 	    root->rule != NTFS_COLLATION_TYPE_UINTS) {
 		err = -EINVAL;
 		goto out;
-- 
2.43.0