[syzbot] [ntfs3?] WARNING in ni_rename

[Moon Hee Lee]

#syz test
From 7fa1f4b399c2d47d1ab301c2662f6a60c2098c45 Mon Sep 17 00:00:00 2001
From: Moon Hee Lee <moonhee.lee.ca@xxxxxxxxx>
Date: Tue, 8 Jul 2025 14:39:43 -0700
Subject: [PATCH] ntfs3: validate $BITMAP size when index blocks are present

Reject directories with allocated index blocks but zero-length $BITMAP,
as this indicates an inconsistent on-disk structure.

Signed-off-by: Moon Hee Lee <moonhee.lee.ca@xxxxxxxxx>
---
 fs/ntfs3/index.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/ntfs3/index.c b/fs/ntfs3/index.c
index 1bf2a6593dec..6d1bf890929d 100644
--- a/fs/ntfs3/index.c
+++ b/fs/ntfs3/index.c
@@ -1508,6 +1508,16 @@ static int indx_add_allocate(struct ntfs_index *indx, struct ntfs_inode *ni,
 			bmp_size = bmp_size_v = le32_to_cpu(bmp->res.data_size);
 		}
 
+		/*
+		 * Index blocks exist, but $BITMAP has zero valid bits.
+		 * This implies an on-disk corruption and must be rejected.
+		 */
+		if (in->name == I30_NAME &&
+		    unlikely(bmp_size_v == 0 && indx->alloc_run.count)) {
+			err = -EINVAL;
+			goto out1;
+		}
+
 		bit = bmp_size << 3;
 	}
 
-- 
2.43.0