[PATCH AUTOSEL 5.14 99/99] kasan: test: avoid corrupting memory in kasan_rcu_uaf

[Sasha Levin]

From: Andrey Konovalov <andreyknvl@xxxxxxxxx>

[ Upstream commit f16de0bcdb55bf18e2533ca625f3e4b4952f254c ]

kasan_rcu_uaf() writes to freed memory via kasan_rcu_reclaim(), which is
only safe with the GENERIC mode (as it uses quarantine).  For other modes,
this test corrupts kernel memory, which might result in a crash.

Turn the write into a read.

Link: https://lkml.kernel.org/r/b6f2c3bf712d2457c783fa59498225b66a634f62.1628779805.git.andreyknvl@xxxxxxxxx
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
Reviewed-by: Marco Elver <elver@xxxxxxxxxx>
Cc: Alexander Potapenko <glider@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 lib/test_kasan_module.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/test_kasan_module.c b/lib/test_kasan_module.c
index fa73b9df0be4..7ebf433edef3 100644
--- a/lib/test_kasan_module.c
+++ b/lib/test_kasan_module.c
@@ -71,7 +71,7 @@ static noinline void __init kasan_rcu_reclaim(struct rcu_head *rp)
 						struct kasan_rcu_info, rcu);
 
 	kfree(fp);
-	fp->i = 1;
+	((volatile struct kasan_rcu_info *)fp)->i;
 }
 
 static noinline void __init kasan_rcu_uaf(void)
-- 
2.30.2