[PATCH 2/6] ocfs2: find the xattr entry again after defragmenting a bucket

[Joseph Qi <joseph.qi@linux.alibaba.com>]

ocfs2_xattr_set_entry_bucket() hands loc.xl_entry to ocfs2_xa_set() twice:
once for the bucket as it stands, and, if that reports -ENOSPC, once more
after ocfs2_defrag_xattr_bucket() has packed the name/value pairs down.

Defragmenting ends by sorting the entry array on xe_name_hash.  Buckets
are kept sorted, so the sort only permutes entries that share a hash, but
lib/sort.c is an unstable heapsort and it does permute them.  loc.xl_entry
is an address inside xh_entries[], so afterwards it denotes whichever
entry landed in that slot rather than the one the search found.

The second ocfs2_xa_set() then works on the wrong entry.  Nothing on that
path compares the entry's name with xi->xi_name, so what happens depends
on how the two entries compare in size: ocfs2_xa_reuse_entry() trips its
BUG_ON() when the padded name sizes differ, and otherwise the new value is
written into the neighbouring attribute's value slot while the attribute
being set is left untouched.  setxattr() reports success either way.

Remember the entry's hash before defragmenting and look the entry up
again afterwards, the way ocfs2_xattr_bucket_find() does.  An entry that
cannot be found again means the bucket no longer holds what the search
found, so fail with -EFSCORRUPTED rather than writing through the stale
pointer.

Fixes: 012255961c9e ("ocfs2: Enable xattr set in index btree")
Cc: <stable@vger.kernel.org>
Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
---
 fs/ocfs2/xattr.c | 30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

diff --git a/fs/ocfs2/xattr.c b/fs/ocfs2/xattr.c
index bb5b12924e1b..d6d07116ce97 100644
--- a/fs/ocfs2/xattr.c
+++ b/fs/ocfs2/xattr.c
@@ -6052,13 +6052,18 @@ static int ocfs2_xattr_set_entry_bucket(struct inode *inode,
 					struct ocfs2_xattr_search *xs,
 					struct ocfs2_xattr_set_ctxt *ctxt)
 {
-	int ret;
+	int ret, found = 0;
+	u16 xe_index;
+	u32 name_hash;
 	struct ocfs2_xa_loc loc;
 
 	trace_ocfs2_xattr_set_entry_bucket(xi->xi_name);
 
 	ocfs2_init_xattr_bucket_xa_loc(&loc, xs->bucket,
 				       xs->not_found ? NULL : xs->here);
+	/* Defragmenting below may move this entry, so remember its hash. */
+	name_hash = loc.xl_entry ? le32_to_cpu(loc.xl_entry->xe_name_hash) : 0;
+
 	ret = ocfs2_xa_set(&loc, xi, ctxt);
 	if (!ret) {
 		xs->here = loc.xl_entry;
@@ -6077,6 +6082,29 @@ static int ocfs2_xattr_set_entry_bucket(struct inode *inode,
 		goto out;
 	}
 
+	/*
+	 * ocfs2_defrag_xattr_bucket() sorts the entries by name hash and
+	 * lib/sort.c is not stable, so entries sharing a hash may have traded
+	 * slots.  Look the entry up again before writing through it.
+	 */
+	if (loc.xl_entry) {
+		ret = ocfs2_find_xe_in_bucket(inode, xs->bucket,
+					      xi->xi_name_index, xi->xi_name,
+					      name_hash, &xe_index, &found);
+		if (ret) {
+			mlog_errno(ret);
+			goto out;
+		}
+		if (!found) {
+			mlog(ML_ERROR, "xattr entry not found in bucket %llu after defrag\n",
+			     (unsigned long long)bucket_blkno(xs->bucket));
+			ret = -EFSCORRUPTED;
+			goto out;
+		}
+		loc.xl_entry = &bucket_xh(xs->bucket)->xh_entries[xe_index];
+		xs->here = loc.xl_entry;
+	}
+
 	ret = ocfs2_xa_set(&loc, xi, ctxt);
 	if (!ret) {
 		xs->here = loc.xl_entry;
-- 
2.39.3