linux-kernel - [RFC RFT PATCH] ocfs2: Invalidate inode if i

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Message-ID: <20251022222752.46758-2-eraykrdg1@gmail.com>
Date: Thu, 23 Oct 2025 01:27:53 +0300
From: Ahmet Eray Karadag <eraykrdg1@...il.com>
To: mark@...heh.com,
	jlbec@...lplan.org,
	joseph.qi@...ux.alibaba.com
Cc: ocfs2-devel@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	david.hunter.linux@...il.com,
	skhan@...uxfoundation.org,
	Ahmet Eray Karadag <eraykrdg1@...il.com>,
	syzbot+55c40ae8a0e5f3659f2b@...kaller.appspotmail.com,
	Albin Babu Varghese <albinbabuvarghese20@...il.com>
Subject: [RFC RFT PATCH] ocfs2: Invalidate inode if i_mode is zero after block read

A panic occurs in ocfs2_unlink due to WARN_ON(inode->i_nlink == 0) when
handling a corrupted inode with i_mode=0 and i_nlink=0 in memory.

This "zombie" inode is created because ocfs2_read_locked_inode proceeds
even after ocfs2_validate_inode_block successfully validates a block
that structurally looks okay (passes checksum, signature etc.) but
contains semantically invalid data (specifically i_mode=0). The current
validation function doesn't check for i_mode being zero.

This results in an in-memory inode with i_mode=0 being added to the VFS
cache, which later triggers the panic during unlink.

Prevent this by adding an explicit check for i_mode == 0 within
ocfs2_validate_inode_block. If i_mode is zero, return -EFSCORRUPTED to signal
corruption. This causes the caller (ocfs2_read_locked_inode) to invoke
make_bad_inode(), correctly preventing the zombie inode from entering
the cache.

---
[RFC]:
The current fix handles i_mode=0 corruption detected during inode read
by returning -EFSCORRUPTED from ocfs2_validate_inode_block, which leads to
make_bad_inode() being called, preventing the corrupted inode from
entering the cache. This approach avoids immediately forcing the entire
filesystem read-only, assuming the corruption might be localized to
this inode.

Is this less aggressive error handling strategy appropriate for i_mode=0
corruption? Or is this condition considered severe enough that we *should*
explicitly call ocfs2_error() within the validation function to guarantee
the filesystem is marked read-only immediately upon detection?
Feedback and testing on the correct severity assessment and error
handling for this type of corruption would be appreciated.
---

Reported-by: syzbot+55c40ae8a0e5f3659f2b@...kaller.appspotmail.com
Fixes: https://syzkaller.appspot.com/bug?extid=55c40ae8a0e5f3659f2b
Co-developed-by: Albin Babu Varghese <albinbabuvarghese20@...il.com>
Signed-off-by: Albin Babu Varghese <albinbabuvarghese20@...il.com>
Signed-off-by: Ahmet Eray Karadag <eraykrdg1@...il.com>
---
 fs/ocfs2/inode.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index 14bf440ea4df..d4142ff9ce65 100644
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -1456,6 +1456,12 @@ int ocfs2_validate_inode_block(struct super_block *sb,
 		goto bail;
 	}
 
+	if (unlikely(le16_to_cpu(di->i_mode) == 0)) {
+		mlog(ML_ERROR, "Invalid dinode #%llu: i_mode is zero!\n",
+                           (unsigned long long)bh->b_blocknr);
+		rc = -EFSCORRUPTED;
+		goto bail;
+	}
 	/*
 	 * Errors after here are fatal.
 	 */
-- 
2.43.0