linux-kernel - [PATCH] x86-kasan-instrument-user-memory-access-api-fix

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Date:	Tue, 10 May 2016 11:33:29 +0300
From:	Andrey Ryabinin <aryabinin@...tuozzo.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Ingo Molnar <mingo@...nel.org>, <kasan-dev@...glegroups.com>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
	Alexander Potapenko <glider@...gle.com>,
	Dmitry Vyukov <dvyukov@...gle.com>, <x86@...nel.org>,
	Andrey Ryabinin <aryabinin@...tuozzo.com>
Subject: [PATCH] x86-kasan-instrument-user-memory-access-api-fix

Move kasan check under the condition, otherwise we may fail and not
do a user copy.

Reported-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Andrey Ryabinin <aryabinin@...tuozzo.com>
---
 lib/strncpy_from_user.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c
index e3472b0..33f655e 100644
--- a/lib/strncpy_from_user.c
+++ b/lib/strncpy_from_user.c
@@ -104,13 +104,13 @@ long strncpy_from_user(char *dst, const char __user *src, long count)
 	if (unlikely(count <= 0))
 		return 0;
 
-	kasan_check_write(dst, count);
 	max_addr = user_addr_max();
 	src_addr = (unsigned long)src;
 	if (likely(src_addr < max_addr)) {
 		unsigned long max = max_addr - src_addr;
 		long retval;
 
+		kasan_check_write(dst, count);
 		user_access_begin();
 		retval = do_strncpy_from_user(dst, src, count, max);
 		user_access_end();
-- 
2.7.3