linux-kernel - [PATCH] sha: prevent removal of memset as dead store in sha1

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Message-ID: <4B8692E3.9030509@gmail.com>
Date:	Thu, 25 Feb 2010 16:10:27 +0100
From:	Roel Kluin <roel.kluin@...il.com>
To:	Herbert Xu <herbert@...dor.apana.org.au>,
	Mikael Pettersson <mikpe@...uu.se>,
	"David S. Miller" <davem@...emloft.net>,
	linux-crypto@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] sha: prevent removal of memset as dead store in sha1_update()

Due to optimization A call to memset() may be removed as a dead store when
the buffer is not used after its value is overwritten.

Signed-off-by: Roel Kluin <roel.kluin@...il.com>
---
see http://cwe.mitre.org/data/slices/2000.html#14

checkpatch.pl, compile and sparse tested. Comments?

diff --git a/crypto/sha1_generic.c b/crypto/sha1_generic.c
index 0416091..86de0da 100644
--- a/crypto/sha1_generic.c
+++ b/crypto/sha1_generic.c
@@ -49,8 +49,8 @@ static int sha1_update(struct shash_desc *desc, const u8 *data,
 	src = data;
 
 	if ((partial + len) > 63) {
-		u32 temp[SHA_WORKSPACE_WORDS];
-
+		u32 *temp = kzalloc(SHA_WORKSPACE_WORDS * sizeof(u32),
+				GFP_KERNEL);
 		if (partial) {
 			done = -partial;
 			memcpy(sctx->buffer + partial, data, done + 64);
@@ -64,6 +64,7 @@ static int sha1_update(struct shash_desc *desc, const u8 *data,
 		} while (done + 63 < len);
 
 		memset(temp, 0, sizeof(temp));
+		kfree(temp);
 		partial = 0;
 	}
 	memcpy(sctx->buffer + partial, src, len - done);
--
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