linux-kernel - [PATCH 5.17 282/298] mm/huge_memory: Fix xarray node memory leak

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Date:   Mon, 13 Jun 2022 12:12:56 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+9e27a75a8c24f3fe75c1@...kaller.appspotmail.com,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>
Subject: [PATCH 5.17 282/298] mm/huge_memory: Fix xarray node memory leak

From: Matthew Wilcox (Oracle) <willy@...radead.org>

commit 69a37a8ba1b408a1c7616494aa7018e4b3844cbe upstream.

If xas_split_alloc() fails to allocate the necessary nodes to complete the
xarray entry split, it sets the xa_state to -ENOMEM, which xas_nomem()
then interprets as "Please allocate more memory", not as "Please free
any unnecessary memory" (which was the intended outcome).  It's confusing
to use xas_nomem() to free memory in this context, so call xas_destroy()
instead.

Reported-by: syzbot+9e27a75a8c24f3fe75c1@...kaller.appspotmail.com
Fixes: 6b24ca4a1a8d ("mm: Use multi-index entries in the page cache")
Cc: stable@...r.kernel.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 include/linux/xarray.h |    1 +
 lib/xarray.c           |    5 +++--
 mm/huge_memory.c       |    3 +--
 3 files changed, 5 insertions(+), 4 deletions(-)

--- a/include/linux/xarray.h
+++ b/include/linux/xarray.h
@@ -1506,6 +1506,7 @@ void *xas_find_marked(struct xa_state *,
 void xas_init_marks(const struct xa_state *);
 
 bool xas_nomem(struct xa_state *, gfp_t);
+void xas_destroy(struct xa_state *);
 void xas_pause(struct xa_state *);
 
 void xas_create_range(struct xa_state *);
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -264,9 +264,10 @@ static void xa_node_free(struct xa_node
  * xas_destroy() - Free any resources allocated during the XArray operation.
  * @xas: XArray operation state.
  *
- * This function is now internal-only.
+ * Most users will not need to call this function; it is called for you
+ * by xas_nomem().
  */
-static void xas_destroy(struct xa_state *xas)
+void xas_destroy(struct xa_state *xas)
 {
 	struct xa_node *next, *node = xas->xa_alloc;
 
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2736,8 +2736,7 @@ out_unlock:
 	if (mapping)
 		i_mmap_unlock_read(mapping);
 out:
-	/* Free any memory we didn't use */
-	xas_nomem(&xas, 0);
+	xas_destroy(&xas);
 	count_vm_event(!ret ? THP_SPLIT_PAGE : THP_SPLIT_PAGE_FAILED);
 	return ret;
 }