linux-kernel - [PATCH v9 04/19] crypto: scomp - Fix off-by-one bug when calculating last page

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Message-Id: <20250508194134.28392-5-kanchana.p.sridhar@intel.com>
Date: Thu,  8 May 2025 12:41:19 -0700
From: Kanchana P Sridhar <kanchana.p.sridhar@...el.com>
To: linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	hannes@...xchg.org,
	yosry.ahmed@...ux.dev,
	nphamcs@...il.com,
	chengming.zhou@...ux.dev,
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	ryan.roberts@....com,
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	ying.huang@...ux.alibaba.com,
	akpm@...ux-foundation.org,
	senozhatsky@...omium.org,
	linux-crypto@...r.kernel.org,
	herbert@...dor.apana.org.au,
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Cc: wajdi.k.feghali@...el.com,
	vinodh.gopal@...el.com,
	kanchana.p.sridhar@...el.com
Subject: [PATCH v9 04/19] crypto: scomp - Fix off-by-one bug when calculating last page

Fix off-by-one bug in the last page calculation for src and dst.

Reported-by: Nhat Pham <nphamcs@...il.com>
Fixes: 2d3553ecb4e3 ("crypto: scomp - Remove support for some non-trivial SG lists")
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
---
 crypto/scompress.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/crypto/scompress.c b/crypto/scompress.c
index c1ce12564299..1ed52b9740c5 100644
--- a/crypto/scompress.c
+++ b/crypto/scompress.c
@@ -215,8 +215,8 @@ static int scomp_acomp_comp_decomp(struct acomp_req *req, int dir)
 			spage = nth_page(spage, soff / PAGE_SIZE);
 			soff = offset_in_page(soff);
 
-			n = slen / PAGE_SIZE;
-			n += (offset_in_page(slen) + soff - 1) / PAGE_SIZE;
+			n = (slen - 1) / PAGE_SIZE;
+			n += (offset_in_page(slen - 1) + soff) / PAGE_SIZE;
 			if (PageHighMem(nth_page(spage, n)) &&
 			    size_add(soff, slen) > PAGE_SIZE)
 				break;
@@ -243,9 +243,9 @@ static int scomp_acomp_comp_decomp(struct acomp_req *req, int dir)
 			dpage = nth_page(dpage, doff / PAGE_SIZE);
 			doff = offset_in_page(doff);
 
-			n = dlen / PAGE_SIZE;
-			n += (offset_in_page(dlen) + doff - 1) / PAGE_SIZE;
-			if (PageHighMem(dpage + n) &&
+			n = (dlen - 1) / PAGE_SIZE;
+			n += (offset_in_page(dlen - 1) + doff) / PAGE_SIZE;
+			if (PageHighMem(nth_page(dpage, n)) &&
 			    size_add(doff, dlen) > PAGE_SIZE)
 				break;
 			dst = kmap_local_page(dpage) + doff;
-- 
2.27.0