+ ocfs2-find-the-xattr-entry-again-after-defragmenting-a-bucket.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: ocfs2: find the xattr entry again after defragmenting a bucket
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     ocfs2-find-the-xattr-entry-again-after-defragmenting-a-bucket.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/ocfs2-find-the-xattr-entry-again-after-defragmenting-a-bucket.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Joseph Qi <joseph.qi@linux.alibaba.com>
Subject: ocfs2: find the xattr entry again after defragmenting a bucket
Date: Sat, 24 Oct 2026 23:10:08 +0800

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.

Link: https://lore.kernel.org/20261024151012.1059683-3-joseph.qi@linux.alibaba.com
Fixes: 012255961c9e ("ocfs2: Enable xattr set in index btree")
Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Heming Zhao <heming.zhao@suse.com>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: <stable@vger.kernel.org>
---

 fs/ocfs2/xattr.c |   30 +++++++++++++++++++++++++++++-
 1 file changed, 29 insertions(+), 1 deletion(-)

--- a/fs/ocfs2/xattr.c~ocfs2-find-the-xattr-entry-again-after-defragmenting-a-bucket
+++ a/fs/ocfs2/xattr.c
@@ -6052,13 +6052,18 @@ static int ocfs2_xattr_set_entry_bucket(
 					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(
 		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;
_

Patches currently in -mm which might be from joseph.qi@linux.alibaba.com are

ocfs2-read-the-xattr-entry-hash-before-defragmenting-the-bucket.patch
ocfs2-find-the-xattr-entry-again-after-defragmenting-a-bucket.patch
ocfs2-find-the-xattr-entry-again-after-converting-a-block-to-a-bucket.patch
ocfs2-do-not-read-the-entry-array-of-an-empty-xattr-bucket.patch
ocfs2-do-not-index-before-the-entry-array-when-dividing-an-empty-bucket.patch
ocfs2-do-not-read-the-entry-array-of-an-empty-xattr-block.patch