[PATCH v12 15/25] kasan, mm: perform untagged pointers comparison in krealloc

[Andrey Konovalov]

The krealloc function checks where the same buffer was reused or a new one
allocated by comparing kernel pointers. Tag-based KASAN 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.

Reviewed-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
 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 5f3504e26d4c..5aabcbd32d82 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1534,7 +1534,7 @@ 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 && kasan_reset_tag(p) != kasan_reset_tag(ret))
 		kfree(p);
 
 	return ret;
-- 
2.20.0.rc0.387.gc7a69e6b6c-goog