linux-kernel - [PATCH] z3fold: fix the potential encode bug in encod

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Date:   Thu, 13 Oct 2016 11:33:05 +0800
From:   zhongjiang <zhongjiang@...wei.com>
To:     <vitalywool@...il.com>, <david@...morbit.com>,
        <sjenning@...hat.com>, <ddstreet@...e.org>,
        <akpm@...ux-foundation.org>, <mhocko@...nel.org>, <vbabka@...e.cz>
CC:     <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>
Subject: [PATCH] z3fold: fix the potential encode bug in encod_handle

From: zhong jiang <zhongjiang@...wei.com>

At present, zhdr->first_num plus bud can exceed the BUDDY_MASK
in encode_handle, it will lead to the the caller handle_to_buddy
return the error value.

The patch fix the issue by changing the BUDDY_MASK to PAGE_MASK,
it will be consistent with handle_to_z3fold_header. At the same time,
The code will much comprehensible to change the BUDDY_MASK to
BUDDIES_MAX in handle_to_buddy.

Signed-off-by: zhong jiang <zhongjiang@...wei.com>
---
 mm/z3fold.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/z3fold.c b/mm/z3fold.c
index 8f9e89c..5884b9e 100644
--- a/mm/z3fold.c
+++ b/mm/z3fold.c
@@ -169,7 +169,7 @@ static unsigned long encode_handle(struct z3fold_header *zhdr, enum buddy bud)
 
 	handle = (unsigned long)zhdr;
 	if (bud != HEADLESS)
-		handle += (bud + zhdr->first_num) & BUDDY_MASK;
+		handle += (bud + zhdr->first_num) & PAGE_MASK;
 	return handle;
 }
 
@@ -183,7 +183,7 @@ static struct z3fold_header *handle_to_z3fold_header(unsigned long handle)
 static enum buddy handle_to_buddy(unsigned long handle)
 {
 	struct z3fold_header *zhdr = handle_to_z3fold_header(handle);
-	return (handle - zhdr->first_num) & BUDDY_MASK;
+	return (handle - zhdr->first_num) & BUDDIES_MAX;
 }
 
 /*
-- 
1.8.3.1