linux-kernel - [PATCH] ocfs2: validate i_refcount

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Message-ID: <20251208084407.3021466-1-kartikey406@gmail.com>
Date: Mon,  8 Dec 2025 14:14:07 +0530
From: Deepanshu Kartikey <kartikey406@...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,
	Deepanshu Kartikey <kartikey406@...il.com>,
	syzbot+6d832e79d3efe1c46743@...kaller.appspotmail.com
Subject: [PATCH] ocfs2: validate i_refcount_loc when refcount flag is set

Add validation in ocfs2_validate_inode_block() to check that if an
inode has OCFS2_HAS_REFCOUNT_FL set, it must also have a valid
i_refcount_loc. A corrupted filesystem image can have this inconsistent
state, which later triggers a BUG_ON in ocfs2_remove_refcount_tree()
when the inode is being wiped during unlink.

Catch this corruption early during inode validation to fail gracefully
instead of crashing the kernel.

Reported-by: syzbot+6d832e79d3efe1c46743@...kaller.appspotmail.com
Tested-by: syzbot+6d832e79d3efe1c46743@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6d832e79d3efe1c46743
Signed-off-by: Deepanshu Kartikey <kartikey406@...il.com>
---
 fs/ocfs2/inode.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index 78f81950c9ee..dd56407fc056 100644
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -1484,6 +1484,13 @@ int ocfs2_validate_inode_block(struct super_block *sb,
 		goto bail;
 	}
 
+	if ((di->i_dyn_features & cpu_to_le16(OCFS2_HAS_REFCOUNT_FL)) &&
+	    !di->i_refcount_loc) {
+		rc = ocfs2_error(sb, "Invalid dinode #%llu: refcount flag set but i_refcount_loc is zero\n",
+		      (unsigned long long)bh->b_blocknr);
+		goto bail;
+	}
+
 	rc = 0;
 
 bail:
-- 
2.43.0