[RFC PATCH 08/14] khwasan: perform untagged pointers comparison in krealloc

[Andrey Konovalov <andreyknvl@google.com>]

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.
---
 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 a33e61315ca6..7c829cbda1a5 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1494,7 +1494,7 @@ 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((void *)p) != khwasan_reset_tag(ret))
 		kfree(p);
 
 	return ret;
-- 
2.16.2.395.g2e18187dfd-goog

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