[PATCH] sha: prevent removal of memset as dead store in sha1_update()

Roel Kluin
2010-02-25T15:10:36Z

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@gmail.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);