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.

Link: https://lkml.kernel.org/r/20251212055826.20929-1-kartikey406@gmail.com
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
Reported-by: syzbot+6d832e79d3efe1c46743@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=6d832e79d3efe1c46743
Tested-by: syzbot+6d832e79d3efe1c46743@syzkaller.appspotmail.com
Link: https://lore.kernel.org/all/20251208084407.3021466-1-kartikey406@gmail.com/T/
Link: https://lore.kernel.org/all/20251212045646.9988-1-kartikey406@gmail.com/T/
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Changwei Ge <gechangwei@live.cn>
Cc: Jun Piao <piaojun@huawei.com>
Cc: Heming Zhao <heming.zhao@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/fs/ocfs2/inode.c b/fs/ocfs2/inode.c
index b5fcc2725a2962a615904ed1b35747a2a2e57754..c95c998811ae54d1289a2bb0179a267df68f0307 100644 (file)
--- a/fs/ocfs2/inode.c
+++ b/fs/ocfs2/inode.c
@@ -1529,6 +1529,13 @@ int ocfs2_validate_inode_block(struct super_block *sb,
                }
        }
 
+       if ((le16_to_cpu(di->i_dyn_features) & OCFS2_HAS_REFCOUNT_FL) &&
+           !di->i_refcount_loc) {
+               rc = ocfs2_error(sb, "Inode #%llu has refcount flag but no i_refcount_loc\n",
+                               (unsigned long long)bh->b_blocknr);
+               goto bail;
+       }
+
        rc = 0;
 
 bail: