linux-kernel - [PATCH 5.4 050/104] XArray: Fix infinite loop with entry at ULONG

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Message-Id: <20200128135824.574648455@linuxfoundation.org>
Date:   Tue, 28 Jan 2020 15:00:11 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>
Subject: [PATCH 5.4 050/104] XArray: Fix infinite loop with entry at ULONG_MAX

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

commit 430f24f94c8a174d411a550d7b5529301922e67a upstream.

If there is an entry at ULONG_MAX, xa_for_each() will overflow the
'index + 1' in xa_find_after() and wrap around to 0.  Catch this case
and terminate the loop by returning NULL.

Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Cc: stable@...r.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 lib/test_xarray.c |   17 +++++++++++++++++
 lib/xarray.c      |    3 +++
 2 files changed, 20 insertions(+)

--- a/lib/test_xarray.c
+++ b/lib/test_xarray.c
@@ -1046,11 +1046,28 @@ static noinline void check_find_3(struct
 	xa_destroy(xa);
 }
 
+static noinline void check_find_4(struct xarray *xa)
+{
+	unsigned long index = 0;
+	void *entry;
+
+	xa_store_index(xa, ULONG_MAX, GFP_KERNEL);
+
+	entry = xa_find_after(xa, &index, ULONG_MAX, XA_PRESENT);
+	XA_BUG_ON(xa, entry != xa_mk_index(ULONG_MAX));
+
+	entry = xa_find_after(xa, &index, ULONG_MAX, XA_PRESENT);
+	XA_BUG_ON(xa, entry);
+
+	xa_erase_index(xa, ULONG_MAX);
+}
+
 static noinline void check_find(struct xarray *xa)
 {
 	check_find_1(xa);
 	check_find_2(xa);
 	check_find_3(xa);
+	check_find_4(xa);
 	check_multi_find(xa);
 	check_multi_find_2(xa);
 }
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1847,6 +1847,9 @@ void *xa_find_after(struct xarray *xa, u
 	XA_STATE(xas, xa, *indexp + 1);
 	void *entry;
 
+	if (xas.xa_index == 0)
+		return NULL;
+
 	rcu_read_lock();
 	for (;;) {
 		if ((__force unsigned int)filter < XA_MAX_MARKS)