From cd7c3563a98fe8c984463d83772e518cb7e68356 Mon Sep 17 00:00:00 2001 From: Joseph Qi Date: Sat, 24 Oct 2026 23:10:12 +0800 Subject: [PATCH] ocfs2: do not read the entry array of an empty xattr block ocfs2_cp_xattr_block_to_bucket() sizes the name and value area it has to carry over from the block's last entry, so an empty block makes it read xh_entries[-1]. That lands on the header, where xe_name_offset overlaps xh_name_value_len, and block storage never maintains that field, so it reads as 0 and the copy runs from the header to the end of the block. The bucket that comes out has xh_count 0 but a name_value_len of blocksize less the header, and a matching xh_free_start that claims those bytes are in use -- nearly the whole bucket with the common 4K block size -- while the last block of the bucket holds a copy of the old block's bytes. Nothing but a trace event reads xh_name_value_len, the copied bytes came from the same inode and were wiped before the entry was removed, and ocfs2_defrag_xattr_bucket() recomputes xh_free_start, so this corrupts the header rather than leaking anything. Leave the bucket empty instead, carrying over the hash the block was keyed by, since ocfs2_add_new_xattr_bucket() and ocfs2_xattr_bucket_find() both read xh_entries[0] of an empty bucket. That read is the exception ocfs2_xa_remove_entry() documents rather than a new out of bounds access. A block reaches the conversion empty when truncating an external value back fails partway through: the "reusing" and "overwriting" callers of ocfs2_xa_cleanup_value_truncate() remove the entry without setting ctxt->set_abort, so ocfs2_xattr_block_set() sees a plain -ENOSPC and converts. The "growing" caller does set it, and the block form makes a single attempt with no defragment and retry in between, so that is the only route here. Link: https://lore.kernel.org/20261024151012.1059683-7-joseph.qi@linux.alibaba.com Fixes: 012255961c9e ("ocfs2: Enable xattr set in index btree") Signed-off-by: Joseph Qi Signed-off-by: Andrew Morton Cc: Heming Zhao Cc: Mark Fasheh Cc: Joel Becker Cc: --- fs/ocfs2/xattr.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c index 822b1e9c3ba2..ac41653e59f5 100644 --- a/fs/ocfs2/xattr.c +++ b/fs/ocfs2/xattr.c @@ -4704,6 +4704,21 @@ static void ocfs2_cp_xattr_block_to_bucket(struct inode *inode, for (i = 0; i < blks; i++) memset(bucket_block(bucket, i), 0, blocksize); + /* + * An empty block has no names or values to carry over, and the + * xh_entries[count - 1] below would be xh_entries[-1]. Leave the + * bucket empty, but carry over the hash ocfs2_xa_remove_entry() left + * in the block's xh_entries[0] so that the bucket still holds the key + * it is looked up by. + */ + if (!count) { + xh->xh_num_buckets = cpu_to_le16(1); + xh->xh_free_start = cpu_to_le16(OCFS2_XATTR_BUCKET_SIZE); + xh->xh_entries[0].xe_name_hash = + xb_xh->xh_entries[0].xe_name_hash; + return; + } + /* * Since the xe_name_offset is based on ocfs2_xattr_header, * there is a offset change corresponding to the change of