From 7133a0d0954c109f1764ebf8ab32d7e757a6c587 Mon Sep 17 00:00:00 2001 From: Joseph Qi Date: Sat, 24 Oct 2026 23:10:11 +0800 Subject: [PATCH] ocfs2: do not index before the entry array when dividing an empty bucket ocfs2_divide_xattr_bucket() appends an empty bucket carrying a sentinel hash when the source bucket has no divide position, taking that hash from xh_entries[start - 1]. ocfs2_xattr_find_divide_pos() returns count when every entry shares one hash, and its loop does not run at all for count < 2, so an empty bucket comes back with start == count == 0 and the read is xh_entries[-1]. That is outside the __counted_by_le(xh_count) bounds of xh_entries[] and lands on the header, so the value picked up is xh_count | xh_free_start << 16. One above it is written into the new bucket's xh_entries[0] and committed, which leaves a bucket whose first hash does not follow the bucket before it. ocfs2_xattr_bucket_find() binary searches on xh_entries[0], so the broken key hides the range the sentinel was meant to cover: getxattr() answers -ENODATA for an attribute that is stored, and an insert can go to the wrong bucket and leave two copies of a name. The cross cluster divide hands the same value back as a tree record's e_cpos, which then claims a hash range it does not cover. Read xh_entries[0] instead. The branch is only reached when every entry shares one hash, so for a non-empty bucket it holds the same value, and for an empty one it is the slot that carries the bucket key. An empty bucket reaches the divide from ocfs2_check_xattr_bucket_collision(), which reports no collision for one, through ocfs2_add_new_xattr_bucket() and ocfs2_extend_xattr_bucket(). It does not take a failed set to get there: a divide that finds no position is itself what leaves an empty sentinel bucket behind, and a later extend can pick it as the target. Link: https://lore.kernel.org/20261024151012.1059683-6-joseph.qi@linux.alibaba.com Fixes: 80bcaf3469b8 ("ocfs2/xattr: Proper hash collision handle in bucket division") Signed-off-by: Joseph Qi Signed-off-by: Andrew Morton Cc: Heming Zhao Cc: Mark Fasheh Cc: Joel Becker Cc: --- fs/ocfs2/xattr.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c index 3a16b4a36d9a..822b1e9c3ba2 100644 --- a/fs/ocfs2/xattr.c +++ b/fs/ocfs2/xattr.c @@ -5228,7 +5228,15 @@ static int ocfs2_divide_xattr_bucket(struct inode *inode, start = ocfs2_xattr_find_divide_pos(xh); if (start == count) { - xe = &xh->xh_entries[start-1]; + /* + * start == count means every entry shares one hash, so the + * first of them carries it too. An empty bucket has no + * entries[start - 1], but its entries[0] still carries the + * bucket key: either the hash ocfs2_xa_remove_entry() + * deliberately leaves behind, or the sentinel a previous + * divide wrote. + */ + xe = &xh->xh_entries[0]; /* * initialized a new empty bucket here.