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

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Message-ID: <aAW8E9NrKWq1Xk2w@gondor.apana.org.au>
Date: Mon, 21 Apr 2025 11:31:31 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Nhat Pham <nphamcs@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	"Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>,
	Yosry Ahmed <yosry.ahmed@...ux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	"chengming.zhou@...ux.dev" <chengming.zhou@...ux.dev>,
	"usamaarif642@...il.com" <usamaarif642@...il.com>,
	"ryan.roberts@....com" <ryan.roberts@....com>,
	"21cnbao@...il.com" <21cnbao@...il.com>,
	"ying.huang@...ux.alibaba.com" <ying.huang@...ux.alibaba.com>,
	"linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
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	"surenb@...gle.com" <surenb@...gle.com>,
	"Accardi, Kristen C" <kristen.c.accardi@...el.com>,
	"Feghali, Wajdi K" <wajdi.k.feghali@...el.com>,
	"Gopal, Vinodh" <vinodh.gopal@...el.com>, m95d@...hoexpert.ro
Subject: [PATCH] crypto: scomp - Fix off-by-one bug when calculating last page

On Sun, Apr 20, 2025 at 04:35:44PM -0700, Nhat Pham wrote:
>
> Anyhow, this looks like a crypto/compression infra bug. Herbert, does
> this ring any bell for you?

Yes this looks like an off-by-one bug in the new scomp scratch
code.

---8<---
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>

diff --git a/crypto/scompress.c b/crypto/scompress.c
index 5762fcc63b51..36934c78d127 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;
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt