[PATCH AUTOSEL 5.10 53/53] kasan: test: avoid corrupting memory in kasan_rcu_uaf

From: Andrey Konovalov <andreyknvl@gmail.com>

[ 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@gmail.com
Signed-off-by: Andrey Konovalov <andreyknvl@gmail.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <redacted>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 2d68db6ae67b..1c6e06136f78 100644
--- a/lib/test_kasan_module.c
+++ b/lib/test_kasan_module.c

@@ -73,7 +73,7 @@ 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