linux-kernel - [PATCH] damon: vaddr-test: fix a missing check on list iterator

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Message-Id: <20220327080345.12295-1-xiam0nd.tong@gmail.com>
Date:   Sun, 27 Mar 2022 16:03:45 +0800
From:   Xiaomeng Tong <xiam0nd.tong@...il.com>
To:     sj@...nel.org, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Xiaomeng Tong <xiam0nd.tong@...il.com>, stable@...r.kernel.org
Subject: [PATCH] damon: vaddr-test: fix a missing check on list iterator

The bug is here:
	KUNIT_EXPECT_EQ(test, r->ar.start, start + i * expected_width);
	KUNIT_EXPECT_EQ(test, r->ar.end, end);

For the damon_for_each_region(), just like list_for_each_entry(),
the list iterator 'drm_crtc' will point to a bogus position
containing HEAD if the list is empty or no element is found.
This case must be checked before any use of the iterator,
otherwise it will lead to a invalid memory access.

To fix this bug, just mov two KUNIT_EXPECT_EQ() into the loop
when found.

Cc: stable@...r.kernel.org
Fixes: 044cd9750fe01 ("mm/damon/vaddr-test: split a test function having >1024 bytes frame size")
Signed-off-by: Xiaomeng Tong <xiam0nd.tong@...il.com>
---
 mm/damon/vaddr-test.h | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/mm/damon/vaddr-test.h b/mm/damon/vaddr-test.h
index 6a1b9272ea12..98b7a9f54b35 100644
--- a/mm/damon/vaddr-test.h
+++ b/mm/damon/vaddr-test.h
@@ -281,14 +281,16 @@ static void damon_test_split_evenly_succ(struct kunit *test,
 	KUNIT_EXPECT_EQ(test, damon_nr_regions(t), nr_pieces);
 
 	damon_for_each_region(r, t) {
-		if (i == nr_pieces - 1)
+		if (i == nr_pieces - 1) {
+			KUNIT_EXPECT_EQ(test,
+				r->ar.start, start + i * expected_width);
+			KUNIT_EXPECT_EQ(test, r->ar.end, end);
 			break;
+		}
 		KUNIT_EXPECT_EQ(test,
 				r->ar.start, start + i++ * expected_width);
 		KUNIT_EXPECT_EQ(test, r->ar.end, start + i * expected_width);
 	}
-	KUNIT_EXPECT_EQ(test, r->ar.start, start + i * expected_width);
-	KUNIT_EXPECT_EQ(test, r->ar.end, end);
 	damon_free_target(t);
 }
 
-- 
2.17.1