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From:   Andrey Konovalov <andreyknvl@google.com>
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        Andrey Konovalov <andreyknvl@google.com>
Subject: [PATCH v4 10/17] khwasan, mm: perform untagged pointers comparison in krealloc
Date:   Tue, 26 Jun 2018 15:15:20 +0200
Message-Id: <be2d28030622fa8201844cf438654568ae1808e0.1530018818.git.andreyknvl@google.com>
In-Reply-To: <cover.1530018818.git.andreyknvl@google.com>
References: <cover.1530018818.git.andreyknvl@google.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

The krealloc function checks where the same buffer was reused or a new one
allocated by comparing kernel pointers. KHWASAN changes memory tag on the
krealloc'ed chunk of memory and therefore also changes the pointer tag of
the returned pointer. Therefore we need to perform comparison on untagged
(with tags reset) pointers to check whether it's the same memory region or
not.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 mm/slab_common.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index c279b52c7565..7746d2ef5d45 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1509,7 +1509,7 @@ void *krealloc(const void *p, size_t new_size, gfp_t flags)
 	}
 
 	ret = __do_krealloc(p, new_size, flags);
-	if (ret && p != ret)
+	if (ret && khwasan_reset_tag(p) != khwasan_reset_tag(ret))
 		kfree(p);
 
 	return ret;
-- 
2.18.0.rc2.346.g013aa6912e-goog