kasan: fix last shadow judgement in memory_is_poisoned_16()

The shadow which correspond 16 bytes memory may span 2 or 3 bytes.  If
the memory is aligned on 8, then the shadow takes only 2 bytes.  So we
check "shadow_first_bytes" is enough, and need not to call
"memory_is_poisoned_1(addr + 15);".  But the code "if
(likely(!last_byte))" is wrong judgement.

e.g.  addr=0, so last_byte = 15 & KASAN_SHADOW_MASK = 7, then the code
will continue to call "memory_is_poisoned_1(addr + 15);"

Signed-off-by: Xishi Qiu <[email protected]>
Acked-by: Andrey Ryabinin <[email protected]>
Cc: Andrey Konovalov <[email protected]>
Cc: Rusty Russell <[email protected]>
Cc: Michal Marek <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/kasan/kasan.c b/mm/kasan/kasan.c
index 7b28e9cdf1c7686428fe49802fced44088043555..8da211411b57f1b0db116d8d67401bae30628ec8 100644 (file)
--- a/mm/kasan/kasan.c
+++ b/mm/kasan/kasan.c
@@ -135,12 +135,11 @@ static __always_inline bool memory_is_poisoned_16(unsigned long addr)
 
        if (unlikely(*shadow_addr)) {
                u16 shadow_first_bytes = *(u16 *)shadow_addr;
-               s8 last_byte = (addr + 15) & KASAN_SHADOW_MASK;
 
                if (unlikely(shadow_first_bytes))
                        return true;
 
-               if (likely(!last_byte))
+               if (likely(IS_ALIGNED(addr, 8)))
                        return false;
 
                return memory_is_poisoned_1(addr + 15);